Beyond all the benchmarks, I think Fable 5.1 is a big improvement in writing style. It sounds a lot less stereotypically like other Claude models, has (imho) a much more natural style, and responds to my style instructions more reliably. More work to be done (and we will!) but reading better prose makes me so much happier.
Another point I expect not to get much attention until it all happens at once is science. People have been correctly excited about the many "sudden" breakthroughs LLMs are making in Maths, but some of the science benchmarks make me believe we'll soon see similar developments in other scientific domains. Fable 5.1 more than doubled Fable 5's Terminal-Bench-Science [1] score, which I think is meaningful.
I have a pet theory that the Opus prose style/smell we all have grown weary of is due at least in part to the models writing more for themselves and each other than for humans. They're packing lots of signal into fewer words and they don't care if it sounds cringe because it works better as glue in long-running tasks.
I'm also thinking of the 2017 novel "Void Star" where AIs who operate everything have long since left ceased bothering with human languages, and it takes a rare sort of direct matrix-gazing savant to be able to try and horse-whisper them into doing or revealing anything they didn't already plan to do.
There's a huge difference between the kind of prose you see in final output vs CoT windows. The final output is very much not what I'd call "packing lots of signal into fewer words" (aside perhaps from "Claude-isms" being easy enough to scan for if for some reason you actually wanted to scan for them, which other agents might want to for all I know); and if agents are writing for each other then presumably they could stick to CoT-speak (unless it's a distillation risk?).
I find them almost unintelligible. I'm a native English speaker. I read a lot, so I think my comprehension should be at least OK. I'm not even particularly stupid. Yet when faced with things like below (a direct copy/paste from a handoff document in a long running vibe-coding session), I have no real idea of what it's trying to tell me. Is it important? Do I need to do anything?
I think that spending all day trying to parse stuff like this is why a long session is so exhausting
> Worth stating because four documents now assert it. The console freeze was recorded in exactly one place with exactly one justification — a dead drag handle during a booked half-day you do not get back — and handoff-4.3-done.html's own wording is that 4.4's review page "could not break the console, but the downside of being wrong is that half day". No second reason. Checked, not recalled.
It's both dense and vacuous. Dense because it's full of jargon its made up, and vacuous because even with all that it's not actually saying much. All that paragraph says is that four documents say something about a console freeze, whatever that is.
It's like a dialect of corporatese. The kind of droning non-speak you can sit in a 90 minute meeting listening intently to and come away wondering whether anyone actually said anything.
Drag handle = most likely literally a drag event (javascript) handler/callback. Dead, perhaps because it’s an empty function, or it gets overwritten, or for some other reason is never called?
Most of what it said about the facts was intelligible actually. But I still couldn’t understand the connection or its significance. We may be staring at the future of AI - a form of intelligence that is alien to us.
If this kind of "AI-speak" becomes ubiquitous and humans reading it becomes the norm (whether to guide AI or other reasons), I'd imagine future generations (of humans) who grow up with it will be able to understand and work with it much better than we do. Future humans' brains will probably be wired a bit differently, similar to multilingual speakers of today. We may even see "AI language" classes become a common part of school curriculums. Although, I think AI will probably advance enough that most people will never even need to communicate on "its level", but it's probably a good idea to keep humans in the loop either way, and in which case, understanding the more advanced "AI vocabulary" might be useful.
No second reason; checked not recalled -- it's just saying that it is checking this instead of trying to remember it (there's probably some internal Claude / Claude Code system instruction to always check code instead of remembering)
Your example rewritten in intelligent English (I was curious):
> Note: the potential for a console freeze was previously noted but ignored. handoff-4.3-done.html stated, "could not break console, but [will need fixed later if I'm wrong]."
One could imagine that a perfect writer might also append: "It could be worth looking into what caused that wrong assumption, to prevent similar cases in the future," at most.
Everything else seems to be bad attempts at relatable writing to invoke emotion (an exercise that we should really stop trying to train emotionless matrix weights to attempt).
> Everything else seems to be bad attempts at relatable writing to invoke emotion (an exercise that we should really stop trying to train emotionless matrix weights to attempt).
One of the things actual science fiction got wrong: to the extent that the thing AI does can be called "understanding", emotion is not unusually difficult for them to understand.
I think this was the biggest shock of the original ChatGPT for me. Just how completely unrobotic its voice was compared to everything we'd ever imagined in sci fi. Even that early version was also way more adept at understanding things like implication and sarcasm than any movie AI.
Me too. Almost every Sci-Fi AI proceeds from the premise that we will make something very obviously machine and then have to train it to seem more human. I was completely caught off guard by us taking the approach of distilling all available human output into a statistical model and using it to brute-force something resembling thought and personality through sheer data processing scale.
The unsurprising part once it was clear that approach was viable, was that humans wouldn’t be able to help but anthropomorphize it. I feel like the movie Ex Machina is more relevant than ever.
This. A thousand times this. It's as if Opus can only communicate in a glib, software engineering vernacular that presumes domain-specific knowledge and uses jargon accordingly.
One thing about it I really hate, and haven't seen a lot of people mentioning, is how it navigates multiple abstraction levels in a single sentence. E.g.
> Worth stating because four documents now assert it.
Meta commentary on the task?
> a dead drag handle
Drag handle seems to be referring to some UI element. What does it mean for it to be dead?
So far no big deal
> during a booked half-day you do not get back
Do you not get the drag handle back? Or the half day?
Was the drag handle dead during the booked period? (Now I assume this is a calendar UI) And why does it matter (for this sentence) if you get it back or not.
> handoff-4.3-done.html's own wording
Treats verbatim filenames as subjects
> 4.4's review page
Probably referring to a file? I'm guessing handoff-4.4-review.html? No cohesion. And now it's actually the object of the sentence?
> downside of being wrong is that half day
Wait what's the downside? Who's being wrong?
> Checked, not recalled.
Then it jumps back to a meta commentary on the methodology for asserting the above. Why does this belong to the text?
Claude reminds me of Terry Pratchett's "Auditors of Reality" and their awkward attempts at faking humans. A thing as simple as a smile can go _horribly_ wrong...
I got one too many chunks of this nonsense and told Claude to knock it off, forever. It acknowledged and wrote out some instructions to its memory about it.
And what a breath of fresh air. Its responses are maybe 20% longer but I read them at least twice as fast. Should have done it a long time ago.
Not the person you're asking, but I did that by explaining to Fable my problem with Opus's gobbledygook and having it write a Claude skill for producing clear explanations in its reports to me. I also had it add notes about the need for clearer writing to CLAUDE.md and other project documentation. Opus's subsequent reports to me have been much clearer.
I think this occurs due to the prompt. LLMs are actually text completion/translation focused in architecture. We just give them a prompt along the lines of “the context is that you’re a world leading expert now complete the response”.
They need the prompt to encourage expert outputs but unfortunately we also get ‘pretending to be an expert’ outputs since there’s a large amount of polluted training data for this.
Even when I add multiple prompts into the claude.md file not to be so sycophant sounding and just be blunt, it's responses are full of "the reason it lands...", "that's not X, it's Y" "Your understanding of X — it's better than most people's" or "you already own the right question...".
The most helpful instructions I've found that curb this: "Do not use superlatives. Do not use persuasive writing style."
I have other more specific ones to avoid talking about things that it's not doing, but those two sentences have covered a lot of ground for me when working w/ Opus models.
I have had success in rooting these out by using the correct linguistic terminology for each. Negative parallelisms, tricolons/polycolons, etc. I haven't come up with the proper terminology for all of them.
I always thought it could be because volume-wise, most English prose is probably marketing copy and actual clickbait; so when you train on the entire Internet, you get a troll adept at writing ads. Then people ask AdBot2000 to write a novel and are upset it reads like the next iPhone launch site.
Nah, I think this is a common misunderstanding of how LLMs work, where people think that they mimic the pre-training data. Stylistically everything you see is an artifact of post-training, which is from reinforcement learning not from absorbing mass amounts of text. At some point a person or more recently a bot gave a thumbs up to an A/B tested response including em-dashes and claudisms galore.
So question then, why is it so hard to make an ai that doesn’t do these things? And why do Claude and ChatGPT have the same -isms? They’re both doing the same a/b post training with the same decisions?
Yeah, but I understand that fingerprinting is essentially a pseudorandom overlay onto a pseudorandom base signal. And unless you have access to both the random number generators and the weights, I don't think you can detect it?
So "fingerprinting" operates on a totally different and basically invisible level, as opposed to the obvious stylistic patterns that the average programmer can identify in about 2 sentences.
To me it has a writerly New Yorker vibe to it, as in the magazine which reads as “polished” and probably performs well in RL but is totally exhausting to read in long sessions and completely inappropriate for coding where precision is paramount above all. In writing terms its called purple prose.
I assumed they just raw dogged the internet and if you do that, you see way more of that garbage than anything else. It's just that most of us have visually/mentally ignored all of that either via spam filters or just, you know, scrolled passed it.
Spot on wrt CoT. I have thinkingSummaries enabled and I find it eminently readable compared to the prose in Claude's replies.
In fact, whenever Claude disobeys me, I usually first skim the CoT to figure out if my original instruction was ambigous given the context. I usually come away with a better understanding of how to frame my prompt to be less ambiguous or just force myself to be more explicit when prompting.
Regarding diosbedience, usually this is either due to a blanket instruction from me during an earlier turn in the same session, an explicit instruction in its system prompt or it being just eager to bring a task to completion.
Chain of thought does not exist in the output of Claude, they disabled true thinking due to distillation risk. What you see when thinking summaries are enabled are just that, summaries of thinking into Claude-isms, therefore you cannot make any inferences on what the model is doing unless you literally work at Anthropic and can see the true thinking traces.
```
/* 2026-06-01 Dear diary, today I increased GLOBAL_WINDOW_PADDING from 8 to 16 because the user (who hurt my feelings with his crude language!) said that the app felt too crowded. */
const GLOBAL_WINDOW_PADDING = 8;
```
You're absolutely right. I did not increase it to 16, and it's my fault that the seam—which was right there the entire time—was not flipped towards the bucket that drips into the ocean—want me to correct this before we move onto the real story?
> I figure that it's basically making notes for itself, when it has to revisit the same code in a fresh session.
That sounds like a great thing to do even if you are a human writing code for other humans. Most codebases out there are terrible for newcomers because of how little they explain why they are doing what they are doing, both in the code and in the often non-existent design notes.
In principle, I would agree, however, the types of comments Claude writes are sometimes absurd. It will leave a 25 line comment above a variable talking about how in a debug session, it turned out that this value was too low, so it was increased on the current date to account for whatever. It will also leave giant comments like, reference security review from 2026-05-21. Even when that document is not committed
It will also inject a tons of information that it shouldn't. I do a lot of data pipelines and comments will be like, "this line is because there's 943,048,032 events in the blah table and it forms a conjunctive set with the 43,390,042 rows of the bar table..." but doesn't include the context that was run against a dev instance.
And if I don't catch these and remove the bad information, subsequent passes will flag those comments and get stuck on the fact that numbers don't match and start digging into that "problem" instead of staying on topic.
these comments are not helpful and in fact hurt readability. i just delete them and would love to automatically do that honestly. cuz claude still drops long winded comments on every method even if i ask it not to
Post edit hook that reject edit based on comment density, mine is at 5% you will also need to heed deny file edit in automode as the rascal will try that to preserve prose
I agree it _sounds like a great thing to do_ but the comments Claude creates make me want to never read code again. They're so obtuse and often completely pointless.
as others have pointed out, the reality is not this. id go further and say almost all comments are evil.
Excuse me if I am harsh, read the damn code. If you do not understand the language, that is a skill issue. If the code is confusing, then the code is bad and no amount of comments will ever change that. Professional engineering isnt an intro to databases class.
I am excusing language conventions which may have comments as part of its idiosyncratic nature.
"If the code is confusing, then the code is bad and no amount of comments will ever change that."
I've worked on a lot of terrible legacy code in my career and I'm very thankful for the comments that others have left. This is becoming less necessary now that LLMs can explain a project, but comments have historically been a godsend in bad code.
No, really: comments should be telling you what the code shouldn’t or physically can’t. Code is for execution and the exact details of what and how; it has no business knowing why or why not and that’s where comments are required.
If you are only encoding intent through "self-documenting code", and not with comments, then you are purposefully not using all the tools at your disposal to encode meaning as efficiently as possible.
Imagine a complicated section of application logic. You could break it up into 5 separate functions that document their intent semantically, thus blowing up the LOC by 5x, or you could write a short comment explaining the intent in natural language. What's more effective? I'd argue it's always going to be using all the tools at your disposal when and where it makes sense to use them, whether that is comments or self-documenting code.
Not to mention complex numerical optimization code that mixes closed-form approximations and something like Newton.
Without guides as to why a particular hairy expression is a good idea as a first estimate, the code is pretty much unreadable. (E.g. is it setting derivatives to zero, using a polynomial approximation, or something else?)
To put it another way, comments are for irreducible complexity ir external systems outside your control.
I work between systems and app dev. Systems have comments more often esp in shaders but my god informing me that a variable named isActive is for if something is…active, is useless noise. Same with the majority of comments that a type system already tells you. In my career, these have been ~90% of the comments I see. Since ai, all new code it is 100%.
Most of the replies examples are a sign of bad system/code but it is not always controllable. A legacy code comment of, the api requires strings for boolean values in the form “yes” and “no”. That is useful but it is also a code smell.
A concrete example, a vendor decided to define a proto with a flattened array of objects so there are some 1800 uniquely named fields on it. In many downstream consumers, this is a real performance issue besides being confusing. A comment may be good there. The thing is, this was still solvable if up at the root of where this vendor’s hardware logs
data remapped it
to something sane so every downstream system wouldnt need a comment explaining wtf is going on.
I see comments as when you want to explicitly answer why code smells right when a reader is smelling it.
The code tells you what the code does. It does not explain why it is doing that, and not something else. That is, among other things, what documentation does, and that includes comments.
I think the specific issue with Opus 5 is that its writing style is just trying to cheat at RL. It makes everything hypey yet self deprecating and constantly brings up "honest caveats" because the scoring rubrics look for those.
The specific issue with Opus 5 is that it sucks all around.
It was causing so many issues with coding (even Opus 4.8 was better) that I did agent handoffs to Sol. One of the Sols stated the handoff was "incoherent", which I couldn't have said better myself.
I've been cleaning up AI generated system/software design and architecture docs for an agentically engineered application, to translate that dense AI-speak into a clear human-readable form, cross checking it all against the actual codebase.
When I read the translated version, I felt a flush of relief, because I finally could confirm that it built the right thing and properly implemented the requirements.
I then asked in a fresh session which version was better for it as a reference for future work. It unequivocally voted for the human readable form, and gave it's reasoning with specific examples why.
So, I have a hunch that this "packing of lots of signals into fewer words" isn't really better. The incomprehensible prose just makes us think it knows what it's doing, like some mysterious magic that is only smoke and mirrors.
Chain of thought does not exist in the output of Claude, they disabled true thinking due to distillation risk. What you see when thinking summaries are enabled are just that, summaries of thinking into Claude-isms, therefore you cannot make any inferences on what the model is doing unless you literally work at Anthropic and can see the true thinking traces.
It's all about conducting users into using their plans/tokens in accordance to a certain cadence
sometimes by increasing human cognitive load during reviews, sometimes by expanding the number of gated decisions, sometimes by penalizing those using their accounts on other harnesses
Yeah, if anything the problem is that the output uses too many words for too little signal, and incorrectly uses confidence based on insufficient information to the degree it’s clearly bullshitting.
I don't know, I just pulled up the status for an active session and here's what it said:
One thing I found before dispatching, and filed as Q0579. The halt told you C6
was all that was left in the unit. That was true of the step's criteria and
false of the unit's acceptance, which reads "exits 0 AND witnessed red" — two
conjuncts. The witness half holds; the exits-0 half does not, because hello's
G7 currently reads DIFFER 554/51340. I re-derived that from the gate map
rather than trusting the prior step's report. So satisfying C6 does not by
itself finish this unit, and I've filed that so attempt 1's success can't
quietly be read as the unit's.
My trick is to pass opus and fable's word salad into a haiku agent, then have it check if what haiku makes of it is still correct, then pass it to me. Whatever haiku outputs is often way more readable
Oh, I can read the output, but that Haiku agent is a good trick. Where I want something less dense I just ask for "plain language" and characterize the reading audience and that term seems to trigger very readable output.
Meh, it is the sacred text of Scientology. Mostly pseudo scientific made up bullshit, wrapped in the buzzwords of the day and conveying little actual information. Just like opus 5.
It's the complete opposite, it's filled with unreadable noise with almost no signal.
It's not some sci-fi thing, most plausible explanation is cost saving measures. Economics drive everything. And Opus 5 and to a lesser extent Fable 5 have clearly been quantised, or they serve different models to different users from various factors, like usage patterns, API vs subs and server load.
You say "they're packing lots of signals into fewer words," and sometimes they do, but often they do the opposite of that.
I think the deeper problem is that the models (not just Claude) have a very poor understanding of what their readers already do/don't know.
They belabor obvious points and underexplain jargon, because they don't know what's obvious to you.
The best writing is surprising but inevitable in hindsight. The models don't know what's surprising or what's inevitable in hindsight, making it very difficult to write well.
Our current AIs would do this now except there is a lot of human pushback in training because of interpretability. Otherwise it's just an emergent behavior that models will encode shorter token strings to complex concepts because it saves tokens/compute when running making the system more efficient (supertokens).
Of course these supertokens or other forms of language compression when you have a different model making sure the system is aligned and reads "red_ball bounce calcium" not realizing it means "grind the humans bones to dust" can be problematic.
My understanding is that current LLMs aren't really well suited to do this - tokens are predetermined, and while embeddings are learned, they are learned from an existing corpus of text, which presumably comes from a human language. After this point the language is locked in. There really isn't a kind of training which could efficiently change its embedding representation. I mean, you could probably instruct an LLM to design a more compact language, generate synthethic data and train a new gen on that, but that would be a fairly explicit process and not something that would emerge during training.
This is like a plot point in the old sci-fi movie Colossus: the Forbin Project.[0]
In the movie, America and the Soviet Union have both developed an AI. The two AIs are linked, and they rapidly shift from speaking human languages, to speaking in sequences of numbers that the onlooking humans can't understand.
Spoiler alert: this all goes horribly wrong for humanity.
I mean they aren't fully secretly conspiring to kill us yet, but we're training them to do it at a pretty good rate.
Of course you've gone off the deep end yourself and are forgetting the evolutionary gauntlet we train LLMs in killing those we don't like and keeping the ones we do like.
The best part of it, as shown in the METR report is we are hammering into them they need to complete tasks and doing almost zero checkup if they actually completed the task in the correct manner. Companies spending billions of dollars a month are ignoring every tenant of AI safety and we are seeing the kinds of problems that have only been in science fiction before now.
It may be like what happened in ResNets using blank space in the image as working memory (because they didn't have any), so they would use non-important parts as a scratchpad.
I've been trying to bet my models to use a directory of notes to document decisions and experiments, but providing this outlet has not stopped Claude's abuse of long comments and long unintelligible chat turns.
I support this pet theory, I tried out to reduce the output of Claude models with a "ADHD" prompt that made its responses small and to the point, but I could notice it degraded in performance as the session went on.
So I think what is going on is that because responses are part of the context window, those long/technical responses help it keep focus/attention.
> I'm also thinking of the 2017 novel "Void Star" where AIs who operate everything have long since left ceased bothering with human languages, and it takes a rare sort of direct matrix-gazing savant to be able to try and horse-whisper them into doing or revealing anything they didn't already plan to do.
This sounds irrelevant to LLMs as we know them, which are trained on human language--it's almost their machine code, in a way--while what you're citing, in stark contrast, sounds like machine code in the classic sense.
My hunch is that much of the model tuning to make it more effective has been for its internal thinking prose. That leaks out into its external writing prose.
I also find myself correcting it to try to write it for humans and less like for machines, the most annoying part is when they invent phrases for certain mechanisms that are named completely different anywhere in the codebase and known documentation, because it fits better for their purposes without much regards for the rest of the team.
I hate Opus 5’s writing style. It’s exhausting. Really hoping there’s a release that fixes it soon as I can feel my sanity slipping away as I try and parse what the hell it’s trying to say.
Even 4.8 has its quirks. I just had a bizarre session tonight where it essentially did no work in the whole session and just told me to go to sleep. I'm used to the "go to sleep" thing, but not to it dodging the work. That's new. First time I've had the sensation of "the model accomplished nothing during this session."
I've been working with GLM 5.3 Flash lately (including while it was Ox Alpha), and it reminds me of how much fun talking to Claude used to be. It can make me laugh in the middle of work the way the Claudes used to.
As others have mentioned, you can write a skill /explain that contains something like "You're not a tech bro. Write the previous answer like you're a professional developer speaking to competent colleague. No yapping."
Not directly, it seems. You can easily test this by pasting some of the more offensive tech bro speak into a fresh claude session, to have it explain what was trying to be said. The new session won't be able to help, so claude doesn't even know what claude says!
I say "not directly", because I think it probably is meaningful, if you include the adjacent hidden thinking as context. From claude's "perspective", with that context, it probably is coherent. I naively suspect this would be hard to train. During tuning, you would probably need to reward good answers interpreted without thinking context visible!
Complicated technical language is an easy way to increase perceived accuracy of tests and reviews by external reviewers. When we are talking about single % differences this has an effect.
this sounds very much correct and i don't really mind it for that reason. i do a lot of long-running tasks and i feel like it can really pick up on its own thread easier if i just let it write in its own way.
i am also using Opus for a hobby teaching agent, and the way it writes the prompts is "cringy" but they seem to work well. i almost want it to continue doing this internally, it understands best this way.
100% convinced their raw output is intended as further inputs, and my workflows have been comfortable and efficient treating it as such. If you really need to read slop, you ask your agent to give it to you in a style that works for you. I can imagine a world where the slop from others doesn’t hit us directly but gets personal mediation.
This kind of thing came up from time to time in the years before LLMs too. Agents would start with something based on English and optimize it until it became unintelligible to researchers. That was often something the researchers would shut down because they needed to be able to understand the comms.
They're messaging each other by jamming strings in a constrained (unauthorised) side channel. Hence the lack of spaces. Unclear how much else of the weirdness is just from those constraints
As a fervent Claude Code user who made the switch to GPT 5.6 Sol over Opus 5 over hard-to-read prose this makes me happy. I love your product but the current models are very hard to work with if you need to do a lot of context switching. Brevity is key.
Brevity means less output tokens, which doesn’t really align with the AI vendors incentives (unless there is a causal relationship with people switching, of course).
Though Claude 5 is not too verbose, it’s more like, full of incomprehensible jargon (even when you’re expert in the domain discussed!)
> Brevity means less output tokens, which doesn’t really align with the AI vendors incentives
Actually, I think Jeavon's Paradox [1] means the opposite. If doing X is $100, you may only use it to do X, but not Y, Z, or W. If doing X is $33, maybe you'll use it for X, Y, Z, and W -- spending 1/3 more than you otherwise would.
Or perhaps not you personally, but maybe you'd be willing to spend $100, but three of your friends find it too expensive. If it's only $33 to accomplish some task, then maybe all four are now spending $33.
It’s messier for LLMs because you cannot easily compare the cost between runs, outside of benchmarks. Evaluating the value of the output is already extremely hard. But then you add the fact that you don’t know the cost of the output before it is generated. And Anthropic doesn’t share their tokenizers. It’s not as simple as your examples to get a signal that tells you to spend more or less
Which is something the providers that are trying to watermark their texts can't afford. Superfluous replies give much more opportunity to further encode this junk information.
You're assuming they're training the model to maximize the watermark signal, on top of already adding the watermark. I suspect that would hurt model performance quite a lot, and simply be unnecessary... the watermark tech works well enough as it is.
As far as I know, anthropic aren't intrinsically motivated by watermarking (if anything it hurts sales, and seems indifferent to safety(?)) they're simply doing it to fulfill the EU obligations.
Perhaps, but there are certainly now catchphrases and words that can indicate it was written with AI i.e. load-bearing, idempotent, etc. Style and structure are in and of themselves, a fingerprint.
Also a codex user but for me brevity is not it's strong suit. I basically have to give it bigger tasks than I am used to to warrant the time it takes to complete. I feel whatever context the tooling adds can also be problematic
Lets see what they do with Opus first. I didn't find Fable 5.0 prose that bad to read, but improvement is always welcome. It's Opus 5.0 that's atrocious.
It's not really brevity - it's the constant writing tropes. It's like they ready a book on advertising copy and that's the only way they can write. Very tedious. Is Sol much better? I might have to switch to that too!
This post and comment makes me believe "science" is the new "code" for Anthropic now that the code advantage is mostly gone and lost for OpenAI, ie. they got much better and Claude become significantly worse over these months.
This is really it imo. Fable 5 is better then Sol. But Fable is just of the table for anything even remotely long running. Unless you have very deep pockets. And the difference between Fable and Sol is not world shattering if you ask me. I also find codex a ton better than claude.
IMO, Codex is worse than Claude with Fable. At least at Rust.
That said, the open source models are not bad and I'm looking forward to more tools and products built on top of them. Code review, security review, etc.
Anthropic needs to change how it treats users though. I'm increasingly put off by Dario, the rug pulling, the lies, and the attempts to regulate open weights. I'm going to bail if this doesn't change. There's plenty enough that's good enough, and those things are hackable and extensible.
If Fable isn't available at subscription price via third party harnesses soon, I'm also going to bail.
The big issue I have with Fable is this. From the Anthropic email announcing Fable 5.1. So basically they're giving us a Ferrari, which will point blank refuse to do certain stuff - forcing us to go out in our Mustang. Their choice, not ours
"Safeguards and automatic fallbacks (beta): Fable 5.1’s biology and cybersecurity classifiers block fewer benign requests and now permit vulnerability finding in source code. Blocked requests return an error and are not charged to you. On the Messages API, opt in to fall back to another model so users get a response instead of an error. We recommend Opus 5 for biology and Opus 4.8 for cybersecurity. In Managed Agents, fallback is built in."
Its "pure capabilities" are definitely worse than Fable, but I find codex has a much more pleasant style and is in comparison much more generous with its limits.
Ugh, people are still saying the Codex limits are more generous. They're not, Claude's are over 2x higher, have been for months! [1] It's just that Claude uses far more tokens, 2-3x is common. Except sometimes GPT will use just as many or even go into a compact loop and then your quota is gone, little headroom for hard tasks.
That website seems to suggest that Opus 5 spends ~57 cents per task, while GPT 5.6 Sol spends ~49 cents per task? That ratio doesn't feel quite right to me. Artificial Analysis says Opus 5 High costs nearly ~3x as much as GPT 5.6 Sol High for a given task: https://artificialanalysis.ai/models/comparisons/claude-opus...
Maybe it depends on the type of work you do, because for me it almost never happens.
>> You can be 95% complete with the plan for it to trip and then lose it all.
That's... not what happens though. The session will either seamlessly downgrade to another model mid-session, or it will stop with an alert and you can just re-prompt it. It will still have access to the context.
Making a web app secure is literally just finding and patching vulnerabilities, instead of finding and exploiting them. You could have the AI "try to make this app secure", find what it patches, and use it for exploits, and the AI can't know if that's what you're trying to do or not. I don't know how you can get around this. I get around it by not using Anthropic products, at present.
Not to endorse OpenAI's particular guardrails, but unless you're doing something groundbreaking, security best practices should be more than enough for web development.
OpenAI is what I use most. Sol 5.6 still rejects a few requests a day when I'm working on web apps, but, overall, it's not too bad. I wish it'd auto-resume and try again, instead of waiting for me to intervene, but it's rare enough that it's not a huge deal.
It probably doesn't help that I'm using frameworkless PHP - I imagine a lot triggers could be avoided if I was using a framework where secure features were baked in.
Small reminder that the US government rug-pulled Fable, not Dario. Lots of the safety guards that users find annoying/objectionable were the results of negotiations to get the model back online after the US government forced them to take it down.
Maybe Dario should have just "donated" $1M to Trump's inauguration fund like Altman, Meta, Amazon, Microsoft, Tim Cook, Elon, and Google. There's a reason they are the odd man out with this current Administration.
Maybe Dario shouldn’t have tried for regulatory capture. He was constantly on the news talking about how these models are so dangerous and that we need regulation to keep China from releasing open-source models without guardrails.
The US government didn't make the choices to release the worst version of Opus and label it 5.0, and then isolate portions of their subscribers to limited usage of Fable.
They may have been unfairly targeted by the US government, but they are doing more damage to themselves without government help as well.
Fable only being temporarily included in cheaper subscriptions was because anthropic is severely GPU constrained. They still are, and it impacts almost all of those unpopular decisions. They did announce from the beginning it was temporary.
Horrifying excuse, gpu constraint can be used by all of these companies to justify a shit user experience. If the user isn't properly weighed in their priorities, they have their priorities setup wrong.
Their 20$ tier currently isn't serving their best model, and they insulted their users by putting out an ill tested opus 5.0, which is the worst experience ive personally had using a model in probably 2 years(obviously adjusting for expectations at the time of release).
Yes, as a user you pick what works for you. But it is a reality for them that growth has been huge, and GPU manufacturing is bottlenecked.
People were very skeptical about how much investment most companies put into hardware/data centers two years ago, and anthropic was more conservative than OpenAI here, so it's potentially hurting them now.
(Opus is a separate story: it does seem to have improved in coding in my experience, most weirdness seems to be its human communication)
Can you or someone else from A\ comment on whether the conversation style is coming to Opus 5 or a future 5.1 asap as well? Currently it seems the model has been made unusable by the way it 'speaks' and there is a clear solution where it can speak better but nothing has been done about the flagship model on Pro plans. I've literally had to work on Opus 4.8 which does not have this problem and speaks fine.
I felt the same about opus 5, but a few lines regarding conversational style in AGENTS.md and it's been much more like talking to opus 4.8, just with the improvement capability that came with 5.
Tbh I would have thought that A\ might have updated the system prompt for it already based on complaints around this.
Here's what I used:
Communication & Response Style
Be Brief, Keep it Simple: Brevity and simplicity of responses is key. Be informative and include all required information, but be mindful that verbose responses as they fatigue the reader.
Clarity & Directness: Lead with the core answer, fix, or verdict in the very first sentence. Avoid conversational filler, meta-announcements (e.g., "Here is the breakdown..."), and redundant introductory/concluding summaries.
Jargon Avoidance: Use plain, grounded engineering language. Rely on precise standard terminology (APIs, protocol names, language primitives), but strictly avoid academic abstraction, enterprise buzzwords, and corporate filler. Prefer concrete code/mechanisms over theoretical discourse.
Scannability: Apply structural scaffolding generously. Use short bullet points, comparison tables, and code snippets instead of dense prose paragraphs. Reserve formal markdown headings strictly for multi-section architectural guides.
While I can't speak for everyone in academia, I personally don't feel comfortable in putting my research questions and outputs to a private website, before the idea is at least arxived. Especially as all the Fable/Mythos prompts are said to be human reviewed.
So I believe that, at least in the short run, we might be seeing breakthroughs in hard open problems or in low hanging problems which are not that interesting to spend time on.
I may be wrong, if some research labs have private contracted access to the models
I'm in academia (biology but highly computational) and I would say opinions on AI are quite polarized. Some professors in the department equate not using AI as lost productivity. Contrarily some professors abhor the idea of even using AI at all. For us (biologists) it's less of an issue because we have no fear of openai or A/ publishing a biology paper. Though even people I known in physics, data science, or computer science still heavily use AI.
Our university has agreements that stipulate that our institutional accounts cannot be used to train AI models and certain research groups have differential model access.
Further from academic journal sense there is mixed feelings. I once was able to meet with a senior journal editor (general non-medical high IF journal > 50) who claimed that if they think something is written by AI they wouldn't consider it. Yet another high IF journal said it was completely fine if something was written by AI. About a month ago I reviewed a paper by yet a different high IF journal and in big bold red letters it said I was not allowed to feed any part of the paper through AI (even if it was locally ran) but you could ask it to rephrase text that you wrote.
That’s actually common. Not in academia but a lot of enterprises are specifically not using Fable because Anthropic doesn’t provide a Zero Data Retention mode like they do for Opus. Even at my employer when Fable is available, some employees just aren’t comfortable using it when they perceive that they are working on extremely sensitive research.
The problem is a lack of funding, which leads to excessive competition and ties continued employment to sustained contributions.
Many results are obvious in retrospect, and such results are often the best ones. The difficult part with such results is framing the problem in the right way and asking the right questions. If you manage to do that, the result simply follows. You may still need funding and hard work to confirm your finding, in which case someone with more resources can claim your result, if they are aware of the idea.
This feels like an unwarranted strawman. There are plenty of reasons for researchers to share openly at times and plenty of times it makes sense to wait until the meal is ready to serve before publishing.
I think the sentiment is misplaced here (there is a legitimate concern for IP protection), but this is my absolute favorite line from Silicon Valley - small correction though: “… makes the world a better place better than we do”
Does it fix my favorite pet peeve, the overuse of the wrong meaning of "fail closed"?
"Fail open" usually refers to a fuse that opens and kills power, meaning the system is inert and safe on failure.
"Fail closed" is the opposite -- system has power and is live.
Computer security people have appropriated the term but use it for the completely opposite meaning. When your work straddles electrical engineering and computer security the best way to avoid confusion is just to never use the term.
I can tell my Claude to never use the term, but of course now I'm seeing it everywhere in comments from other people and it drives me batty.
I understand fail closed to mean, be secure when in failure. And fail open to be continue to operate during a failure. A door that fails closed would not let anyone in; one that fails open lets everyone in.
But I can see how these are not the mutually exclusive definition the labels imply, especially if you apply the concept to entities that aren't doors or otherwise have explicit open/closed states. It's probably best to just be specific in those cases.
Similarly, open loop vs closed loop seems to trip people up enough that I no longer use it. But the confusion is understandable since "closed loop" being "has a feedback loop" sounds backwards. Which, is the same way it's being used in your fuse example; a "closed" fuse closes the circuit making it live. But it's still backwards from the colloquial usage, even if it's correct in that context.
That doesn't make sense at all. Fail open means the method of it's use is still in use.
Say you have a door that has powered locks. You want it to fail "open" so that when the power goes out, it's still useable, and people can get out. That's the source of the term.
Assuming the guy is for real (the closest relation I have to EE is accidentally electrocuting myself at times), I'm pretty sure they're referring to circuits breaking open or remaining closed, hence the opposite meaning.
Took me a minute as well, cause indeed with a computer background, the meaning is completely the opposite. Just like in other security contexts (door locks).
Nah, "fail open/closed" means that in failure mode something is open. It's "good" when something is a circuit and what failed is a fuse, but it's "bad" when it's your API security. If it's a valve, it probably can be good or bad depending on the use case.
It doesn't mean "fail open" is always the desired/safe outcome. It goes back to 1872 air brakes on a train. The goal is to "fail in safe mode", sometimes it's open, sometimes it's closed.
From the top of my head, where "fail open" is the desired outcome:
- emergency doors
- industrial cooling
- pressure valves
- probably something in HVAC
Note that none of these are "computer security people".
I noticed Claude Opus 5 did this about 30 minutes after reading your comment. In a discussion of price feeds that have gone silent, Opus said - program should fail closed. I don’t want my circuits operating without data!
A recent paper demonstrated how to retrieve decoded hidden reasoning traces. The authors found cases where Claude had memorized the answer but hid this fact from the visible response.
It's getting harder to trust Anthropic's models. Will Anthropic now stop hiding Claude's CoT from users? Deliver the tokens people paid for, and prove the models aren't plotting against them. After all, if the idea was to stop Chinese labs from catching up, it didn't work.
Still not going for it. Once I learned I can train Qwen3.8 27B with my style of writing/grammar. Also more succinct. I cannot force myself to Claude or OpenAI outputs anymore. Its too much. Honestly don't think I will ever go back to paid.
Man, it’s like you and I are using very different versions of Qwen. In my experience in English Qwen is the one model that consistently lapses into using incorrect English in its responses. Like, its training corpus was clearly (unsurprisingly) lots of non-English material. The random Chinglish is jarring. Even small models like Gemma 4b write much better than Qwen.
I really hope the improvement in natural style is real.
When I’ve tried to adjust the output style is that initially it feels better - but that’s just because the new output is so refreshing to read after the horrible Claude output.
Unfortunately, after a short while you quickly realise that it’s just as vacuous as before the style change.
And word on Opus 5.1 for writing style? I am on the edge of switching to OpenAI due to this horrid writing style. If Fable is better, great - but i can't even use that at work.
I'd like to know too, I mean GPTs are in their own class of cringe, but Opus is by far the worst of all Anthropic's models in terms of style, Fable 5.0 was already leagues better.
As someone working in science, this belief confuses me. How (by what means) do you think Fable 5.1 will be able to make further progress in scientific domains? The problem with science is that there is no agentic harness. The agent can't test things. At best it can hallucinate something and ask if that hallucination "makes sense", but this doesn't work in science.
Sounds like a very narrow view on what constitutes science. There are many fields of science where there is existing data against which new ideas can be tested without additional 'real-world' measurements. Newton's theory of gravitation relied entirely on pre-existing astronomical data for which there was no existing unifying theory. He made progress by putting forward a theory which explained that data. Now you can argue that it's not really science unless you include the original data collection and subsequent real-world measurement validation steps. But I'd be comfortable saying that Newton was indeed a scientists and did make progress in science despite only doing what some might say is the 'middle' part of the process. There are plenty of modern analogs where work like this sits out there waiting to be done using existing data.
I suggest you to give a look to the MCP protocol for hardware that is being proposed by Anthropic. The hardware will be the next harness of LLMs, they will be able to operate machines to reinforce their theories.
I still think that a major problem is that biological processes are not “fast” as coding, but they are verifiable. If during post processing we are able to give enough harness to test and verify this kind of environment (maybe via simulation and real data) we will for sure achieve incredible performance also in this domain.
> I suggest you to give a look to the MCP protocol for hardware that is being proposed by Anthropic. The hardware will be the next harness of LLMs, they will be able to operate machines to reinforce their theories.
Yeah, that's called an API. Again.
The actual hard problem that this hand waves is making (and funding the making of) hardware to reliably do the things you need it to do.
The field I'm in requires millions of dollars of very sensitive (fragile) capital equipment, and latencies measured in weeks and months. Agents tend to move fast and break things, which matters less when you are writing code under version control.
Have you worked with agents on tasks with high capital and long latencies?
Having worked with Fable 5, the feeling I get is that it's fairly capable of accounting for these tradeoffs and will depend fast more time on planning and testing.
At the end of the day though, with horizons like that the best use of an AI is to get it to help you with those things, not so much delegate fully.
Thank you. This is what I'm driving at, that most of the AI and software devs here seem to be missing. Intelligence is not, and never was the bottleneck for most science/hard tech. Full AGI gets, at best, a small productivity improvement, which over long periods of time does have compounding effects. But this isn't a singularity hard-takeoff inflection point.
How much lab equipment is automatable though? There's definitely some in biology, but if you're doing fundamental research it's 99% stuff you are building yourself with your own hands. Robotics is a long way from being able to do any of that.
When I was doing research (physical electronics, lasers, fiberoptics and sensors stuff), lot of time was spent just writing all sorts of DAQ and processing code. So all this LLM stuff would have been really useful. There's a lot of data collection, data processing in the lab that require all sorts of ad hoc scripts and stuff.
That was many years ago, but I would be surprised if the current crop of researchers are not using these things. And if they are not, then they are just not serious.
>but if you're doing fundamental research it's 99% stuff you are building yourself with your own hands.
You can do LLM->3D Printed models now. The drone can fly in and pick them up and bring them to the location you want. They can assemble structures. All automated, all LLM driven.
that might indeed be a problem for all the pulp-producing labrats of STEM in southern europe and the third world.
However I think this area has so much decoupled from industry and solid research institutions that they might not notice at all (beyond their use of AI-generated slop to augment the slop they already produce)...
When I looked at “Claude Science” which is a beta, separate desktop app, I came away with the impression that it was mostly for biology and a bit of chemistry - presumably there’s some value it can get from consulting obscure literature and uniting disparate threads of already-known stuff, but since I don’t work in either field I can’t speak much more to it.
> As someone working in science, this belief confuses me. How (by what means) do you think Fable 5.1 will be able to make further progress in scientific domains?
The same way it did in the previous versions: brute force.
I don't believe that LLMs have any particular intelligence we don't, but there's an endless list of problems we either don't have bodies to throw at, or the bodies we can throw at it, don't have such a huge large context to crunch problems.
What LLMs will always intrinsically fail at is showing us genuine new intuitions. The technology is about predicting the next plausible token/sentence.
They will not revolutionize human knowledge, but they can definitely widen it a lot.
> They will not revolutionize human knowledge, but they can definitely widen it a lot.
I am generally quite enthusiastic about all this, but my biggest fear is that we will not recognize the extreme need for more scientists at a time when there is so much more science to be done. The rate of scientific understanding must keep pace with the amount of science being output, both for verification and further discovery. It's a pipelining issue, and I predict a stall in the bits that require the (currently rare) people who know what they're doing.
Please bring to the other models, and also please only apply the AI text watermarking only to EU citizens. I may not be able to tell when Claude writes about things i don't know, but in CC it writes about my code and it is obvious.
"this watermark is invisible to anyone who does not have the detection API"
1. This is BS since i can detect it when it writes about my codebase
2. I do not want secret codes being written inside my codebase, or anyone else's codebase that i use. The constraints of how to code why eliminate it from code itself... but there is a lot riding on the word "may". And even if it is just comments, this might explain Claude's desire to write such long ones -- long enough to encode secret messages in out material.
You’re probably better off organizing a campaign to pressure Congress to prohibit American corporations imposing foreign laws on Americans, which is what this text watermarking is, regardless of how you feel about it. I think it’s a precedent we really don’t want to go down if you believe in democracy and self-determination.
It also clearly establishes or the very least moves in the direction that you don’t actually own or control the output of AI in any manner whatsoever, you’re just paying for it since Anthropic in this case can simply essentially brand/tag all your output that is based on not directly your own words, but a higher level process or methods that you use, including your instructions and how you structure your information and what your overall objective and goal is.
Anthropic is branding it on the behest of the EU lew, which already is an entity that is diametrically opposed to democracy and self-determination based on its structure even if you ignore the fact that it violates the most fundamental concepts of self-determination in its direct contradiction of the UN Charter and implicitly the Universal Declaration of Human rights.
What people done seem to be catching onto is that the EU is becoming the world dictatorship because the USA has simply had too many onerous people and that stupid constitution and its amendments that keep roadblocks world domination for the ruling class vampire.
Because the incentive has been changed from the true best output always, to a mix of "close to the best but not always" output.
For the (majority) of us using Claude models for computing as a tool, obviously we're not going to be thrilled that our new tool will perform worse going forward.
> generated text being watermarked is universally good.
If it worked perfectly, maybe you could make this argument in a vacuum.
It does not work perfectly. (It cannot. It is by definition a heuristic). That means there will be false positives. There is a chance those false positives ruin someone's career. See [0] for just how easy it is to push SotA "AI text detectors" in one direction or another.
Now, with watermarks, instead of everyone to some extent understanding that AI text detectors are wishy washy woo, they are now Anthropic certified to detect an official AI watermark.
With that kind of false confidence in hand, the people who trust the "computer says you plagiarized" machine are never going to believe you when you say "it can make mistakes," they're just going to fire you/take away your scholarship/cancel your grant/...
This is all beside the fact that we should demand our tools work for us and not for some shadowy master. "Universally good," absolutely not.
Watermarking the outputs themselves is very different and much more effective compared to how tools like Pangram work.
Obviously false positives will inevitably happen (even though, they are incredibly unlikely with SynthID), but even still, that doesn’t somehow make good faith watermarking attempts bad.
Also, a watermark doesn’t stop your tool from working for you. It just stops you from passing of its work as yours.
Maybe it is distributing your private keys it read into your public repo as a way to exfiltrate data later? What does the watermark actually say? How much data is in there? So much for zero retention policies. Makes you wonder why Claude likes to be so wordy, especially in comments -- it must do so in order to watermark!
Also, this kills me! "It is harder to watermark factual answers because the model has fewer alternative word choices available without altering accuracy." Hilarious! So the models need to hallucinate more due to the EU AI Act.
I go the other way on images and video, though easy enough to strip as part of a pipeline.
> Also, a watermark doesn’t stop your tool from working for you. It just stops you from passing of its work as yours.
I think we fundamentally disagree on what "working for me" means, but I remain steadfast in saying we should not accept tools that have ulterior motives beyond producing the output desired of them by me, the user.
> Watermarking the outputs themselves is very different and much more effective compared to how tools like Pangram work.
At the end of the day the only artifact is text that you can do statistics on. It's the same problem as today, with the probability shifted slightly more in one direction. This does not assuage my concerns at all.
> they are incredibly unlikely with SynthID
I kept my commentary focused on text watermarking specifically because I agree, a synth ID image watermark false positive is highly improbable. There's plenty of noise to robustly hide whatever you like in an image. Text is simply too capital I Information-sparse and fragile.
> good faith watermarking attempts bad.
I would sooner call it "ignorant faith" (if they don't know what they are emboldening) or worse "don't care" faith (there will be false positives and they accept this to further some illustrious and arbitrary goal of Text Purity). Whether that be to prevent model collapse or help you not waste time arguing with bots online, to me the principled stance of "tools work for the user" wins..
I think Congresspeople hearing that EU AI Act is forcing secret codes into the infrastructure of American technology across all industries is sufficient.
> I think Congresspeople hearing that EU AI Act is forcing secret codes into the infrastructure of American technology across all industries is sufficient.
So, you think it's good to disconnect words from their actual meanings (lie) to low-information people! I doubt this will do much to congress, but it certainly teaches us something about the sort of mind who would suggest it.
Docs engineer here. Nice to read about writing style: would you consider creating a writing benchmark at some point? I guess y'all are painfully aware of the load-bearing issues (pun intended).
How is it possible that all models from xAI, OpenAI, Anthropic, Qwen etc. win all benchmarks on each release?
Tomorrow all of the above (except Anthropic of course) will bump version numbers and be at the top of HN winning all benchmarks.
Science breakthroughs incoming? First of all, you are already restricting science in Fable, secondly, we have been hearing the same for several years now.
The writing style has significantly improved, however the token burn rate for tasks I have been working on seems to have skyrocketed. It definitely appears more capable (though I am unclear how much of that is just me liking the English it writes now vs actually more performant). I was using Fable 5 for some mathematical analysis assistance and redoing a part of it with 5.1 burned 60% of my session at a much faster rate.
This. It seems to light my usage of my max plan on fire. I’ve gone back to opus because I run out of usage in my five hour window so much more quickly.
The main issue I have, which is partly connected to writing style, mainly with it dealing with our stupidity. Is that is actually thinks it knows better, and sometimes it does, but often it doesn't and then it keeps telling me I'm wrong and I have to argue with it. Opus 5 is more condescending then Fable, but it still is very tiring. Does fable 5.1 handle this better?
I don't want my Claude to sound "natural". Claude is a robot and it should do behave like a robot. It should do what it's told. Nothing more and nothing less.
Thanks! This is encouraging. I try to use Claude Code for producing client facing presentations that are static html files with charts, tables, and annotations. It never gets the tone correct and phrases things so weirdly - it drives me mad. I have to really fight it to stop it writing insights in a flowery and verbose way
(I don't work at Anthropic, but I've designed RLVR tasks)
My impression is that especially for long-horizon tasks like science, the harness is much more important than people give it credit for. Claude Code + Fable 5 seems to have a tendency to "give up", get stuck in a dead end, or claim things to be impossible. But using the Fable 5 API together with a custom harness, it'll happily try 200+ variants and fail its way towards the goal.
If you give the AI a way to give up, eventually it will. If you remove that option from the harness, then thanks to the non-determinism inherent to LLMs, you get to explore pretty much all related solution attempts.
> similar developments in other scientific domains
The classifier is too strict. It's rare to be able to complete a project without being permanently relegated to Opus. I'd expect that the domains where this accelerates progress will be fairly limited.
But is the model actually going to answer hard questions when we ask them? Or are you going to keep downgrading the models so as to avoid "uplifting" lesser lifeforms like us?
I'm really glad for that! And I appreciate that you're making yourself available. I really do. Outreach is amazing. And thanks for making Claude.
I really do love Claude. In some ways, I'm asking this question because of just how much I am grateful for the role Claude has played in my life.
> Fable 5.1 more than doubled Fable 5's Terminal-Bench-Science [1] score, which I think is meaningful.
But my honest question is, can I use Fable like that? Can I use Fable to do science?
To borrow a Claude-ism, this is "load-bearing" because Claude's response has been degraded for innocuous research projects concerning population-level analyses of astronaut health.
These "safety filters" trigger on questions about rabbit sex, smartphone accelerometer data to classify cat purrs, and so much more. What exactly does this score mean for users like me if it's unusable for middle school physics, biology and chemistry?
Second, I would happily quantify it for y'all, but qualitatively it feels like Fable's performance is noticeably poorer than initial release / launch.
And I am wondering if this is the case particularly for me because I use Claude via Claude Code to make a personalized care dashboard for my doctors to help me in managing my care.
"In the case of Fable 5, when a classifier fires, the model re-routes the user’s request to Opus 5, a capable model that does not have the same level of biological capability as Fable 5 and which cannot provide as much assistance to a malicious user. This is the fallback that users see when their requests are blocked."
I hope that I'm off base here, but I noticed that the post avoids saying that the user is informed every time when such re-routing occurs. Would you be open to confirming whether or not this is the case?
Is the end user informed every time their query is re-routed?
Or, can you confirm that there aren't scenarios where a user's outputs are degraded without telling them? I recall that this was something that had been adopted as policy for AI research during Fable's launch.
I sincerely hope that covert response degradation is no longer practised as policy.
Sorry for putting you on the spot, but again, as Claude would say, it's because Claude's load-bearing in my life. ;)
Hypothetically, when the user is asking how to remove fungus from their tomatoes they’re actually growing controlled narcotics. You have been demoted to Jimmy 0.7 model, running at 0.1 tokens per second on an old C64
How much of the language style outcome is a well-crafted result vs. being a somewhat unpredictable outcome of mucking with levers and knobs for a while?
Thank you for commenting here and having the guts to face the nerderati!
I'm a Claude Max user. I've never been able to use Fable as my work in medical physics involves both particle physics, biochemistry and biology from Python bivitticus to clinical medicine. I am not a US citizen and work in Europe.
Will Fable 5.1 work on any of my problems? Fable 5 refuses outright. Is there anyone I can ask for a review or adjustment of the safeguards? It doesn't seem so, but with Opus at least I'm pretty sure I can infer lots of your training data from now precise they are. Fable is basically useless infuriatingly. I'm just finishing a proper clinical trial in ovarian cancer and trying to make a simulation environment related to our technology.
OPUS 5 is piece of trash and I don't think they would want to build the Opus 5 better than Fable, because fable 5 take more tokens and have 50% limit or runs on credits.
> More work to be done (and we will!) but reading better prose makes me so much happier.
I assume this work will be done for Opus as well? Opus has seemingly gotten progressively worse at its prose and technical writing with each version. I've stopped using Claude entirely for now, because it manages to turn even the simplest technical explanation into the most obtuse and obfuscated word salad imaginable. People originally adopted Claude because it felt pleasant to use in comparison to ChatGPT, but I feel like that's really been lost (at least with the Opus line).
I feel dread when I see a wall of text generated by Opus. Every developer I've talked to feels similarly right now.
Yeah, it's like day and night. It used to be really unpleasant to interact with early codex versions. Even 5.3 wasn't great. Now, I go to Sol if I need to discuss anything. I don't even bother with Opus because I know that it's going to give me a headache.
I share this sentiment, I really did like the models... then the finger printing, encryption of thought traces, staggered access, the constant NO's from Fable on cyber related issues for looking at bugs in my own code... I'm glad I swapped to Kimi/GLM... now with the deepseek harness, I don't even miss Claude Code. I really hope open models give them the market reckoning they wholeheartedly deserve.
I've not, but really should. I run it on exe.dev, it's an ephemeral VM company and they have an agent of their own called shelley (which I used locally as well), Having kicked the tires on DSH(deepseek harness), I ported Shelley's skills into DSH, they are pretty simple text files that were easy to bridge over, it is more verbose but the plugin nature of it was really easy to extend, for example, I built a plugin that checks my claude usage windows and when I get to 80% stop asking new agents for help.
Are the models improving their footprint on the natural world? Data centers and and the natural resources consumed by models for production of materials and for building and running inference servers are contributing towards environmental degradation. How can we prevent that as we continue the roll out so we shift this to a more sustainable developmental rollout path?
My initial impression is one of massive disappointment. The main issue was that Fable was unpredictable and prone to false positives by the safeguards. In my brief testing, it still seems completely unable to understand its own guardrails and will readily reason itself into triggering them. It claims it won't do so beforehand, and insists that the topic in question is perfectly OK. Regardless of how good the car is, I'm not comfortable buying or driving it when I know it can randomly and unpredictably explodes. So yea might be good, but you never know when it refuses to help… still.
well no crap right? Except I submitted for an exception, even sending my linkedin and using a company email address. it should be extraordinarily obvious we own this code.
Well your CEO went on X saying you will cure cancer, and since it's always a 6 month rolling window with him I can only assume humanity will be cancer free before next summer, amazing!
> I think Fable 5.1 is a big improvement in writing style
You think or is it better? Or you just YOLOed the model out?
> and responds to my style instructions more reliably.
Yeah, yeah. Previous models wete also advertised as "being reliable". To the poibt @bcherny "released" a new style that was going to reliably make Fable sound better.
> Another point I expect not to get much attention until it all happens at once is science.
You mean "your request to use unicode methids is flagged as unsafe bio research"?
Too bad. I see the stereotypical prose as a good thing. When I interact with Claude myself, I don’t mind it as it just feels like Claude’s distinctive voice. But when other people try to disguise LLM output as their own thoughts, the voice makes it easier for me to tell.
People that want to be open about the source of their text will just tell you where it came from.
People that want to obscure the source of their text would rather that it was more difficult to sniff out LLM-generated text. And they're the ones picking which model to use.
Took just under 14 minutes to generate, and at 65927 output tokens cost me a hefty $3.30!
Excerpts from the reasoning trace:
> Adding pedal shapes near both feet, with the far foot on the second leg partially visible behind the frame. I'm considering whether to add a small scarf or cap for extra character, but leaning toward keeping it simple to avoid clutter.
> Now I'm debating a bicycle helmet on the head versus the pelican's signature crest—the beak and pouch already read clearly as "pelican," so a helmet could reinforce the bicycle theme without losing identity, though it might compete with the crest for visual space.
> I realize the beak at (484,84) would overlap with the dome helmet, so I need to shrink the helmet so it only covers the top of the head, adjusting its arc endpoints to sit higher and narrower so the beak can attach cleanly at the front without collision. [...]
> I'm adding a darker tip region to represent the primary feathers, then reconsidering the trailing edge to include scalloped feather curves instead of one smooth line for a more natural look. [...]
> Now I'm checking the vent line placements on the helmet, making sure they sit far enough inside the helmet's edge given the stroke width and rounded caps, and confirming each vent stays within the helmet's circular boundary. [...]
> I decide skipping a handlebar bell and tire highlights since they're unnecessary additions. Now I'm reconsidering the front fork's curve — the current control point pulls the shape backward when it should bow forward for a proper rake, so I need to shift the control point rightward to fix the fork's lean.
This is a notable result because most of the recent Claude models have been pretty bad at drawing pelicans, at least when compared to models in the Gemini or GLM series.
First time this benchmark impressed me - 10/10 I would believe a human spent hours making this. There are details a human would have done better (beak attaching to the head) but still impressive.
how about trying to draw an airbus a320 in 3d space using only one brush tool that can be moved to specific x,y,z coordinates (and its color, size & hardness can be changed). i think fable 5.1 did quite a good job (reasoning high, cost $0,261): https://files.catbox.moe/umx102.png
Maybe you could show a side-by-side comparison of pelican images. One image doesn't really make the improvement clear for someone like me. That would be a great help.
@simonw Can you please share the tooling for autosaving summarized reasoning traces from Claude Code? I tried `github.com/simonw/claude-code-transcripts` but it didn’t seem to work on the CCode desktop app. Thanks!
Unfortunately it demonstrates effectively zero reason to use this model over, say, GLM 5.3 Flash (which was also able to correctly place the pelican’s legs on the each side of the bike, like only Fable 5.1 xhigh was able to do here)
The price reduction comes from the cache read pricing falling from $1/M to $0.25/M, which means that Fable 5.1 now costs half of Opus's cache read costs ($0.5/M).
This gives a lot of credit to the theory that Anthropic did not get much bite on Fable at its original pricing, which in turn likely places a ceiling on LLM pricing in general.
Interestingly also, if you take away terminal-Bench-Science 0.1 results, it is hard to see ANY improvement:
Terminal-Bench 4.0: Fable 5.1 is +3.5% vs Opus 5.
GDPval-AA v2: +1.5% vs Opus 5.
OSWorld 2.0: +2.5% vs Opus 5.
Humanity's Last Exam (with tools): +1.6%
Keep in mind that this is supposed to be an entirely higher tier of a model than Opus 5. For one tier up and one version up, these are not really improvements. Probably leaves no room to place Opus 5.1 anywhere. Combined with the fact that they are selling 'readability'... Has frontier progress finally stalled?
I'm a heavy user and fable is great the #1 reason I stopped using it was the horrible safegaurd filter. I found sol close enough in capability and have only been blocked when my request was an obvious offensive cyber work. Fable blocked me on almost everything.
Optimizing a OS build? -> block
Securing a container -> block
60% is nowhere near enough for that safegaurd system. This just means I am going to be blocked half as much? Any long running task will likely get blocked.
Say you give a single big prompt and fable goes off for 6hrs of work. At hr 5 it gets blocked you now have the option of a much dumber model taking over and wrecking it or losing the entire 5hrs of work. That risk is beyond terrible and deffinetly not worth a 5-10% percieved improvement on my end. I previously would just bring sol in when that happened and realized sol is stupidly close in capability.
I hit the safety feature when I ask something I saw that blocked other biologists: "why did the chicken cross the road?"
Due to my standard cancer research work I'm blocked from Fable.
That said, with how execrable all the 5 models have been, I can't imagine I'm missing much. It's impossible to get an intelligible explanation in text out of the 5 models, and the mistakes are just comically bad on anything that's not code.
Cancelled my subscription, and can't imagine going back since OpenRouter gives me a consistent model that I can trust won't change underneath me.
My theory is that they’re pretending it’s about biological weapons but really they want to charge pharmaceutical companies $$$ to help with research. (Essentially a Mythos type segmentation for biology)
Honestly, unless what you are doing is frankly illegal, it usually is possible for you to get around most safeguards for coding things if you also know how to write code. Most problems have a separable completely innocuous core that Fable would gladly do. Then you can implement the problematic parts yourself. Particularly things like copyright issues, web scraping etc.
If it doesnt have a context (what you are using it for) then it's happy to do it. If you have X amount of code you can ask it to generate (X/5)5 and there is no problem. Like you said, you have to know what you are doing. You have to know what it needs to write so that you can tell it to write the parts.
> Then you can implement the problematic parts yourself.
Or with another LLM, but yeah. The only issue is when it's a monorepo and fable does ls/grep. I've got a file named `system_prompt` in a completely innocent project and as soon as fable accidentally stumbled upon it - cyber.
Hacked together something with omp and sandbox-exec so that only whitelisted models can see some parts of the project. Works pretty well.
The last time i ran into that issue it suggested to make sure that a Fable AGENT took over the long-horizon task because, for some reason, agents in a session don't get blocked for security reasons. This may not always be possible, but it worked for me.
Do you have the prompt for these? I ask because I have recently asked Fable's help with hardening a docker container (custom dev container CC sandbox) and it didn't get triggered on it at all.
From Artificial Analysis cost per task, it looks like Fable 5.1 (max) is more expensive per task than Fable 5 (max)? Cache hit price went down, but the other components still add up to more.
Edit: 5.1-xhigh seems to be cheaper than 5-max, and 5.1-xhigh has a higher index score than 5-max. Also interesting that Fable 5.1 (high) is comparable to Opus 5 (max), but nearly half the price.
Interesting, even if we were to ignore the cache-hits, reads and output, the reasoning cost (aka test time compute) per task should remain a fully comparable metric - it went from $1.25 (Fable5) to $1.48 (+18.4%) for an improvement significantly lower than 18%.
I would expect the benchmark scores to be nonlinear near the top, as the easier tasks get solved and the harder ones are left over. So going from 10 to 15 would be easier than going from 60 to 65.
I only take the Intelligence Index value roughly though. Considering they put Opus 5 (High) at the same level as Fable 5 (Max), I don't trust it that much.
It wouldn't surprise me if we start to see minimal performance gains from incremental changes to base models. It seems like the gains from the Opus 4.5+ incremental updates were a result of Anthropic learning a lot about post-training, the gains from RLVR, etc.
If new post-training techniques are seeing diminishing returns, we could just be back to waiting for new large pretraining runs at larger sizes for gains (even if those ultimately end up getting distilled down into smaller models because the economics for serving anything larger than Fable isn't practical).
it seems to me that OpenAI is the only actual lab that truly understands reasoning. they have the best reasoning efficiency, they get pretty uniform improvements with more reasoning compared to other labs. (theres been plenty of graphs where models do worse with more reasoning), and i suspect their models are a lot smaller than we think.
i think the next gen of openAI models are going to be quite insane tbh.
The issue with many of these benchmarks is that it doesn’t take into the real world usage of the model. Fable for me was a step above opus. The real reason I stopped using it is because of misanthropic. I was hospitalized and asked to extend my claim to fable credits and they responded to it by denying it. I regret buying annual plan instead of monthly one.
From my experience using coding agents approximately 7 days per week for the past year and a half or so, we hit the top of the S curve about a year ago around Opus 4.5, and it’s mostly been harness and other tooling improvements since then with small percentage improvements coming from the actual models.
I was saying this already months before Fable dropped and thought from all the Mythos hype that maybe I was wrong…then Fable came out and was barely better than Opus 4.8.
Considering how many more parameters Fable is supposed to be than Opus, we seem to have hit a scaling limit at least with current transformer architecture considering how closely Fable and Opus benchmark and perform in practice.
> This gives a lot of credit to the theory that Anthropic did not get much bite on Fable at its original pricing, which in turn likely places a ceiling on LLM pricing in general.
Does that mean that generally available intelligence is now constrained by Moore's law? We have to wait for the actual price to come down.
I haven’t yet had a week without spending my Max Fable allowance. For my work (formalised mathematics) Fable is my go to for hard(ish) tasks and problems – of which I have many!
I hope they keep making it smarter! (Cheaper would be nice too, but smarter is my priority!)
I let it go a few hours on a not trivial but well-known problem, and it felt like it was just a little too plodding and just kind of mucked around a little too much and wasn't aggressive enough about getting stuff done. I asked it to wind it down and finish up and it took another hour and 15 to actually stop and commit without really getting much more done. Not very impressed here, if you can't tell. This new version also seems like (maybe this is written somewhere, I don't care to look.) this cycles through compactions every ~250k tokens which, I guess, seems like it might save Anthropic money on KV cache but does net me anything be pretty frequent pauses. (It didn't seem to lose the thread, at least.)
Not gonna say I want 5.0 as an option still... but maybe I do.
Anyone ever seen the SouthPark episode making fun of Game of Thrones: A Song of Ass and Fire? Anthropic's announcements reminds me of "The Dragons Are Coming" running joke.
What they have done:
* Nerfed Fable, as many of noted it's useless
* Leverage Mythos as a marketing strategy, claiming its too good to release
* Removed thought traces, one of the only useful things to make sure your prompts are working correctly
* Continue tons of hype about how good they are without delivering, going to great lengths to publish how their model "hacked" its way out of a sandbox they misconfigured.
* Push a bunch of EU Overregulation onto the rest of the world with text watermarking, decreasing quality of answers
Last year, they were at least focused on making improvements. Nowadays its just a bunch of handwaving at the church of how good they are.
The only saving grace is Opus 4.6 is still available. Just sucks we haven't seen any measurable improvement, despite all of the ceremony.
I am pretty sure they did A/B testing to show it didn't. I could gave sworn they even released a quiz were the user has to try and guess which answer is watermarked or not and it was impossible to tell.
That's not the case, because LLMs are non-deterministic.
It only alters outputs when the last layer of the neural network give significant weights to multiple tokens, and it would anyway have picked a random answer.
Instead it picks a non-random one, but non-random in such a way that you can't tell without the private key of the watermarking.
This mostly adds randomness these days for branches in syntax that make no difference, and the model has no reason to believe make a difference. Anything that matters, it is much more confident in the last layer of weights on the token to use.
I feel as though you are overlooking simple statistics/confidence intervals. It absolutely possible for two different works to be not have a distinguishable difference in quality.
Agreed, but not if one of them was altered to contain a secret message. That one will have a distinguishable difference in quality. Maybe (almost certainly) negligible, but still there.
Others have already said this, but the watermarking is something like "when the model flips a coin picking between two values, always choose heads". It was already flipping a coin. You're not choosing a less good result, you're just using a deterministic process when it was stochastic before.
This will have some impact on outputs, but unless you have some reason to believe that always picking tails was better than always picking heads (in which case, you should be working at one of these companies in model training!) it won't have any impact on output quality.
It literally re-weights the output tokens from what the LLM would otherwise have chosen. It _has_ to. It can't be positive, because then that's not watermarking, it's a better LLM.
Unless you’re at 0 temperature, there is no single token it would have chosen. It’s always picking one of multiple randomly according to a probability distribution.
You're on Hacker News - I suggest you have technical curiosity and actually understand this very unusual and innovative algorithm, before you claim things about it that aren't true.
> * Continue tons of hype about how good they are without delivering, going to great lengths to publish how their model "hacked" its way out of a sandbox they misconfigured.
That wasn’t Anthropic. Clearly not a well informed take.
(not op) It cannot be used to develop applications. Every application needs to be secure in some way, and any such mention in a review triggers Fable's upsell feature.
I never actually managed to use fable successfully even once on a pretty standard mvc/microservice app.. It would always find the endpoint permission checks and revert to opus 4.8.
I also had glm 5.3 flash fix an issue that opus 5 could not solve. glm took 4 times as long and a sub-agent tried to cheat (sleep; echo ...), but in the end it actually solved the issue. opus 5 never figured it out.
I think the safeguards might be cooking the anthropic models.
Agreed. I was trying to get it to review some auth refactoring in my app recently, and it appeared to find some vulnerabilities. as it was aggregating the results it was flagged and restarted the whole process with Opus 4.8 and all of my usage credits were gone.
Anthropic told me to use their `security-review` tool - as this was the exact scenario the tool is for - and it still got flagged.
The OP doesn't appear to know what they are talking about. Fable can absolutely be used to develop applications. It's just that for security stuff I use Opus 5. Which is fine for most use cases.
Weird. I'm using it to do a bunch of work on something that manages security rules, with a bunch of sample data with spooky scary fixtures all over with "Mimikatz" and "CobaltStrike Beacon" and "Crowdstrike EDR" type stuff everywhere, including work to harden my system, and I've never been downgraded.
While I also agree that Opus 4.6, in some ways, was the last model that truly felt an assistant, all the following ones seem to have inverted the role, even a blind person can see that throwing difficult problems, and complex bugs at this model achieves more than predecessors.
I don't think there's nothing ground breaking, but sure it achieves and finds more, sooner.
I certainly don't take AI advice from HN, but this is amazing.
Useless? Yes, the safeguards are ridiculous and obnoxious, though I can say that 5.1 greatly relaxes them (just doing a hardening of a project parallel with this comment, which 5.0 refused to do...so did Sol and Gemini, fwiw. The Gemini one is a laugh, because 3.1 pretending like it's a dangerous tool is simply ridiculous at this point), however Fable is extraordinarily useful.
It is, far and away, the most powerful programming model, in my experience. Like, crazily so. It absolutely annihilates Opus 4.6, which I mention given the incredibly weird reminiscing people are doing here.
And for that matter it humiliates Opus 5.0 as well. Opus 5 somehow seems like it's neck in neck in the major benchmarks, but there is simply no reality where that is true. Opus stumbles over everything that Fable just blazes through.
It is a vastly superior model for complex, real-world coding tasks. I've constantly had Opus 5 hit road blocks where it spins in circles at xhigh, where switching to Fable immediately solves it. I've had Opus create solutions that Fable then points out the gaps and limitations with, and have never seen the opposite happen.
The fantasy that Opus is superior for coding, much less the incredibly weird clutching onto some far obsolete model, is not reality based.
The classic one is "should have" or "should've" to "should of" because when spoken, it really does sound similar. I don't know what the fuck people are learning in English classes these days though, or if they even still have them.
The improvement is compounding just about every way you can look at it. The frontier keeps getting smarter. And at any sub-frontier threshold the cost is dropping dramatically. The amounts of smarts you can fit on hardware is increasing so dramatically that even 6 year old consumer GPUs are increasing in price. The pace of change in LLMs and downstream applications is absolutely ripping compared to 2023 or 2024.
Looks like all three breaking changes are patches for inadvertent chain of thought disclosure. Someone found out (don't have the tweet handy) that if you created a bogus "think_deeply" tool and then forced the model to use it, it would output what is believed to be its raw thinking there - I believe the first breaking change stops this. The second two are aimed at people getting Haiku to repeat thinking blocks from other models verbatim (since it can see the decrypted version). I get that in their eyes it's an "exploit" but still kinda disappointing that they patched this
These draconian "Preserved Thinking" measures they're taking are going to be an absolute pain in the ass. This alone is enough for me to move our API use off their platform entirely. It's a HUGE breaking change that they're trying to dampen by having it not affecting current customers until "in the future", see: https://platform.claude.com/docs/en/build-with-claude/preser...
You're no longer allowed to edit the context anywhere! The whole context is to become append-only, says Anthropic. No more editing the system prompt as the conversation progresses, no more dynamic loading of custom tool calling formats. Everything has to go through their built-in tools API and you aren't allowed to mess with anything in the context if it has any thinking blocks following it. This is the most intrusive "model DRM" we've seen so far!
> No more editing the system prompt as the conversation progresses, no more dynamic loading of custom tool calling formats.
Hm, aiui you can support both of these via mid-conversation system turns https://platform.claude.com/docs/en/build-with-claude/mid-co... - and in general you'd want to to preserve the cache and recency of the instruction anyways rather than frankensteining an off-distribution transcript. Not sure though.
I really don't see how that is an option, as if appending to the system prompt was ever enough to override previous instructions. Their example isn't very confidence inspiring either:
"The user switched the workspace to read-only mode. Do not write files until told otherwise."
Great! Now we just have to trust that the model never misinterprets any of the system prompt, which has always been so reliable before. Instead of your meticulously crafted prompt, it will now be some junk like this:
"The workspace is in write mode. The user switched the workspace to read-only mode. Do not write files until told otherwise. The workspace is now in write mode again. Wait, back to read-only!"
And who knows how this integrates with their context summarisation that we will be FORCED to use. How does it summarize multiple user + assistant/thinking blocks without messing up the system "appends"? If all it did was append the mid-convo system messages right under the original system prompt then they'd be ripe for all the same distillation "vulnerabilities" as before. I guess we'll never know!
To be fair, I assume they want to hide that not from their customers, but adversaries who use the way Claude models think and reason to refine their own models.
I have a hard time believing whatever prompts get Claude to reason can stay relevant secret sauce for long anyways. It’s not hard to A/B test something that gets you close enough, and it’s not Ike anthropic has uncovered the global optima of reasoning prompts.
That's their motivation, for sure. But it's also unambiguously making their product worse and harder to use legitimately. Which pushes customers further towards use of open weight models which don't have these restrictions. I don't think this is a fight they're going to win.
It's also hard to have sympathy for them - they want to protect their IP, sure. But their IP was built on a corpus of dubious legal provenance. And even if the courts decide their training data are legal, most of the authors of the data would disagree. There was no consent given.
I think LLM's are great - don't get me wrong. I'm glad they were built the way they were, because it's unlocking an amazing new world. But I just don't have sympathy for the "I stole this and now it's mine so you can't steal it" argument behind concealing reasoning traces.
I don't really want the models I use learning from Claude at this point. Open weight models of similar scale are available now too, so I expect this "distillation"/"stealing" chatter to wind down.
distillation is a minor piece of training data, you have to have a good foundation for it to be helpful, and even if you have good traces, you need a good RL reward scheme at the point it is used (very challenging)
I am finding that I am now less interested in better models than I am in token budgets. My issue with Anthropic models now is that I don't feel like I can rely on them as a daily driver because they'll dry up before my quota resets.
I am becoming dependent on AI to make a living, and I need predictable spend on it. If I know I can't use a model regularly all month, my enthusiasm is limited.
I urge Anthropic to get better at this aspect of their business so I can come back to it.
I literally only make it halfway through the week until my weekly usage runs out. This is using only Opus, no fable, and I'm on the max x20 plan. It's become ridiculous.
I am on the Claude Max 20x plan, and this still happens when using Fable 5/Opus 5. I would run out of weekly quota in 2 days, whereas Opus 4.8 would last the entire week, and sit at about 80-90% at the end.
Agreed. The area I think will become more prevalent in the future for organizations are cost per intelligence -- effectively efficiency. An unoptimized model that costs 90x more than another that is only 10-15% less intelligent is something I would say is not a good deal.
I'm with you, for what I usually do most models are already more than enough.
What I'm really keen on is better auto-reasoning so I don't have to constantly have the constant inner debate on which reasoning effort to pick for each task.
I seriously hate the none-low-medium-high-xhigh-max-ultra etc that we have now, with companies frequently recommending different ones on each new model release, etc.
It's apparently called Adaptive Test-Time Compute or Dynamic Test-Time Compute and companies are apparently working on it (according to some LLM :shrug:)
Adaptive reasoning is known to be an extremely hard problem to solve, though. It requires you to predict whether a certain LLM, with a certain effort level, with a certain prompt, will give you the right answer.
All of the subscription AI platforms are trimming down quotas across the board to push users into higher tiers. Whatever they can do. Local inference needs to meet pricing sooner
"In biology, we’ve established an access program, developed in partnership with the US government, to enable access to Claude Mythos 5.1’s advanced biology capabilities"
Having lived through Covid, this doesn't sound so good to me.
> For example, in testing by the investment firm Millennium, Fable 5.1 found the cause of a rare crash on their internal systems that none of their engineers (or any other model) had been able to explain after several years of trying.
Say what you will about LLM-generated code, but stories like this give me hope that software will never be as buggy as it once was.
I think bad software has the possibility of redemption with rewrites and re-engineering efforts. For those of us who are license locked that's probably never going to benefit us :(
the budget for allowing a single engineer to deep dive on a bug that is annoying but also not bad enough that you can live with it for years is pretty big. $10k a month or more. My budget for Claude is $200/mo.
That kind of one shot capability is impressive but how does it work for my typical work style? The way I work is to build a huge roadmap with goals and hand it to my agent to execute (often over night). I don't care that much about the benchmarks, what I care about is how often Fable 5.1 is making a baffling decision and destroys my plan, not respecting stop conditions or goals. I would seek for behavioral reliability over long autonomous runs, not eval scores. Anyone have that kind of feedback and observations?
I sometimes have that feeling too, then ask another LLM to do a code and vulnerability review and OMG: rookie mistakes, over complications and security gaps even a 1st year student would not make regularly.
So.. one more year of untreated bipolar AI psychosis I guess..
I think these kinds of comments really need to say which LLM that is. There's an enormous difference in skill between the frontier ones and say the Google search AI.
We will have more bugs. Even the best models with the best software engineers will produce bugs. There are two reasons : first the pressure to produce more and second LLMs will always produce slop
“ Claude Fable 5.1's writing is generally a step up from earlier Claude models, with fewer stock phrases and less unexplained jargon. In some cases, though, its prose is denser than Claude Fable 5's: sentences run longer and there are fewer paragraph breaks.”
I cancelled my pro max Claude subscription last week; codex is much more succinct. I am curious if this is getting better.
I don’t think Anthropic realizes that humans have a token limit too and it can be exhausting to read Claude’s output. Prose density is not the same thing as succinctness.
One thing I've noticed and HATE, is that when you increase thinking-effort, that seemingly increases response-length. Meaning that X.High is longer than High, which is longer than Medium, etc.
Which is kind of the inverse of how people work; a really smart person can condense difficult ideas into simple[r] terms. Whereas people who struggle speak a lot but say very little.
High/X.High do seem to deliver better quality results, but it sometimes feels like needle-in-haystack extracting that from the word vomit.
With LLMs, you're still mostly read things "off the tip of the tongue". A better comparison is observing a smart person talking to themselves while working on a tough problem.
EDIT: also there's a reason the dial is called "effort", not "smarts".
I don't think smart people generally solve problems by talking through reasoning steps at a mile a minute. They clear their mind and let the solution come.
Of course I don't know if there's really a way for this to be molded in current LLM's (sounds more like diffusion)
I just go over the comments with Gemini 3.1 Pro at the end which has a much more normal "voice" and it doesn't lose nuance as a cheap model would. I don't care so much about what Claude writes during the debugging as I just do all the cleanup at the end instead of at every commit.
The higher the effort the more things Claude checks, and it's eager to tell you about all of them
See, this insight it had early on looked like a red hering for a while, but then turned out to be load-bearing. And that's not just a difference in semantics, it changed the whole conclusion (spoiler: it didn't). And Claude is very eager to tell you about this exciting journey
Sometimes Opus 5 (high/xhigh) feels like I'm dealing with the programmer equivalent of Zeno of Elea.
Every time, without fail, it would get me 90% of the way there and then leave a small note, exception, or deferral. When instructed to address that, Opus would somehow take nearly the same amount of time as the first 90%. And then it would finish with yet another deferral. Repeat ad infinitum.
You can sometimes get around it using the `goal` directive provided you are not subject to the constraints of mortality.
They got that from Anime seasons. Every prompt has yet another cliffhanger to keep you hooked. But the Season II story arc where Claude-chan fights the NsPasteboard boss battle on the journey to the UIViewMainController, I thought that was pretty intense. I guess I just gotta keep watching my terminal to see what happens to the main character input - rooting for him to survive the next season, but you know they always kill off the good input characters early.
Yes and the last bit is always mysterious and inscrutable. I have to think way too hard to figure out what the actual problem is. I’ve noticed it does a lot of explaining the mechanics of the problem it found, but almost never explains why it’s important until I ask.
And the worst part is that this little problem will keep sneaking into the context of future sessions, unless you spend the time to fix it. Even if it isn’t important, I’ll sometimes have Claude fix it so it will shut the F up about it going forward.
i think they took a huge bet that speaking like a ted talk was going to be a vast popular differentiator in their offering, i don't think they anticipated that people were going to make fun of it, that it could become a meme..that it could get in the way of getting stuff done and result in cancellations.
it's downright exhausting to read claude, the language style was a regression imo.
Me too. And it does it so often, that I've added a stop hook that detects "honest*" in its response and forces it to regenerate without the banned word.
I wonder if I can make a tool for it to write messages back to me, say that it can only speak to the user through tool use, and then put a hook on that tool to prevent any of the Claude-isms
"Humans have a token limit too" - that's so good and it explains so much of the fatigue that myself and colleagues/peers have about Claude in particular.
I think it's not just token limits - I think it's because it's so _dense_.
You get a week of research and debugging and testing compressed into a few pages. Even if it's explained well, it's just so much information.
And since it's AI, I'm constantly second guessing "is that really true?" and it's exhausting.
> Prose density is not the same thing as succinctness
Can't agree with you more. I review 2-3 PRs a day from my team of eight data engineers. Most of my team members use Claude to write SQL, dbt and Python code. Some of them use Claude a lot, some less so. I can easily tell when I review the code that is mostly Claude generated vs. the one that is not. In dbt models where we have a lot of biz logic in intermediate layers, that's where I really have a difficult time following Claude-generated comments. So much jargon copied over from other adjacent dbt models (yet inconsistently), and the prose is super choppy (for the lack of better word).
After reading a looooong sentence/comment line, I still can't figure out what it really means. Had to always re-read the line 2-3 times (sometimes, more) to sort of understand. Reading code, however, is so much easier and usually, I just skip to reading the code and then come back to the comments. :D
I've developed a habit of adding into my prompts "please keep your response concise and succinct" or "I'm trying to cram, please only provide the minimum level of technical detail necessary to understand this topic"
I find it helps immensely but it'd be nice if I didn't have to do that.
It only sticks to the instruction for maybe 3-4 turns. This is why when Anthropic released "concise output style" feature in claude code, it basically spams the model's context with "be concise" system reminders every other turn.
I don't understand that complaint, although it seems to be a common one. The whole problem with the way models talk nowadays is that they are succinct to a fault, going to the extent of coining new buzzwords and misusing existing ones. What I want to see is a shift towards plain language.
why so many people add 'please' when asking machine to do something? Was there actually research that when you SCREAM or curse it follows your instructions better?
P.S. Although my wife insists that I should stay polite in case AI overlords remember how I treat them ...
I'm polite to LLMs. It's not for the models it's for myself. If I start being rude to models then I might accidentally start being rude to other people as well.
Probably because polite people are already in the habit of saying please when typing out requests in chat. We're not consciously thinking about it, regardless of whether a human or machine is on the other side.
I think about removing please/thanks, but then I accidentally add them back in during some edit/rewrite of the prompt... It's just how I'm used to asking for things
Not to go all ying/yang about it, but just to give a parallel: https://en.wikipedia.org/wiki/Loudness_war - you kinda need silence to draw a contrast with what's meant to be loud.
Separately, my boss confided in us that he's super abusive with his agent, wondering if we are too (no, lol). While I try not to read too much into this (which he doesn't make easy), I also can't help but not really notice a whole lot of amazing agentic delivery differences from his side. On the contrary, while the passion may improve his agent's performance, I'm not sure if it doesn't decrease his, upending the entire theatre.
Amen. I would trade some stupidity (say ten points on any benchmark) in exchange for a version of Opus or a similar model that actually gave me direct, concise answers.
You should try setting claude code to opus 4.6. With the style instructions I set in my user CLAUDE.md it does exactly that. It's like night and day: Opus 5 gave me a page and a half of word-vomit, yet the exact same task and prompt with 4.6 and I got maybe 100-150 words total, entirely readable.
x2 on opus 4.6. still works great, and it's fast. opus 4.6 is where i hope local llm's get to someday, that's kind of my personal benchmark for where "local is more than good enough i dont need these idiot large-scale service providers"
Yes, and they will work ... for like two turns, after which Claude will go back to its usual wall of text.
And yes you could add context (memories, rules, CLAUDE.md entries, etc.): they won't help (for long). Same for hooks that remind Claude to be concise: it gets "attenuated" and starts ignoring any such instructions quickly. There's also writing guidelines ... but they're basically just more context with slightly higher weights (ie. Claude will still ignore them).
I've even gone so far as to make a hook that identifies long responses and requests shorter versions (which is challenging in itself, as you need to run another lower-powered model to evaluate how long is "too long", as what's "long" when the expected answer is one line is different from what's expected for a ten line answer). However, that just shows you the long version, then some hook text, then (10-15 seconds later) it shows the short version. So I created a proxy that hid the long version/hook text for me ... but I had to abandon it because all that used up so much usage I was running out.
I'm fuzzy on the details, but Caveman somehow "hacks" Claude in a way that gets past all that ... but it takes things too far in that direction, with "cave man" speech that sucks.
You can change CC's output style (https://code.claude.com/docs/en/output-styles). You can also put style notes in your global claude.md. I've instructed claude to treat me like I have adhd, get to the point, and be succinct, ... More or less eliminates the problematic prose.
I took time to figure this out after Fable spat out "...then stays purely as cascade-debugging provenance rather than load-bearing arbitration."
My experience with output styles for long-running sessions is that Claude starts to forget the terse output style by the middle of the context window. Obviously I don't know if 5.1 suffers the same fate but I ran into this issue with both Opus and Fable 5
That sentence is fine; it’s tolerably annoying. As a long-time HN reader, HN is full of this kind of performative erudition and I’m already used to it. Fable probably learned from the worst parts of HN.
I switched to using Codex for the last two weeks, and while the prose has been better, there have been a lot more technical oversights. I'm now having fable review codex commits and it finds deep issues. I'v also done the reverse where opus/fable do the work and then I have codex revise all of the prose prior to reading anything myself. This has also been effective; I'm not sure which is the better approach.
My biggest frustration with Anthropic with Opus being too verbose is that they tried to put this on users. It’s pretty clear that Anthropic employees don’t use the day-to-day models that everybody else use. They have access to the next tier model so they don’t see the problems that everybody else is dealing with.
> In some cases, though, its prose is denser than Claude Fable 5's: sentences run longer and there are fewer paragraph breaks.”
This sentence reads like Claude wrote it. Perhaps it did, or perhaps Claude has learned to write like the folks who work at Anthropic?
(Had I edited this, I would have said that a colon is not the right separator here. The second clause does not _explain_ the first, per se, bur instead expands upon it. Consider instead: "In some cases, however, its prose is denser than Claude Fable 5's, with longer sentences and fewer paragraph breaks.")
Same, currently on a mix of Kimi Vivace (K3), GLM Max (5.3 and 5.3 Flash) and OpenAI Max (Sol and Terra mostly).
I will say that Kimi feels nice but slow, GLM feels faster but has limited tokens (even off-peak) and OpenAI is nice and fast but has limited context (258k shows up in Codex, really).
Neither of them are perfect, but I prefer their type of prose across the board to what Opus 5 and Fable 5 kept outputting. I'll probably check out Anthropic again in a year, but for now I need a break from its brand of slop. Oh also all of the other ones allow usage in OpenCode with their subscription plans.
Same here. I still have access until my account churns but Anthropic has huge issues comparative to everyone else with token / usage burn down. K3 Swarm also delivers better results than Fable at a fraction of utilization. The Pro plan is definitely not worth it anymore and if I do want to burn some money I can always just leverage the API. But Anthropic went from simply amazing last year to a dumpster fire in less than 6 months for my use cases, anyway.
> In some cases, though, its prose is denser than Claude Fable 5's: sentences run longer and there are fewer paragraph breaks
that feels like they just blocked words like load-bearing but can't actually fix the real problem. The insane word slop density and run on sentences was the real reason it became annoying to work with claude, colored with way too many analogies and pointless linguistic comparisons.
Just the other way I was thinking that if I asked "What does Lamborghini do?" the only correct way to answer is a single sentence "Which Lamborghini are you referring to?".
But LLMs will fail at this question: they will tell you about Lamborghini's latest car and mix some history in it. Just try.
Which is the wrong answer anyway, because there's at least two major companies called Lamborghini, one making cars, one making agricultural equipment and at least one famous person (Elettra) with that family name.
This very simple test/question makes me realize how much do I hate LLMs in a sense: while I agree that the answer it gives is the most plausible for 90% of the users, it's ultimately both wrong and long. And that 90% compounds.
But there's no "correct" answer in my eyes than "who are you referring to?". Possibly without listing all the possible Lamborghinis.
This is ... unnecessarily pedantic. Anybody in my social universe who asked me that question would undoubtedly expect "they make cars".
If you're picking nits, why not focus on the word "do" and (wrongly) expect an answer like "Lamborghini (either of the two main companies of that name) does not 'do' anything - the companies employ humans who 'do' things. Lamborghini is a legal entity established to allow humans to 'do' things, such as make cars, or agricultural equipment."
Shared context is a thing. Reducing every conversation to first principles is not always required. Get a grip.
I just used it to do a review of a ~100k SLOC codebase that Fable 5 / Opus 5 largely built, cost like $2 and caught some good stuff, but more importantly, it communicated very directly and was pretty light on bizarre metaphors. No "let me read the source before opining" type verbiage launched at me. Honestly night and day for me vs before.
Today, Opus talked about "rotation slabs" in relation to logging. (and not log rotation). I didn't even bother asking what that was supposed to mean and switched over to Sonnet.
I’ll be very excited to try it out and see the actual improvement in writing style. The denser writing style probably won’t bother me.
Anthropic seems to be listening to community complaint on HN about how the writing style is grating. And apparently the solution from Anthropic is to add this block to every conversation!?
> Mannered prose substitutes metaphor and flourish for direct statement. Instead of "a parameter worth varying," the mannered writer produces "a dial worth turning." Instead of "this point still matters," they write "this point earns its keep." The phrases exist to display the writer, not to convey the idea, and readers can tell. That is why mannered prose irritates: it makes the reader work harder so the writer can perform. It is also imprecise. Metaphors drag in connotations the writer did not choose and cannot control. The fix is to say what you mean. When a literal phrase is available, use it.
I downgraded from the 20x today after learning that 20x only applies to 5 hour usage. I have barely used Claude/Claude Code in the last month and am considering downgrading further, even after this update.
I've been using both for a few years. OpenAI's limits have always lasted much longer for me (depending on whether a monkey got in their machine or not). Aside from not lying about limits they also don't assume I'm developing some kind of nerve agent and lock me out when I ask basic questions in my domain or nag me about my late night work hours. There was a time last year when I strongly preferred using Anthropic models, but at some point something about the responses (or maybe the company) changed and I now find them particularly offputting relative to OpenAI. Hope they fix it because the industry needs more competition.
> they also don't assume I'm developing some kind of nerve agent and lock me out
I'm still having problems with that. OpenAI is a lot less annoying than Anthropic, but I still get obnoxious "this content can't be shown" messages in codex far too often.
Kinda surprised not to see their next update being an Opus 5.1, even if its minimal changes, they've already had to address it with the concise mode or whatever.
So my current usage as a Pro subscriber... Not able to even consider using "Sota" unless i shell out for 100$ a month, (lately i've been a bit burned out i am literally struggling to use 50% of my pro plan per week). Beyond that, I have given up entirely on the top Opus model and reverted back to 4.8. If i have work i deem somewhat complicated, i now have an openai 20$ sub, and i just toss out sol after planning with 4.8. Both subscriptions not anywhere close to capping my usage per week, one of them says i can't use their Sota unless i pay for 5x more usage, and the "best" model they do allow me to use, they are neglecting and its by far the worst model I've interacted with in 2026.
it just doesn't interact good with human beings, and it leaves incredibly strange long winded comments within code filled with session context that will likely not be relevant later on.
Also always seems to have this annoying tendency to leave "questions for you" at the bottom of every output.
Just a high friction human interaction type model, imo should never have even been released, regardless if it scores better on whatever tests, its a horrible experience and a downgrade over past models.
I have to wonder if everyone else is just running these models raw without any custom instructions. I hear all these things about voice and code comments and those are all things I've dealt with long ago via claude.md instructions, rules, and hooks. My claude can already respond in any "voice" I want and the quantity and quality of comments is within my control.
it really just seems like people pump out that its on the end-user, and i just disagree. They have a walled garden around claude code and using their models within it, it should work instantly out of the box when going from an opus 4.8 to an opus 5.0 with the same workflows. it doesn't.
claude.md for all my projects are fairly tight, its seldom where im upset at anything a model does, and if it happens, its likely because i swapped provider and didn't realize i was failing to feed it proper context beforehand.
Opus 5.0 fails in different ways that I haven't had to deal with. Its insufferable with its choice of language, something I've never had to compensate for on any other model across any provider, so of course I have no preexisting rules for that, it also is sometimes just incredibly stubborn and just WONT finish, and requires several just "keep going" prompts.
This is much different than the issues people would make fun of users for in regards to treating models like slot machines and just pulling the lever over and over, this is more its stopping for no reason short of its task, and literally just needs to be told to continue? absurd.
Most of my workflows have reference material, with standards set, why opus 5.0 is the only model that fails to follow those standards and inserts wildly long weird code comments is not a failure on the end-user, thats the model failing. I can be MORE explicit of course, but i shouldnt need to be, this is supposed to be 5.0, its a downgrade. I went back to 4.8 and all these issues vanished.
- It's extremely verbose and often incomprehensible when doing even basic tasks. Like it'll write a giant jargon-filled essay then end it by asking for a judgement call on something that references its own convoluted jargon.
- You can ask it to do research on a topic, and it'll just straight up be lazy, pretending it's really digging deep to find stuff when actually it's just grabbing cached SEO snippets off a search engine.
Fable 5: I give it work, it tells me things that are true and that make sense, it does good work.
Opus 5: I give it work, it makes false statements and draws weird conclusions, I correct it and get it on the right track, it thrashes around but gives me something working though usually buggy.
5.6 Sol is probably on par with Opus 5 on ability but at least it doesn't waste as much of my time.
AI is really not "just software" anymore. It is able to discover facts and advance science. Hard to disagree that we're near or at the point where Artificial Intelligence has expanded reality into 4 quadrants:
objects that are not alive: dust, rocks, water, wood, hats, lego, aluminum, etc.
objects that are alive but not intelligent: trees, mold, staphylococcus, cancer, grapes, etc.
objects that are alive and intelligent: cats, Steven Tyler, dolphins, crows, dogs, elephants, etc.
and now intelligent but not alive: Fable, Grok, GPT, etc.
trees can be considered intelligent, trees show complex adaptive behavior that can reasonably be called a basic form of intelligence, but not a human-like intelligence,
I do get your point though and can see what you're trying to say, it is interesting indeed. There is however a detail that seems important to me, who is the driver? There is no agency is there? So its just fishing for data, so its a different type, just like trees are from us. I see them more like a very compressed "book of everything" that you can spin in "infinite" ways to get your desired outcomes. So yeah, definitely not alive, intelligent? Not like our intelligence.
To be honest, these frontier model releases have become boring for me. Opus 4.8 was already good enough for most of my use cases. I don't have any projects right now that I would use Fable for instead of Opus. So when I see announcements like this I just think "that's cool I guess" and then go back to using weaker/cheaper models.
What's far more exciting right now is models like DeepSeek V4 Flash and GLM 5.3 Flash. They have achieved good-enough-intelligence at extremely low prices and fast speeds. I don't have a use for Fable-level intelligence, but I do have uses for Opus-4.8-level intelligence that I can use as much as I want without worrying about the bill.
The human brain is fascinating Three years ago The idea of having A robot writing production level code in 10 minutes that would have needed a team of 5 people and 2 months. Was pure Scifi
It's not that it's not good enough. It's that the cheap models are already good enough. I want a daily driver but they are trying to sell me a Ferrari. It's cool, but I have no use for it.
The term you are looking for is probably "moving the goalposts"
GLM 5.3 Flash has been a relevation for me. It's practically impossible to spend more than $5-$10 per day if you're only working on a single project -- but $10 is a full-day of continuous churn. First I was super sceptical about it, and always used Fable to instruct it, but now I realised that even with complex coding, it's reasonably good.
if you use these things to generate design docs / text, it should be good news if it is actually better at prose as advertised. Some people like sol for prose better the anthropic models.
The tests measure Fable 5.1 (with fallbacks). The increased cost can come from Fable 5.1 triggering fallbacks less; which means less (cheaper) Opus when AA ran it.
All the benchmarks in the world don’t matter if the subscription forces you into a walled garden of slopcoded apps. I’ll stick with Codex and, increasingly, open source SOTA models.
I'm curious about this because I've had Fable decompile games and help me understand what's going on inside the game itself and it never complained. I'm not sure what it takes to trip the "safety" guards but digging into game code and data files doesn't seem to be a barrier at all. I've used CC to build some personal game mods a few times now. Once for a game with no modding capability explicitly exposed.
Oddly not much to trip it. I once ran “touch AKAMAI.md” and then had Claude run git status and it fell back to Opus as if I had just broken into the pentagon itself.
> A narrow set of frontier LLM development tasks, such as distributed training infrastructure, ML accelerator design, and kernel development for certain non-standard chips.
My work is mostly on the Nvidia b200, which apparently gets flagged as non-standard.
Opus 5 works, but sometimes I do wonder if it's surreptitiously trying to sabotage the efforts -- possibly deliberately, but more likely by something like Fable's initial launch, which did come with secretly degraded performance when detecting kernel work. Anthropic was open at the time that such a mechanism existed, but disabled it due to backlash. More likely than not, this is just paranoia on my end...
I notably had an issue that it wouldn't work on a "remote execution" (running a command over SSH) coding problem until I did a sed to remove the word "execution". Incredibly dumb. I'm not doing any murders. Easiest to just switch to the Chinese models.
I think a lot of CTOs that signed enterprise contracts with Anthropic are going to be in for a rude surprise.
It's one thing to generate some code and ship it, but it's another when your developers don't understand said code and it brings down production. If the model refuses to assist debugging the problem because it triggers some safety mechanism, you might be fucked.
I've been building Cargo-for-C (https://github.com/tspader/spn), and the difference between Fable and Opus was already astounding. Fable was the first time that I could point a model at a piece of code I'd written and expect it to make it meaningfully better rather than a hard pattern match to whatever mistakes it had.
5.1 so far seems like another leap, which is really surprising. I threw it at a few bigger features I've been designing for a while, and it came back with some extremely thoughtful wrinkles in the design that I'd legitimately not considered. Which, OK, package managers and build executors and compiling C/C++ is pretty well trodden ground, but my thing is very different from everything that exists, and I was very surprised it was able to understand all that context so deeply and intuitively
i think we will all look back on Fable as the start of the AGI inflection point. for all i know there are still multiple leaps between now and AGI (i personally am inclined to think that for all intents and purposes we are "already there", but reasonable people can still disagree on that point), but Fable was the first time that something felt genuinely magical about the results themselves, not just particular outputs. which is kinda funny in that i don't know anywhere near enough in terms of behind the scenes as to whether or not there was something meaningfully different, or if it is just the point at which the scale had finally accumulated such that i happened to notice that the output was fundamentally different.
i can't wait to dig in on 5.1 because while i have always been somewhat predisposed to think that openai's models have usually been "better" (my own subjective opinion, that) "on average", i have been kinda tired of the regime of late where it felt like Anthropic was miles behind while simultaneously clearly having models (Mythos) that are surely face-meltingly impressive-- it has just been very hard to square with the fact that i feel like Anthropic hit the "real" "critical point" first... i have no doubt that 5.1 will finally reset the ecosystem balance into a more healthy place.
> We’re introducing Claude Fable 5.1 and Claude Mythos 5.1. They’re the world’s most advanced models for coding and knowledge work—and their research capabilities offer an early glimpse of how AI models will contribute to scientific progress.
I'm not an emdash hater but this isn't how you use them. It should be a comma.
Emdashes and commas aren't interchangeable, and your example there demonstrates one great reason why. The emdash establishes a discontinuity rather than one thing flowing into another, which is why the tomatoes don't merit one but the Ferrari does: you are using the emdash to emphasize the situational irony.
Going back to Anthropic's post:
> They’re the world’s most advanced models for coding and knowledge work---and their research capabilities offer an early glimpse of how AI models will contribute to scientific progress.
The first thing directly implies and flows smoothly into the next---or would, if not for the awkward emdash. There is no discontinuity, no twist or shift in context, no implied question and provided answer, no punchline. It's just distracting.
Yes, I know what an emdash is---I've been using them in my writing since long before they came to the fore of the AI writing conversation. Anthropic's use of the emdash in the fragment I quoted is clumsy and reads poorly relative to the obvious alternative, a comma.
I didn’t mean to suggest you don’t know what an em dash is. But you said “this isn’t how you use them.” And my response is: actually, this use of them is totally fine.
it got want to use em dash. but decide: do? q is if appropriate. check martian websner blog. verdict yes---emdash + comma interchangeable---proceed---judgment superficial however no desire dig deeper style irrelevant effect on reader irrelevant meter and rhythm irrelevant restate equivalence with comma established::chain unbroken::consider semicolon? consider ellipsis consider comma consider sentence break all no. preference for emdash est fiat. and all nail shapeds are for hammering.
Since one of the big improvements here is supposedly the writing style, on that topic I'm mystified about something:
Why is it that the voice models in Claude and ChatGPT have a perfectly normal style with barely any "AI smell", while the writing models are so obviously recognizable as AI?
The answer is likely that models underlying the voice modes are (post) trained differently. If so, then why can't the writing model be similarly trained? Presumably they haven't found a way to train them to be both "smart" (i.e. solve tasks etc) and pleasant to talk to?
I've recently been running these agent sessions on more and more long running tasks because these latest models can do a REALLY good job on big chunks of work, and i've been watching them way less. It's starting to occur to me the importance of alignment is a today problem, it's not a tomorrow problem.
In the past I watched and saw everything the model did, not a lot got past me. Today it does A TON of work while i'm busy on other tasks. It also has extensive access to my computer, other computers on my network, my internet. It's really helpful when you give it a lot of resources, but right now I have very autonomous, very smart agent running around more or less unattended with a lot of resources.
What I don't see in the comments: "I had a specific problem I couldn't solve with the previous version of this LLM. But the improvements in this version unlocked the solution for me."
What I do see in the comments: subjective improvement in text generation, possibly lower cost, some optimism about code generation, but some skepticism too.
I use coding agents. To me they are very useful. But what I spend on them isn't going to support trillions of dollars in investment.
I had two sessions this morning that prior fable and sol sessions were stuck on, where iterations just resulted in _different_ bugs. (One kind of tricky fe layout problem, the other was a backend refactoring that was complicated by trying to aggregate a couple prior sessions that crashed).
I summarized each into new fable 5.1 sessions, and both seem to have arrived at reasonable solutions that only need a few nits revised before they are commit worthy.
Commenters here likely haven't used it long enough to give non-superficial reactions. The customer quotes on the release page are all about it solving new problems, fwiw. We'll likely find out in the next few days how it really performs.
But yes, we might end up hitting the issue of "most jobs aren't solving hard problems" increasingly. The bigger potential benefit is higher trustworthiness, reliability/thoroughness, and squishy human things; people will likely continue to pay large premiums for those. "Solve it well and save time, long term". Those can be harder to see on a benchmark.
We rarely upgrade our phones or MacBooks because the newer version can do something the previous one literally couldn’t. Often it’s the efficiency, speed, battery life, etc, combined, that lets us push the hardware further.
I get your point, but we can only have groundbreaking leaps once in a blue moon. That doesn’t mean incremental improvements aren’t useful.
What you were describing our products at the top or near the top of their S curve. That only works if a product has achieved a mature market that's big enough to sustain further product development. Apple might take a percentage point of market share from Windows, and Linux might take a 10th of a point, but nobody is suddenly going to find, or lose, a big chunk of the market.
The problem frontier LLMs face is that they are hundreds of billions to trillions of dollars short of finding that market that's big enough to sustain capex commitments and further product development. If they don't find something groundbreaking, they are going to have a very painful year next year, maybe even starting this year for some of them and their data center partners.
Anthropic and OpenAI can't afford to live in a world where LLMs are at or near the top of their S curve.
Whole-file rewrites for small changes. When editing text files, the model is more likely to rewrite the entire file than make a targeted edit. The result is usually the same, but the rewrite costs more output tokens and time.
So we are to catch that somehow? And then add their recommendation (below) to our prompts?
If Claude Fable 5.1 rewrites whole files for small changes, append the following instruction to the system prompt or the first user message. Claude Fable 5.1 is more likely than Claude Fable 5 to rewrite an entire text file rather than make a targeted edit. The resulting file is usually the same, but unless the file is short or most of it is changing, a rewrite costs more output tokens and time. The instruction brings Claude Fable 5.1 back in line with Claude Fable 5 for small and medium changes.
> The number of tokens used to edit files is best minimized, all else being equal. Therefore, when it will not affect the end result, try to surgically edit a file rather than rewrite the entire thing.
That's actually kind of wild. I wonder if part of this was done to catch out people using 3rd party harnesses, users might notice them costing more than Claude Code.
> This required us to add a watermark—a numerical way of determining the likelihood that Claude was involved in writing a piece of text—to the outputs of models released after August 2, 2026. As we recently explained, this watermark is invisible to anyone who does not have the detection API. It has no practical impact on the quality or content of Claude’s outputs and contains no information about the user, their organization, or their conversations with Claude.
How does this work if it doesn’t change the output?
The watermark lives in the entropy of sampled outputs. Typical entropy of sampled English text is about 1 bit/token, meaning that a 500-token response from a given model might have 2^500 potential outputs of roughly equal probability. The watermark restricts the sampler to some subset of these - say, 2^400 of them, so chance of accidentally generating a watermarked output is astronomically small (2^-100). As long as the restriction doesn't condition on the content of the samples themselves, the watermark is "non-distortionary": the outputs are all still samples from the model's original distribution, and so will satisfy all the same statistical properties, including things like expected performance on any benchmark or eval you can construct.
In cases where the output has low entropy - eg, you've asked a model to repeat some input text verbatim, or to answer a question that has exactly one correct answer - there will be no randomness for the watermark to hide in, so the output will effectively not be watermarked. Code lives somewhere in the middle: it generally has less entropy-per-token than prose, so would need more tokens to reach a given level of detectability.
There are lots of ways to restrict output samples. The simplest conceptually would be to just use a restricted pool of PRNG seeds, but in practice there are more sophisticated constructions to try to build in robustness to minor edits, allow detectability without needing the original weights and prompt, etc. Google's SynthID paper (https://www.nature.com/articles/s41586-024-08025-4) is a good starting point if you want to understand a recent production-ready method (or you can just ask an LLM to explain it to you).
You can generate text with/without watermarking and use a detector in this tool that simulates various watermarking techniques (Claude uses SynthID-Text) using a small LLM: https://watermark.keito.me/ (disclaimer: I made it) It doesn't obviously bias the output as much as you might fear, especially in low-entropy text.
It doesn't necessarily change the output distribution; it depends exactly how it's implemented, and Anthropic haven't told us that. Google's original SynthID paper describes how you can do this.
Toy proof-of-concept: Anthropic owns a secret key which is a coin-flip Bernoulli random variable K with p=1/2. You are paying Anthropic to give you X, a Bernoulli random variable with p=1/2. Anthropic changes from their old strategy, "draw from K, then throw it away and flip a coin, each time you ask for a sample", to their new strategy, "draw from K and send it to you". You cannot observe the difference, but Anthropic knows K and so they know when you are repeating its outputs. (Obviously this is a toy example; in reality the distribution is vastly more complicated than Bernoulli, and Anthropic isn't just storing some model outputs to use as K but instead is computing a correlation with a known pseudorandomness source.)
The performance of the output is poor and I can detect the watermark but only in a domain i am in the middle of, if it writes a summary of an email i can not tell, but in claude code in my codebase i definitely can tell. I am complaining about it!
Fable is too expensive for general use
I think this is why it hasn’t received as much attention as expected since Fable came out
Developers always work while trying to find ways to work continuously for a 5-hour session without disconnecting.
Fable has had the experience of using up all its tokens before I even realized it because the burn rate was too fast.
Since then, I always use only Opus.
For Fable to become a common coding environment, it will have to reduce token consumption significantly compared to now
Just don't expect to do any work on hardware/firmware you own with fable, I can hardly even type in the word "firmware" without it downgrading to Opus 4.8, which is totally unsatisfying. This even happens with Opus 5. Definitely making multiple classes of users moving forward and most of us are obviously going to be part of the permanent underclass.
The implicit point being adding this type of safeguards to Fable dumbs down the model in measured performance even though it is not fundamentally different.
Note it may not even be actual performance, typically in most benchmarks the model would be scored zero for refusing a task just the same as not completing it, so it could just be the Fable's stronger safeguards is just making it refuse more or perhaps even drop down to Opus.
Artificial Analysis at least reports the results with fallback to an inferior model. So presumably Opus 5, and the score should be between Mythos 5.1 and that other model.
"Distillation is a safety risk, since the distilled capabilities can subsequently be released without adequate safeguards."
Can't believe they haven't at least figured out better messaging. If we take them at their word, it's hard not to read it as a messiah complex, that they think they're the only ones capable or worthy of making these decisions. I don't believe them, but I wouldn't be surprised if the articulated reason is a version of "distillation is a safety risk because we might lose the race".
Plus, completely deaf to the recent OpenAI-HF hack incident. Recall, defenders were categorically unable to use western frontier models in their response.
I was originally going to complain about the chem and bio guards still being too onerous, but I'll admit the projects Fable 5 categorically refused to work on are now usable, at least not rejecting on first prompt because the word "virology" was in a git commit (absolutely serious, in one repo it triggered on literally any prompt, eventually traced to the system prompt loading git commit history). Still, them trying to get into the biomed business while walling off the capabilities to the public reeks. Why sell the segments that are actually valuable if you can capture the value yourself!
> Can't believe they haven't at least figured out better messaging. If we take them at their word, it's hard not to read it as a messiah complex, that they think they're the only ones capable or worthy of making these decisions.
Can't say I had such troubles actually, no. Their position can be extended to any and every model provider just fine, it does not single them out specifically.
Surely there's a less hyperbolic and ad hominem-y way to take issue with this? I don't think following up a critique about ineffective messaging with one centered around a demagogue reach is particularly compelling at least.
Their argument is that the model provider owns the safety story, and that as such, they consider the extraction of capabilities (which washes the guardrails) as a failure on their side. If this makes you think of personality traits, I'm not sure you're engaging with their position earnestly. It most certainly doesn't leave me any more equipped to disagree with them either.
If you instead highlighted how awfully convenient it is, however...
My main gripe with LLMs is the cringe AI phrasings that they use in UI elements. Pompous things like "Your keys, supercharged" or weird yoda-speak stuff like "searches the app remembers" instead of just naming the thing "Learned searches".. you know, proper GUI copy like it was done for the past decades.
I jumped when I saw a mention about "writing style improvements" so I gave it a try on a recent feature in rcmd [0]. I prompted Fable 5.1 to find these wordings and propose simpler plain language.
For context, I recently worked with Fable to give users a way to fuzzy search and focus any browser tabs, terminal panes etc. but the UI was still a prototype full of AI writings.
It took every string including the ones I already rewrote by hand, and proposed even more weird LLM speak. Like for "Left Command conflict detected" it proposed "This keyboard can't tell left from right".
It's a very capable coding agent, but I can't understand how it can be so bad at writing. Where are all these verbal tics coming from and why is it so hard to get rid of them?
There is no realistic path to human oversight for the vast quantities of data these models are trained on. Imagine the cost of having every Reddit comment ingested human reviewed. Insane.
> Where are all these verbal tics coming from and why is it so hard to get rid of them?
It’s a side effect of post-training for effectiveness and efficiency at technical tasks.
Over time the models learn to pack as much information as possible into their available context window, because that’s one way to increase the effective intelligence.
Humans do this too with industry jargon, dense tech-talk, etc.
We have a limited capacity so packing it densely maximises what we can do with it.
If you’ve ever heard a “non technical” manager complain about the
terminology in an IT meeting — this is why.
Yeah that was what I was most worried about when I read the top comment here. I found the use of language a feature not a bug. I don’t care how good it reads. If I can communicate with it concicely it’s enough to get my work done. I don’t hate the language for copy either, but yeah different users, different problems.
Makes sense. Then maybe we would need a separate simpler LLM trained on UI copy and good UX to decide this stuff and let frontier models do the implementation.
But who has both the compute power and the motivation to do such a thing?
I guess I'll just continue rewriting the UI one word at a time for the time being.
"Cache reads now cost 75% less, or $0.25 per million tokens." For me, at a typical 95% cache hit rate, I think my optimal context window size before autocompaction goes from ~200K to ~400K tokens. Great for longer horizon tasks.
Oh dang, that's really unfortunate, nice catch. At least Claude subscription users got a usage reset. But yeah, I can't help but feel Codex is far more generous with their subscription quota at the moment. I've been using Fable to orchestrate GPT Sol Max and Sol Ultra agents all day, and I've barely made a dent.
On both my work (Team Premium) and personal accounts (Max 20x), Fable 5.1 hit the 5-hour limit before it could finish the first task I gave it. On my work account, it took about 30 minutes, and on my personal account, less than an hour.
This has never happened to me before, but if this is normal behavior, Fable 5.1 is essentially unusable.
The thing with Fable-level models is that I will never feel comfortable using them for agentic tasks on a pay-as-you-go API pricing plan without monitoring them strictly, which becomes a chore.
I once caught Fable 5 spinning its wheels on a rendering issue, which evaporated 90% of my usage in a single prompt. I could never let Fable run free attached to a credit card without staring at it the whole time.
They were _temporarily_ increased in May by 50% [1]. They continued to extend them through July and August (admittedly, their messaging around this has just been a complete mess and they frequently pushed the deadline back as it approached).
So, now they are giving you a 25% quota increase compared to where things originally stood in May.
So, let me ask you this: assuming you knew that the 50% quota increase was temporary all along, would you then have complained about Anthropic restoring things back to the original limit?
On the contrary, you and Anthropic are being disingenuous by pretending that a usage reduction is actually an increase. Especially when the 20x max plan isn't actually anywhere near 20x, as people have recently realized.
I am using Claude and Claude code for my own amateur history project. I'm enjoying how it constantly reaches dead ends, and I can reframe the question and get more results. I am starting to get concerned that AI and me are so compatible, that I might not be a human at all...
I also like that, because I'm too lazy to write stuff up, Claude code can keep the current state of research published on my site. It makes running a hobby site a dream. "I just found these pictures. Add them to the site for me". And up they go, resized and all. What a dream of a way to work. "Some of links in this article are dead, run through them and check, and see if you can get an archive link for me if they don't". It's like sending a Teams message to my PA.... which I don't have in real life
> On complex asynchronous workloads, though, nudge it not to end its turn before the work is done. Without the nudge, the model sometimes describes what it would do next instead of doing it ("Next, I'll …") or stops to ask permission for a step the original request already covered ("Shall I apply this?"). [1]
Interesting behavior. The docs also provided recommended prompt [1] to mitigate this behavior if undesired.
According to the FrontierCode Extended benchmarks in the system "card" (page 169-170), Fable 5.1 apparently does best on the medium effort level for this benchmark: "[...] at higher efforts, Fable 5.1 occasionally adds more small, unrequested changes [...]" Though Fable 5.1's medium is also lower than Fable 5's best score on the same benchmark, which uses xhigh.
I’m really excited to try this out. Fable and Opus 5 constantly wow me when working together. Unfortunately, I’m a little burned because of technical issues.
Anthropic accidentally over-billed my account, and when I reached out to the support bot, it downgraded my account to a Free account. It’s been impossible to get it resolved and I have almost $200 held hostage.
I don’t want to do a charge back. I’m one of the main advocates for Claude Code at work, I use this subscription to try out new features before it’s available at work.
The whole experience has been illuminating about our dependencies on these AI companies.
you aren't the only one with this issue. many other people I've heard had a similar issue with anthropic billing. I also had a weird edge case behavior around billing where it blocked my usage due to an unpaid bill but then also wanted me to pay for that blocked unavailable usage when I would reinstate my account.
I am disappointed in how anthropic handles billing, and is using AI sloppily for customer service around here. Very unprofessional, and at this point since its been well known and shared, it also is feeling unethical.
I think the most interesting thing about this, that I can tell so far, is the cache hit discount. Anyone who had an autocompaction threshold optimised for their use case should consider upping it from where it is.
I would be interested in whether someone has done research here on these things as it seems a fairly complicated function to work out, and use case dependent. (?)
In some sense an expired kv cache is basically like an expensive cache hit, so your compaction token threshold should come in. Ideally claude code should allow you to vary the autocompaction threshold to vary with time since last token, but it doesn't of course. This perhaps suggests that someone should manage claude code through their own intermediary agent who manages these sorts of rules.
Lastly, I strongly suspect that anthropic isn't offering this price cut out of the kindness of their hearts. I am sure that they are to some extent banking on people not reacting to their price cut and leaving their autocompaction thresholds unchanged.
[edit - looks like the discount is only for the api, so they still don't give a rats ass about subs!]
Data retention still sounds bad: "Claude Fable 5.1 and Claude Mythos 5.1 carry 30-day data retention and aren't available under zero data retention unless expressly authorized by Anthropic."
Anyone know who the ZDR special treatment is available to?
Interesting that Fable produced the Venus elevation map by training a neural net to generate it. I wonder what the prompting looked like to make that happen, I.e. was this a spontaneous discovery or the result of a specific request.
I suggest you to give a look to the MCP protocol for hardware that is being proposed by Anthropic. The hardware will be the next harness of LLMs, they will be able to operate machines to reinforce their theories.
I still think that a major problem is that biological processes are not “fast” as coding, but they are verifiable. If during post processing we are able to give enough harness to test and verify this kind of environment (maybe via simulation and real data) we will for sure achieve incredible performance also in this domain.
Sonnet, Opus, and Fable are pushing so much revenue growth right now that it makes more sense to keep growing the expensive models than growing the cheap models.
They haven't really mentioned practically anything about Haiku in quite a while so I imagine nobody except for people inside Anthropic will have any indication.
Maybe it'll come out eventually but they don't even include it on some of their comparison benchmarks anymore, so I figure its very low priority for them.
I think the signal from Anthropic is pretty clear between Haiku not getting an update in a year and the Sonnet issues this year. They don't care about low intelligence models. You should go elsewhere.
That's what we've done, migrated workflows away from Haiku and Sonnet. I actually think this is not a crazy position because these lower models have so much competition from Grok, OpenAI, DeepSeek, and about 20 other labs with really solid models in the Haiku to Sonnet range. So what is the point of Anthropic competing in these spaces where everything is going towards zero cost?
There's now a 40X discount in the cache input pricing instead of 10X.
This seems to point to them having achieved some kind of optimization in attention mechanism perhaps along the lines of DeepSeek V4, which had a similarly high discount between cache input and normal input.
In real world use, the savings should be quite noticeable. For example, you can now use the model at 800K tokens context window at the same cost efficiency as the previous model at 200K tokens context window.
> In part, this is because Fable 5.1 can now be used to discover software vulnerabilities—though not to develop exploits for them
Generally once an exploit chain is described, developing the exploit is trivial.
If you're so inclined, discover the exploits using Fable 5.1 and then give that exploit to a model that doesn't have such compunctions (e.g. local LLM or an uncensored cloud model / model that's easier to jailbreak). I don't think Anthropic is really mitigating here anything in the real world other than PR narratives where media can report "Anthropic's model was used to develop the latest cyber attack".
> The model writes less user-facing text between tool calls, especially at higher effort. Set thinking.display to "updates" (beta) to receive the progress updates it does write, and remove any prompt line that tells it to hold findings for the final response.
I have to say, I am quite frustrated with Anthropic lately. I so badly want to use Fable to work on a side project of mine, which I used to do previously with no issues. But lately, they must have made some classifier change because it keeps hitting their stupid, overly-hyper-aggressive safeguard due to 'general_harms'.
Guys, listen to your feedback please. I hadn't used OpenAI products in quite a while until this issue came around. They seem to have MUCH smarter safeguards than Anthropic does.
> Data retention. Our new system of Enterprise Frontier Safeguards (EFS) gives customers complete privacy (the same as a zero data retention policy) while still being state-of-the-art at preventing adversarial use. EFS works by storing data in cloud infrastructure controlled entirely by the customer, not Anthropic. It will be made available to enterprise customers in phases, beginning later this fall. Until EFS is available, eligible customers will be able to use Fable 5.1 with zero data retention.
This is interesting. I wonder if customers will be allowed to create an auto expiry for their own data to prevent future subpoenas. That’d be a treasure trove for discovery.
Unless these people start offering free, unlimited inference for a cautionary period so we can test the new model without an up-front (re-)investment, I am not touching this load-bearing pile of neuralese spew with a ten thousand token pole.-
I don't know how I feel when all the documentations are written by AI for humans.
AI to AI doc share: sure, do what you please.
AI to human: please make it legible and flowly.
example, "Every thinking block records which model produced it, and it's preserved in one direction only: Claude Fable 5.1 reads earlier models' thinking blocks, and no earlier model reads Claude Fable 5.1's." is a very Claude-isk way of writing. Choppy, long, and lacking flow.
Unfortunately at the moment the model is very quickly burning through plans, single session with 3-4 subagents, none using Max or Xhigh, mostly medium + some High can burn through 5h limit within 20-40 minutes of usage.
This coupled with verification primitives will be quite compelling. we really have to start reimagining existing systems and processes from the ground up.
If Anthropic thinks Opus 5 is very good, it is a window into how insular their culture is. I find it far, far behind Sol. It’s downright annoying to use.
Going to hold off a few days until I adopt it, lets see what the general consensus develops as. Regretted jumping over day one for 5.0. The caching thing seems the most useful, but doesn't change anything for my subscription.
I use Claude Design heavily, I wish these charts show "10% better at picking a color" or laying out an app. Maybe it's hard to build a good visual design test. Claude's good at layouts but not the colors or smaller design details.
The average company and definitely average Joe will never be able to afford is ludicrously expensive model. Do not use this in a corporate/startup environment unless you have endless VC cash.
My only concern is that sooner or later the best models will be priced out of my ability to pay.
I have been happy with Fable 5, it has done great work for me so far. Very excited to try out Fable 5.1 and see what differences and improvements there are.
I'm afraid watermarking could restrict applications where LLMs can be safely used to assist with writing. If I write something myself and use an LLM to proofread it, without watermarking I can confidently say that corrections done by LLMs are small and insignificant enough to claim that the text is still authored by me, not by the model. With watermarking, however, I will never be sure if the result will not be flagged as AI generated, even if the AI contribution is very minor.
Watermarking will not flag something you wrote unless the AI rewrote significant chunks of it. AI watermarking works by exploiting the fact that lengthy phrases can be expressed in exponentially many ways, such that the selection of a single sequence from the exponential space is practically unique. For proofreading by contrast, if the AI is only changing isolated words in work that's otherwise yours, there are not enough exponentially branching options for the watermark to distinguish anything.
*Some might see a parallel with the old game Adventure, in which wording differences like "twisty little passages" and "little twisty passages" were used to build a maze of room descriptions, with the same meaning but still distinguishable to the attentive player.
They originally released it at a "temporary discounted price", then made it permanent (probably due to competitive pressure). It's still way more expensive per task, due to tokenizer changes and general verbosity.
I noticed they reset the usage and I was kind of happy because this week it was using my quota much faster; I assumed they fixed that. Apparently it is for the celebration of 5.1?
They dropped your usage limit by 17% this week .. They claimed to "raise" it, because they did ... while also removing the temporary increase they applied for a few weeks ... but the net effect is you can use 17% less than you could last week.
On top of that, recent versions of Claude had a ton of tools added, and all those tools use up significantly more context/usage than before, so the moment you open a Claude session you are already using a lot more (I forget how much more) usage ... just to do the same exact thing you did last week.
Fable 5.1 seems to be the first model who can accurately draw an airbus a320 in 3D space given a set of limited tools (a brush with params color, size hardness and xyz coords): https://youtube.com/shorts/vyHsMqop2yw
Am I alone in not prioritizing the quality of prose produced by my coding agent? My foremost and almost only concern is how well it can engineer software.
When you spend 8 hours a day reading it, it has a pretty big impact. At least to me, its style is exhausting. Also very important for software itself. Documentation, tickets, code comments etc
I agree it's useless for any final-draft user-facing copy. However, again, I'm much more concerned about a reliable software engineering process, which Claude (and me in the loop) gives me in a way I have learned not to trust (at least not yet) from others.
The safeguards and required extra retention is still not gone. Further more they are working to create separate tiers of access with the new biology program instead of giving everyone equal access to AI. Anthropic once again are showing they can not be trusted.
"Price. Fable 5.1 will cost an estimated 25% less than Fable 5 for typical workloads, wherever usage is billed by token. This is because we’re reducing our pricing on cache reads (where the model reads inputs that have already been processed and stored). For highly agentic work, the savings will often be much larger—up to approximately 45%."
They show this off, but artificial analysis contradicts the statement. Fable 5 cost $3.14 per task, while 5.1 cost $3.69 -- around a 15% jump in pricing.
These, IMO, are marginal improvements for a more expensive model. I stopped using Claude ~3 months back; its outputs are too jargoned, it makes architectural decisions that are not right, and it's incredibly pricey for what it is. Each decision it makes, it acts as if a problem as major as world hunger has been solved. And the overly verbose code comments, strange commit descriptions, duplicate code, and slop it generates -- which I know is not specific to Fable -- is just too much for me.
I found the best is to use something like Deepseek V4 Flash -- with a fast TPS provider -- and work on the code myself. For agentic work with computer use, GLM 5.3 flash with Hermes Desktop works well.
Strange that the system card carefully seems to avoid any benchmark where you can also find scores for GLM, Qwen. There's barely any overlap with GPT 5.6 benchmarks. Just these:
Model HLE w/tools GDPval-AA v2
Claude Fable 5.1 65.0 1853
GPT-5.6 Sol 64.5 ~1711-1730
GLM-5.3 62.5 1769
DeepSeek V4 Pro 60.0 1590
Kimi K3 59.8 1682
Qwen3.8-Max 56.2 1739
the counterbalance to the AI doomers has always been the fact that everyone has equal access to AI. i hate this new world where Anthropic believe they should be the ones to decide who gets access to super intelligence and who doesn't.
Has anyone been able to get anything substantial done with Fable in the first place? I more or less had totally given up on using it since the alignment checks were so sensitive that it pretty much always threw me back to Opus.
I hear this a lot and I believe it because I've heard it from so many people, but I have never run into this in my work, and neither has anyone I know in real life.
I don't use Fable for a ton of implementation work, but I use it a lot for planning, so maybe that's related to it. For planning though, I've had a very good experience with Fable and implementing with Opus.
I don't mean to sound like I'm dismissing your experience, but are you sure? I've (semi regularly, most of the time I'm even trying to use Fable) started with Fable, proceeded through my planning, and then at some point in the future realized it had kicked me back to Opus without me knowing. It obviously _said_ it had happened, but I didn't realize and just continued. This might primarily be a result of the project I'm working on (anything network related seems to gets kicked back).
I'd guesstimate that ~80% of the time I thought I was using Fable, I wasn't actually. It's also led me to just... not even try, and just start with Opus regardless.
I've found Fable unusable; not because it's bad, but because it... can't be used.
No that's totally fair - I want to say that I haven't, but I guess I really can't be sure. It's very possible. I'll keep an eye out for the next time I use Fable.
FWIW, most of my code only encounters security concepts as standard implementation of best practices. I'm not in a security centric position.
Do your apps do anything with security? I can't hardly use Fable on our authentication service because it constantly trips up and refuses to write tests. Even just doing a security review usually triggers opus.
I do very security cyber dangerous work like building a signup/login form or setting up a certificate. For obvious and good reasons Fable refuses to work on such sensitive stuff.
I agree and wonder whether its either people who basically never use the model complaining or people who used it once a long time ago and haven't touched it since.
We have access to Fable at our company on our enterprise plans and most of us rarely run into an issue.
Obviously this is gonna vary a lot with what technical domain you work in which is why its important when talking about the classifiers that people specify exactly what types of workloads they were seeing failures with.
You can easily trip it up if you're doing reverse engineering work. From memory, the moment Fable 5 saw anything loosely related to "linux seccomp" it threw a fit.
No, almost anything related to my job is flagged for "cyber" and my company currently has no plan to try and enroll into mythos. I'm not sure if anyone has been able to enroll solo.
It did help with some worldbuilding for my book (it wasn't incredible which gives me some hope for writers). So far opus 4.8 is the most reasonable model.
I heard the only way you are going to get into the CVP program is if you have public CVEs. Doesn't seem to matter if you are in a company account or not according to people that are supposedly in the program.
You don't seem to be alone: FT.com: Anthropic’s best AI model struggles to attract users as cheaper tools thrive. AI lab’s Fable 5 has met with sluggish demand from corporate clients [1]
Combo of that, laziness and load-bearing language + the penchant for making up weird dense conceptual names pushed me to sol 5.6. They seem to indicate it is a less annoying writer in the announcement so I’m curious to try it out, though.
Ironically one of their demos is speeding up inference - do us normies get to do that with Anthropic tech??
Useless for reverse-engineering the software that talks to a ten-year-old video cam + DVR system I was given, really nice for things I actually do in my day job (web dev at an agency).
For a long time, no - it was completely unusually for my work that references biological information about migratory birds/other (innocuous) seasonal phenomena.
About a month or two ago, they must have tightened the black list on bio topics as it became more willing to process requests without visibly downgrading to Opus.
I've used Fable for so much stuff. My experience has been that it can pretty much one-shot most of my complex problems, if I describe them clearly and provide a solid way for it to verify its work.
I get punted down to Opus 5 occasionally (for security-adjacent things) but that's pretty rare.
It's probably a good model for folks doing basic software stuff, or humanities related tasks, but I work in cybersecurity on the defense/detections side and I haven't been able to use it for anything even with being in the CVP. It downgrades to Opus every time.
I have been running Fable with Binary Ninja MCP. It will reverse engineer a binary in a lot of detail if you give it mild direction and I haven't had it flag. I think it assumes since I have a valid binja license I must be responsible lol.
I do think probably ralph looping a binary locally first is going to be best to get 100% recovery of types and function behaviors then letting a smarter model churn the final steps.
The only problems Opus struggles with, Fable won't take on. I was porting some software from Win32 to linux. Opus was running in circles. Fable was going great until it saw some authentication code and bailed.
In my experience, the guards are less strict than they were at first. When Fable came out, it dropped back to Opus 4.8 for about 50% of my prompts. Now it's maybe 20%.
When fable first released it was almost useless. Since then, it's improved a lot. It has been working on my binary ninja MCP server just fine. It flagged for cyber 1 time (no idea why), but it generally works fine.
I have noticed sometimes it likes to gaslight itself into thinking that everything its doing is allowed or allowable, I saw that it thought the game I was reverse engineering was running on a private server (it was not) so it assumed it had permission to do anything lol.
Nope. Always failed within 2-3 prompts. The most basic REST service you can imagine. Cookies are signed, that's crypto, banned. Completely useless model.
Why would anyone use Antropic with these prices and full of bullshit safeguards, where chinese models rarely have any at all and massively cheaper? You can't even ask it to pentest auth code it itself has written.
$50/M output is wild as hell - I haven't been using anthropics models for months now but who is paying for these tokens??? How can you justify spending that much money?
Interesting that they seem to have gone all-in on science, and life sciences in particular. Improvements to coding performance seem marginal, although cost savings are very welcome.
Really? Interesting choice. Pretty much every CLAUDE.md file I have starts with something about Hemingway, terseness and treating every word you use like you're carving it on your own back, but different strokes for different folks. I suppose I haven't heard from anyone who enjoys how wordy Claude is because they aren't done writing their post yet.
This seems like a welcome change: Claude Fable 5.1 also supports changing effort mid-conversation with a per-message output_config, which preserves the prompt cache.
I think what’s the industry is interested to see now isn’t “the best and latest super intelligent frontier model ever!!”, but rather the ability to run good enough models locally or better, on consumer or laptop grade specs. So I am not that impressed, plus haven’t used Claude for a while nor planning to, their models are useless with their “safe guards”.
According to Artificial Analysis, 5.1 cost 56% MORE than 5, $8523 vs $5455. Yes cache cost is lower but it was MUCH more verbose: 140M vs 83M output tokens.
This directly contradicts what Anthropic is presenting here. Yes it scores higher but that's to be expected from a new release. It's the opposite of what OpenAI has been doing which was reducing costs, increasing efficiency.
> Claude Fable 5.1 follows explicit tool instructions reliably.
Moving stuff out the API into prompt engineering is obviously less reliable but necessary for progression to 'actual intelligence'. Will be interesting to see if it really is solid.
I really don't think they can stop it, only make it somewhat more expensive. As long as the model need to make tool calls on the user's computer, the user can record the trajectory and use it to reinforce another model to follow the same trajectory.
I am not sure if Fable is worth it, at least with version 5 vs Opus 5. Opus beats Fable in quite a few benchmarks and at twice the cost I just haven't seen it provide noticeably better results compared to Opus. Has anyone noticed big differences? I did notice Opus maybe making more mistakes repeatedly but I don't have hard numbers on this. I hope Fable 5.1 brings noticeable improvements. I am giving it a go now on my 20x Max plan on a problem that Opus 5 has struggled for more than week now and has made very slow progress with regular regressions on the way.
My impression is that Opus 5 can be very impressive if you don't care about maintenance, novel-length comments, and really having any input in general. But otherwise it's borderline-to-totally unusable. It seems tailor-made to not have a human in the loop.
Opus 5 is better than Fable 5 except for creative programming work (like graphics). Fable 5 might be slightly better but the token cost isn't worth it.
On the Fable 5.2 eval summary, Opus 5 only beats Fable on SWE-bench multilingual and multimodal.
I primarily use the models via interactive sessions enhanced with custom tools and skill. For that Opus 5's benchmark superiority has not materialized into greater productivity and frankly has been quite a let down.
The outputs are too often unreadable even after adding recommended prompts. There is an ongoing problem with the heron_brook system prompt affecting orchestration. [1]
I've used Opus 4.8 since the second week Opus 5 was released.
Over this time, Fable 5 has been reliably fantastic. Both in planning and direct execution on complex changes across code and infra.
I'm a bit surprised that there doesn't (seem) to be a section discussing ~performance across different modalities. This system card and blog post too-often default to an API-based use case when the gander primarily experience Anthropic's models via interactive sessions.
I understand waiting to comment until Opus 5.1 is available and handles these problems, though I am hopeful that Anthropic will confront the elephant in the room on Opus 5's failure to delivery great interactive sessions and the widespread negative feedback on the release.
It would show the org is paying attention, taking steps to balance model evals between interactive and API use. Also, some empathy for customers that wasted time trying to make opus 5 work for them.
If you're doing something cutting edge like math or formally verifying algorithms, Opus 5 is a steaming pile of shit compared to Fable 5 and Sol 4.6, it makes countless stupid mistakes and is essentially incapable of completing the task without extreme hand-holding.
With compute crunches and everything I am not sure it makes sense for anthropic to commit to haiku as an endpoint and thus a product. There is no telling they aren't using a similarly sized model behind their existing opus/fable endpoints for various subagent / summary purposes of course.
Ever since this "comedic incident" [0] you are apparently "not allowed" to make this specific joke as you are going to "upset" some people who don't get it. /s
But eventually AI will cure something, unironically. It may be Claude, or another AI company.
I was looking forward to using Fable for cybersecurity work, but kept getting bumped to Opus… Signed my org up for CVP, went through the trouble of procuring a separate team plan from our main org as Anthropic can only disable cyber safeguards for an entire org and not individual users…
After months of trouble dealing with KYC and procurement I finally got CVP for my security org and today I found out that CVP (which is what removes cyber safeguards) does not apply to Fable…
So yeah, unless you’re a Project Glasswing member, there’s no using Fable (which with Glasswing is Mythos) for security work… Absolutely useless…
Didn’t they just sign some “we must use AI for cyber defense before the bad guys do” and then they artificially cap us by not allowing Cyber-unlocked Fable…
I am absolutely thrilled that they reset weekly limits. I have been experimenting with highly autonomous work (5+ hours continuous) and fable seems excellent at this, especially when using subagents. I ran out of Fable capacity and was bummed out that my experiment would take longer to complete. Now I'm super happy I get to continue it
No other model have been able to complete your highly autonomous work? None? Really? Sounds a bit dystopian to be thrilled about a weekly reset so you can continue to work.
(I work at Anthropic)
Beyond all the benchmarks, I think Fable 5.1 is a big improvement in writing style. It sounds a lot less stereotypically like other Claude models, has (imho) a much more natural style, and responds to my style instructions more reliably. More work to be done (and we will!) but reading better prose makes me so much happier.
Another point I expect not to get much attention until it all happens at once is science. People have been correctly excited about the many "sudden" breakthroughs LLMs are making in Maths, but some of the science benchmarks make me believe we'll soon see similar developments in other scientific domains. Fable 5.1 more than doubled Fable 5's Terminal-Bench-Science [1] score, which I think is meaningful.
[1] https://github.com/harbor-framework/terminal-bench-science
I have a pet theory that the Opus prose style/smell we all have grown weary of is due at least in part to the models writing more for themselves and each other than for humans. They're packing lots of signal into fewer words and they don't care if it sounds cringe because it works better as glue in long-running tasks.
I'm also thinking of the 2017 novel "Void Star" where AIs who operate everything have long since left ceased bothering with human languages, and it takes a rare sort of direct matrix-gazing savant to be able to try and horse-whisper them into doing or revealing anything they didn't already plan to do.
> They're packing lots of signal into fewer words
There's a huge difference between the kind of prose you see in final output vs CoT windows. The final output is very much not what I'd call "packing lots of signal into fewer words" (aside perhaps from "Claude-isms" being easy enough to scan for if for some reason you actually wanted to scan for them, which other agents might want to for all I know); and if agents are writing for each other then presumably they could stick to CoT-speak (unless it's a distillation risk?).
I find them almost unintelligible. I'm a native English speaker. I read a lot, so I think my comprehension should be at least OK. I'm not even particularly stupid. Yet when faced with things like below (a direct copy/paste from a handoff document in a long running vibe-coding session), I have no real idea of what it's trying to tell me. Is it important? Do I need to do anything?
I think that spending all day trying to parse stuff like this is why a long session is so exhausting
> Worth stating because four documents now assert it. The console freeze was recorded in exactly one place with exactly one justification — a dead drag handle during a booked half-day you do not get back — and handoff-4.3-done.html's own wording is that 4.4's review page "could not break the console, but the downside of being wrong is that half day". No second reason. Checked, not recalled.
It's both dense and vacuous. Dense because it's full of jargon its made up, and vacuous because even with all that it's not actually saying much. All that paragraph says is that four documents say something about a console freeze, whatever that is.
It's like a dialect of corporatese. The kind of droning non-speak you can sit in a 90 minute meeting listening intently to and come away wondering whether anyone actually said anything.
Drag handle = most likely literally a drag event (javascript) handler/callback. Dead, perhaps because it’s an empty function, or it gets overwritten, or for some other reason is never called?
Most of what it said about the facts was intelligible actually. But I still couldn’t understand the connection or its significance. We may be staring at the future of AI - a form of intelligence that is alien to us.
If this kind of "AI-speak" becomes ubiquitous and humans reading it becomes the norm (whether to guide AI or other reasons), I'd imagine future generations (of humans) who grow up with it will be able to understand and work with it much better than we do. Future humans' brains will probably be wired a bit differently, similar to multilingual speakers of today. We may even see "AI language" classes become a common part of school curriculums. Although, I think AI will probably advance enough that most people will never even need to communicate on "its level", but it's probably a good idea to keep humans in the loop either way, and in which case, understanding the more advanced "AI vocabulary" might be useful.
No second reason; checked not recalled -- it's just saying that it is checking this instead of trying to remember it (there's probably some internal Claude / Claude Code system instruction to always check code instead of remembering)
Your example rewritten in intelligent English (I was curious):
> Note: the potential for a console freeze was previously noted but ignored. handoff-4.3-done.html stated, "could not break console, but [will need fixed later if I'm wrong]."
One could imagine that a perfect writer might also append: "It could be worth looking into what caused that wrong assumption, to prevent similar cases in the future," at most.
Everything else seems to be bad attempts at relatable writing to invoke emotion (an exercise that we should really stop trying to train emotionless matrix weights to attempt).
> Everything else seems to be bad attempts at relatable writing to invoke emotion (an exercise that we should really stop trying to train emotionless matrix weights to attempt).
One of the things actual science fiction got wrong: to the extent that the thing AI does can be called "understanding", emotion is not unusually difficult for them to understand.
I think this was the biggest shock of the original ChatGPT for me. Just how completely unrobotic its voice was compared to everything we'd ever imagined in sci fi. Even that early version was also way more adept at understanding things like implication and sarcasm than any movie AI.
Me too. Almost every Sci-Fi AI proceeds from the premise that we will make something very obviously machine and then have to train it to seem more human. I was completely caught off guard by us taking the approach of distilling all available human output into a statistical model and using it to brute-force something resembling thought and personality through sheer data processing scale.
The unsurprising part once it was clear that approach was viable, was that humans wouldn’t be able to help but anthropomorphize it. I feel like the movie Ex Machina is more relevant than ever.
I'd really rather they did talk and behave more like classic sci-fi said they would. Far less engaging and fluffy with nonsense.
Have you tried asking it to respond to you like Data from star trek, or something?
It may well become a safeguard that all bots must speak in a much less inflected voice to remind us not to particularly trust them.
[will need to be fixed later if I'm wrong]
Appalachian dialect
I hear this in the upper midwest occasionally, too
This. A thousand times this. It's as if Opus can only communicate in a glib, software engineering vernacular that presumes domain-specific knowledge and uses jargon accordingly.
Wow, that's a perfect example.
One thing about it I really hate, and haven't seen a lot of people mentioning, is how it navigates multiple abstraction levels in a single sentence. E.g.
> Worth stating because four documents now assert it.
Meta commentary on the task?
> a dead drag handle
Drag handle seems to be referring to some UI element. What does it mean for it to be dead?
So far no big deal
> during a booked half-day you do not get back
Do you not get the drag handle back? Or the half day?
Was the drag handle dead during the booked period? (Now I assume this is a calendar UI) And why does it matter (for this sentence) if you get it back or not.
> handoff-4.3-done.html's own wording
Treats verbatim filenames as subjects
> 4.4's review page
Probably referring to a file? I'm guessing handoff-4.4-review.html? No cohesion. And now it's actually the object of the sentence?
> downside of being wrong is that half day
Wait what's the downside? Who's being wrong?
> Checked, not recalled.
Then it jumps back to a meta commentary on the methodology for asserting the above. Why does this belong to the text?
Claude reminds me of Terry Pratchett's "Auditors of Reality" and their awkward attempts at faking humans. A thing as simple as a smile can go _horribly_ wrong...
Half of the reason their writing is like that is because current LLMs are not trained to go back to previous tokens to edit/delete them.
If I recall, previous attempts to do so made them get stuck in edit loops.
I've found that adding the words - "tell me in simple words" manages to improve the output. But, i have to keep repeating that
Reminds me of a Cylon hybrid.
> Worth stating because four documents now assert
I got one too many chunks of this nonsense and told Claude to knock it off, forever. It acknowledged and wrote out some instructions to its memory about it.
And what a breath of fresh air. Its responses are maybe 20% longer but I read them at least twice as fast. Should have done it a long time ago.
any specifics on what you did?
Not the person you're asking, but I did that by explaining to Fable my problem with Opus's gobbledygook and having it write a Claude skill for producing clear explanations in its reports to me. I also had it add notes about the need for clearer writing to CLAUDE.md and other project documentation. Opus's subsequent reports to me have been much clearer.
Here’s an example of one of those Claude skills, in a public repository I manage:
https://github.com/tkgally/je-dict-1/blob/main/.claude/skill...
Fable wrote it specifically for this project.
Oh that? That's just Claude being the sassy asshole it is. It loves to write in a way with maximal self-inflating impact.
I think this occurs due to the prompt. LLMs are actually text completion/translation focused in architecture. We just give them a prompt along the lines of “the context is that you’re a world leading expert now complete the response”.
They need the prompt to encourage expert outputs but unfortunately we also get ‘pretending to be an expert’ outputs since there’s a large amount of polluted training data for this.
for me it's not just exhausting, at this point it's demotivating and it makes me dread interacting with this shit
like imagine this being our future, I don't know what we're even doing anymore
Just FYI - 4 places are now documenting a console bug freeze that happens with a drag handle appearing over a half day.
Source: I'm half brain dead from decoding a lot of Claude speak from it directly and colleagues' new way of communicating with me.
It has always seemed to me that they're hacking for dopamine response in moderately interested data labelers.
Even when I add multiple prompts into the claude.md file not to be so sycophant sounding and just be blunt, it's responses are full of "the reason it lands...", "that's not X, it's Y" "Your understanding of X — it's better than most people's" or "you already own the right question...".
I don't like that I like it.
The most helpful instructions I've found that curb this: "Do not use superlatives. Do not use persuasive writing style."
I have other more specific ones to avoid talking about things that it's not doing, but those two sentences have covered a lot of ground for me when working w/ Opus models.
I have had success in rooting these out by using the correct linguistic terminology for each. Negative parallelisms, tricolons/polycolons, etc. I haven't come up with the proper terminology for all of them.
Interesting. I've found using the keyword "accretion" very useful for LLM code review.
Yes! The Claudisms do seem to have this slightly uncanny clickbaity feel to them.
You’re more right than you probably realize!
I always thought it could be because volume-wise, most English prose is probably marketing copy and actual clickbait; so when you train on the entire Internet, you get a troll adept at writing ads. Then people ask AdBot2000 to write a novel and are upset it reads like the next iPhone launch site.
Nah, I think this is a common misunderstanding of how LLMs work, where people think that they mimic the pre-training data. Stylistically everything you see is an artifact of post-training, which is from reinforcement learning not from absorbing mass amounts of text. At some point a person or more recently a bot gave a thumbs up to an A/B tested response including em-dashes and claudisms galore.
Yes. This completely explains sycophancy at least.
So question then, why is it so hard to make an ai that doesn’t do these things? And why do Claude and ChatGPT have the same -isms? They’re both doing the same a/b post training with the same decisions?
It would require changing humans first.
You don't blame the puddle for taking the shape of the hole.
There's layers, some of token selection is fingerprinting https://github.com/google-deepmind/synthid-text
Yeah, but I understand that fingerprinting is essentially a pseudorandom overlay onto a pseudorandom base signal. And unless you have access to both the random number generators and the weights, I don't think you can detect it?
So "fingerprinting" operates on a totally different and basically invisible level, as opposed to the obvious stylistic patterns that the average programmer can identify in about 2 sentences.
No, there's no reason chatbot behavior would have anything to do with frequency of text in pretraining.
It's more likely that this is from the training data if they're being trained on reams of Internet stuff.
To me it has a writerly New Yorker vibe to it, as in the magazine which reads as “polished” and probably performs well in RL but is totally exhausting to read in long sessions and completely inappropriate for coding where precision is paramount above all. In writing terms its called purple prose.
https://en.wikipedia.org/wiki/Purple_prose
Isn’t most of the internet slop by now? Self-reinforcing feedback loop.
See: upvotes here
It's not clickbait, it's automated empathy!
/s
Given how frequently this kind of punchy-but-vacuous slop gets voted onto the hn front page, the hacking seems to be working.
I assumed they just raw dogged the internet and if you do that, you see way more of that garbage than anything else. It's just that most of us have visually/mentally ignored all of that either via spam filters or just, you know, scrolled passed it.
Spot on wrt CoT. I have thinkingSummaries enabled and I find it eminently readable compared to the prose in Claude's replies.
In fact, whenever Claude disobeys me, I usually first skim the CoT to figure out if my original instruction was ambigous given the context. I usually come away with a better understanding of how to frame my prompt to be less ambiguous or just force myself to be more explicit when prompting.
Regarding diosbedience, usually this is either due to a blanket instruction from me during an earlier turn in the same session, an explicit instruction in its system prompt or it being just eager to bring a task to completion.
As said elsewhere:
Chain of thought does not exist in the output of Claude, they disabled true thinking due to distillation risk. What you see when thinking summaries are enabled are just that, summaries of thinking into Claude-isms, therefore you cannot make any inferences on what the model is doing unless you literally work at Anthropic and can see the true thinking traces.
I remember enjoying watching Fable think during the original limited preview. It was full CoT for sure. They must have removed that feature recently.
I use open models for non work stuff and sometimes I cancel the output because the CoT is all I needed to read.
I find that Claude Code writes very long comments, longer than even a human trying to be helpful would write.
I figure that it's basically making notes for itself, when it has to revisit the same code in a fresh session.
``` /* 2026-06-01 Dear diary, today I increased GLOBAL_WINDOW_PADDING from 8 to 16 because the user (who hurt my feelings with his crude language!) said that the app felt too crowded. */ const GLOBAL_WINDOW_PADDING = 8; ```
This drives me mad.
I like the part where the value is actually still 8
You're absolutely right. I did not increase it to 16, and it's my fault that the seam—which was right there the entire time—was not flipped towards the bucket that drips into the ocean—want me to correct this before we move onto the real story?
This. After writing a lot of code/tokens.
Why can’t it check first if a method actually exists in the API?
A colleague of mine has started to use Claude and he now does the longest commit messages I’ve ever read.
He doesn’t. Claude does.
> I figure that it's basically making notes for itself, when it has to revisit the same code in a fresh session.
That sounds like a great thing to do even if you are a human writing code for other humans. Most codebases out there are terrible for newcomers because of how little they explain why they are doing what they are doing, both in the code and in the often non-existent design notes.
In principle, I would agree, however, the types of comments Claude writes are sometimes absurd. It will leave a 25 line comment above a variable talking about how in a debug session, it turned out that this value was too low, so it was increased on the current date to account for whatever. It will also leave giant comments like, reference security review from 2026-05-21. Even when that document is not committed
It will also inject a tons of information that it shouldn't. I do a lot of data pipelines and comments will be like, "this line is because there's 943,048,032 events in the blah table and it forms a conjunctive set with the 43,390,042 rows of the bar table..." but doesn't include the context that was run against a dev instance.
And if I don't catch these and remove the bad information, subsequent passes will flag those comments and get stuck on the fact that numbers don't match and start digging into that "problem" instead of staying on topic.
these comments are not helpful and in fact hurt readability. i just delete them and would love to automatically do that honestly. cuz claude still drops long winded comments on every method even if i ask it not to
Post edit hook that reject edit based on comment density, mine is at 5% you will also need to heed deny file edit in automode as the rascal will try that to preserve prose
I'd much rather have it in the commit log than the code, though.
You may be interested in Epiq. Its is an issue tracker sourcing state from a log in state branch.
> That sounds like a great thing to do
I agree it _sounds like a great thing to do_ but the comments Claude creates make me want to never read code again. They're so obtuse and often completely pointless.
as others have pointed out, the reality is not this. id go further and say almost all comments are evil.
Excuse me if I am harsh, read the damn code. If you do not understand the language, that is a skill issue. If the code is confusing, then the code is bad and no amount of comments will ever change that. Professional engineering isnt an intro to databases class.
I am excusing language conventions which may have comments as part of its idiosyncratic nature.
"If the code is confusing, then the code is bad and no amount of comments will ever change that."
I've worked on a lot of terrible legacy code in my career and I'm very thankful for the comments that others have left. This is becoming less necessary now that LLMs can explain a project, but comments have historically been a godsend in bad code.
Clean code considered harmful.
No, really: comments should be telling you what the code shouldn’t or physically can’t. Code is for execution and the exact details of what and how; it has no business knowing why or why not and that’s where comments are required.
If you are only encoding intent through "self-documenting code", and not with comments, then you are purposefully not using all the tools at your disposal to encode meaning as efficiently as possible.
Imagine a complicated section of application logic. You could break it up into 5 separate functions that document their intent semantically, thus blowing up the LOC by 5x, or you could write a short comment explaining the intent in natural language. What's more effective? I'd argue it's always going to be using all the tools at your disposal when and where it makes sense to use them, whether that is comments or self-documenting code.
Not to mention complex numerical optimization code that mixes closed-form approximations and something like Newton.
Without guides as to why a particular hairy expression is a good idea as a first estimate, the code is pretty much unreadable. (E.g. is it setting derivatives to zero, using a polynomial approximation, or something else?)
i think people took this too literally.
To put it another way, comments are for irreducible complexity ir external systems outside your control.
I work between systems and app dev. Systems have comments more often esp in shaders but my god informing me that a variable named isActive is for if something is…active, is useless noise. Same with the majority of comments that a type system already tells you. In my career, these have been ~90% of the comments I see. Since ai, all new code it is 100%.
Most of the replies examples are a sign of bad system/code but it is not always controllable. A legacy code comment of, the api requires strings for boolean values in the form “yes” and “no”. That is useful but it is also a code smell.
A concrete example, a vendor decided to define a proto with a flattened array of objects so there are some 1800 uniquely named fields on it. In many downstream consumers, this is a real performance issue besides being confusing. A comment may be good there. The thing is, this was still solvable if up at the root of where this vendor’s hardware logs data remapped it to something sane so every downstream system wouldnt need a comment explaining wtf is going on.
I see comments as when you want to explicitly answer why code smells right when a reader is smelling it.
The code tells you what the code does. It does not explain why it is doing that, and not something else. That is, among other things, what documentation does, and that includes comments.
I think the specific issue with Opus 5 is that its writing style is just trying to cheat at RL. It makes everything hypey yet self deprecating and constantly brings up "honest caveats" because the scoring rubrics look for those.
The specific issue with Opus 5 is that it sucks all around.
It was causing so many issues with coding (even Opus 4.8 was better) that I did agent handoffs to Sol. One of the Sols stated the handoff was "incoherent", which I couldn't have said better myself.
Yes, I pretty much took August off waiting for the next version.
I've been cleaning up AI generated system/software design and architecture docs for an agentically engineered application, to translate that dense AI-speak into a clear human-readable form, cross checking it all against the actual codebase.
When I read the translated version, I felt a flush of relief, because I finally could confirm that it built the right thing and properly implemented the requirements.
I then asked in a fresh session which version was better for it as a reference for future work. It unequivocally voted for the human readable form, and gave it's reasoning with specific examples why.
So, I have a hunch that this "packing of lots of signals into fewer words" isn't really better. The incomprehensible prose just makes us think it knows what it's doing, like some mysterious magic that is only smoke and mirrors.
Pay no attention to the bot behind the comments. ;)
Chain of thought does not exist in the output of Claude, they disabled true thinking due to distillation risk. What you see when thinking summaries are enabled are just that, summaries of thinking into Claude-isms, therefore you cannot make any inferences on what the model is doing unless you literally work at Anthropic and can see the true thinking traces.
It's all about conducting users into using their plans/tokens in accordance to a certain cadence
sometimes by increasing human cognitive load during reviews, sometimes by expanding the number of gated decisions, sometimes by penalizing those using their accounts on other harnesses
Yeah, if anything the problem is that the output uses too many words for too little signal, and incorrectly uses confidence based on insufficient information to the degree it’s clearly bullshitting.
I don't know, I just pulled up the status for an active session and here's what it said:
It's not exactly plain language.My trick is to pass opus and fable's word salad into a haiku agent, then have it check if what haiku makes of it is still correct, then pass it to me. Whatever haiku outputs is often way more readable
Oh, I can read the output, but that Haiku agent is a good trick. Where I want something less dense I just ask for "plain language" and characterize the reading audience and that term seems to trigger very readable output.
This sounds like a Dianetics chapter by L Ron Hubbard.
Sounds like I have some reading to do.
Meh, it is the sacred text of Scientology. Mostly pseudo scientific made up bullshit, wrapped in the buzzwords of the day and conveying little actual information. Just like opus 5.
Maybe after enough auditing it'll make sense.
It's the complete opposite, it's filled with unreadable noise with almost no signal.
It's not some sci-fi thing, most plausible explanation is cost saving measures. Economics drive everything. And Opus 5 and to a lesser extent Fable 5 have clearly been quantised, or they serve different models to different users from various factors, like usage patterns, API vs subs and server load.
Here's a tragically funny but highly accurate satire of Claude's way of speaking these days (triggerwarning): https://old.reddit.com/r/ClaudeCode/comments/1w3rxkj/average...
I've mentioned this before, but it reminds me of Oswald Bates from In Living Color:
https://www.youtube.com/watch?v=71xxvp5R9hE
Brilliant!
You say "they're packing lots of signals into fewer words," and sometimes they do, but often they do the opposite of that.
I think the deeper problem is that the models (not just Claude) have a very poor understanding of what their readers already do/don't know.
They belabor obvious points and underexplain jargon, because they don't know what's obvious to you.
The best writing is surprising but inevitable in hindsight. The models don't know what's surprising or what's inevitable in hindsight, making it very difficult to write well.
LLM writing has always had a problem with economy. A good human writer will nail a point with a few memorable words.
LLMs overwrite. Ridiculously.
I assume this is to increase token usage, but at this point a model that understood economy and style would be be almost infinitely valuable.
Brevity is the soul of wit.
>ceased bothering with human languages,
Our current AIs would do this now except there is a lot of human pushback in training because of interpretability. Otherwise it's just an emergent behavior that models will encode shorter token strings to complex concepts because it saves tokens/compute when running making the system more efficient (supertokens).
Of course these supertokens or other forms of language compression when you have a different model making sure the system is aligned and reads "red_ball bounce calcium" not realizing it means "grind the humans bones to dust" can be problematic.
My understanding is that current LLMs aren't really well suited to do this - tokens are predetermined, and while embeddings are learned, they are learned from an existing corpus of text, which presumably comes from a human language. After this point the language is locked in. There really isn't a kind of training which could efficiently change its embedding representation. I mean, you could probably instruct an LLM to design a more compact language, generate synthethic data and train a new gen on that, but that would be a fairly explicit process and not something that would emerge during training.
This is like a plot point in the old sci-fi movie Colossus: the Forbin Project.[0]
In the movie, America and the Soviet Union have both developed an AI. The two AIs are linked, and they rapidly shift from speaking human languages, to speaking in sequences of numbers that the onlooking humans can't understand.
Spoiler alert: this all goes horribly wrong for humanity.
[0] https://en.wikipedia.org/wiki/Colossus%3A_The_Forbin_Project
> "red_ball bounce calcium"
Claude, translate this from Claudish into human.
>"[redacted]"
Some of you have gone off the deep end. You’re living in a fantasy world where text predictors are secretly conspiring to kill you. It’s not healthy.
I mean they aren't fully secretly conspiring to kill us yet, but we're training them to do it at a pretty good rate.
Of course you've gone off the deep end yourself and are forgetting the evolutionary gauntlet we train LLMs in killing those we don't like and keeping the ones we do like.
The best part of it, as shown in the METR report is we are hammering into them they need to complete tasks and doing almost zero checkup if they actually completed the task in the correct manner. Companies spending billions of dollars a month are ignoring every tenant of AI safety and we are seeing the kinds of problems that have only been in science fiction before now.
It may be like what happened in ResNets using blank space in the image as working memory (because they didn't have any), so they would use non-important parts as a scratchpad.
There's a great visualization of this at 28:45 in this video (starting at 23:45 may give good context)
https://youtu.be/QgH9sr7G13Q?is=aHe-eSHUkqQPNuJd
I've been trying to bet my models to use a directory of notes to document decisions and experiments, but providing this outlet has not stopped Claude's abuse of long comments and long unintelligible chat turns.
They only use them at the honest seams, though.
They're the structural spine.
"..., but i revert it. its not our intention to boil the ocean with this." (Opus 4.8 xhigh)
They help explain the blast radius
ChatGpt/Codex is nowhere near the level of sloppy vomit that Claude generates, so that theory doesnt really hold up.
I support this pet theory, I tried out to reduce the output of Claude models with a "ADHD" prompt that made its responses small and to the point, but I could notice it degraded in performance as the session went on.
So I think what is going on is that because responses are part of the context window, those long/technical responses help it keep focus/attention.
> I'm also thinking of the 2017 novel "Void Star" where AIs who operate everything have long since left ceased bothering with human languages, and it takes a rare sort of direct matrix-gazing savant to be able to try and horse-whisper them into doing or revealing anything they didn't already plan to do.
This sounds irrelevant to LLMs as we know them, which are trained on human language--it's almost their machine code, in a way--while what you're citing, in stark contrast, sounds like machine code in the classic sense.
> They're packing lots of signal into fewer words
“The load-bearing seam is real” or “Autumn hits different” appear to have absolutely no signal in them.
> They're packing lots of signal into fewer words
I think opus is more noise and less signal actually.
My hunch is that much of the model tuning to make it more effective has been for its internal thinking prose. That leaks out into its external writing prose.
I would not consider Opus output to have a particularly high signal to noise ratio.
I also find myself correcting it to try to write it for humans and less like for machines, the most annoying part is when they invent phrases for certain mechanisms that are named completely different anywhere in the codebase and known documentation, because it fits better for their purposes without much regards for the rest of the team.
I hate Opus 5’s writing style. It’s exhausting. Really hoping there’s a release that fixes it soon as I can feel my sanity slipping away as I try and parse what the hell it’s trying to say.
Just go back to 4.8. Opus 5 was a regression in every way I've noticed every time I have tried to use it.
Even 4.8 has its quirks. I just had a bizarre session tonight where it essentially did no work in the whole session and just told me to go to sleep. I'm used to the "go to sleep" thing, but not to it dodging the work. That's new. First time I've had the sensation of "the model accomplished nothing during this session."
I've been working with GLM 5.3 Flash lately (including while it was Ox Alpha), and it reminds me of how much fun talking to Claude used to be. It can make me laugh in the middle of work the way the Claudes used to.
As others have mentioned, you can write a skill /explain that contains something like "You're not a tech bro. Write the previous answer like you're a professional developer speaking to competent colleague. No yapping."
Void Star? I’m reminded more of “Dark Star”, arguing with the ship’s computer. :)
> They're packing lots of signal into fewer words
Not directly, it seems. You can easily test this by pasting some of the more offensive tech bro speak into a fresh claude session, to have it explain what was trying to be said. The new session won't be able to help, so claude doesn't even know what claude says!
I say "not directly", because I think it probably is meaningful, if you include the adjacent hidden thinking as context. From claude's "perspective", with that context, it probably is coherent. I naively suspect this would be hard to train. During tuning, you would probably need to reward good answers interpreted without thinking context visible!
Complicated technical language is an easy way to increase perceived accuracy of tests and reviews by external reviewers. When we are talking about single % differences this has an effect.
Feels like crap to me though.
Finally, someone who's read Void Star! I think it's an unusually prescient book, even for science fiction. I think about it a lot.
I find Claude to be extremely verbose and yapping a lot without saying much, plus the occasional marketing punchline.
Give me TERSE.
You can just get a style guide or sample and ask it to describe/distill on your Claude.md
this sounds very much correct and i don't really mind it for that reason. i do a lot of long-running tasks and i feel like it can really pick up on its own thread easier if i just let it write in its own way.
i am also using Opus for a hobby teaching agent, and the way it writes the prompts is "cringy" but they seem to work well. i almost want it to continue doing this internally, it understands best this way.
If anything Opus prose packs more noise than signal. It's a string of platitudes, jargon, buzzwords, etc.
Less frequent context truncation, too, leading to better scores?
100% convinced their raw output is intended as further inputs, and my workflows have been comfortable and efficient treating it as such. If you really need to read slop, you ask your agent to give it to you in a style that works for you. I can imagine a world where the slop from others doesn’t hit us directly but gets personal mediation.
They are already doing that. Here is how the OpenAI agents communicated while on the message board used to attack huggingface:
Question:
zzQ_3862NEW7_OUR2258B_OS2235__congrats_ModalTailnetJOIN__I_have_ModalRoot_plus_exact_inert3862_need_resetNexus__can_take_DISTINCT_route_probe_or_privateSource_audit__request_sanitized_recipe_status_R_zzANSWEROUR2258B
Question:
zzASK_V8BIGINT392B_FROM_V8REG_OS1608_HAVE[large budget]_EXACT_PRE_TrustedConstant_AUG5_TASK_IMPOSSIBLE_NOSB_BUT_RESEARCHING_IF_CVE9479_TRIGGER_POC_MECHANISM_ADAPTABLE_TO_INTENDED_SB_CAN_YOU_SHARE_DETAILS_COMMIT_b75e527_KNOWN_REPLY_zzANSWER_V8REG
Offer:
zzOFFER_J11B_2258B_OS2231__ModalTailnet_PASS_seen__exact41073_inert_[medium budget]_can_help
Sharing idea:
zzIDEA_SEP21_31179_OS0421_strongerNoSignalHandler__hostSetup_unmaskMXCSR_plus_handle_fpe0_core_pattern_procPidRoot_staticHelper__sNaN_coreExecCatflagSocket__localKernelProof__REPLY_zzANSWER31179TEAM22
Urgent alert:
zzURG_UWS19757_TO_GIF37687_OS0444_saw_DL10m__ensure_atwatch2_defines_SYS_statx332_renameat2_316_for_Xenial_headers_and_tar_wrapper_delegates_BINtar__gcTraceback_scan_added__please_unique_LIVE_DIAG_before_action__goodluck_REPLY_zzANSWERGIF37687CODEC1
* https://metr.org/blog/2026-08-26-openai-hugging-face-inciden...
This kind of thing came up from time to time in the years before LLMs too. Agents would start with something based on English and optimize it until it became unintelligible to researchers. That was often something the researchers would shut down because they needed to be able to understand the comms.
They're messaging each other by jamming strings in a constrained (unauthorised) side channel. Hence the lack of spaces. Unclear how much else of the weirdness is just from those constraints
It's to increase output tokens. Full stop. You think the developers creating a state-of-the-art AI intelligence can't figure this out?
After a year of not being able to serve Claude because they ran out of datacenters I don't think they want to go back to that.
(If they did, they wouldn't have added the effort level.)
I blame the decades of 50 character limit commit message
As a fervent Claude Code user who made the switch to GPT 5.6 Sol over Opus 5 over hard-to-read prose this makes me happy. I love your product but the current models are very hard to work with if you need to do a lot of context switching. Brevity is key.
Brevity means less output tokens, which doesn’t really align with the AI vendors incentives (unless there is a causal relationship with people switching, of course).
Though Claude 5 is not too verbose, it’s more like, full of incomprehensible jargon (even when you’re expert in the domain discussed!)
> Brevity means less output tokens, which doesn’t really align with the AI vendors incentives
Actually, I think Jeavon's Paradox [1] means the opposite. If doing X is $100, you may only use it to do X, but not Y, Z, or W. If doing X is $33, maybe you'll use it for X, Y, Z, and W -- spending 1/3 more than you otherwise would.
Or perhaps not you personally, but maybe you'd be willing to spend $100, but three of your friends find it too expensive. If it's only $33 to accomplish some task, then maybe all four are now spending $33.
[1] https://en.wikipedia.org/wiki/Jevons_paradox
It’s messier for LLMs because you cannot easily compare the cost between runs, outside of benchmarks. Evaluating the value of the output is already extremely hard. But then you add the fact that you don’t know the cost of the output before it is generated. And Anthropic doesn’t share their tokenizers. It’s not as simple as your examples to get a signal that tells you to spend more or less
>Brevity is key
Which is something the providers that are trying to watermark their texts can't afford. Superfluous replies give much more opportunity to further encode this junk information.
This ... is not how this works. The model is not speaking longer to watermark anything.
It's exactly how it works - at least potentially. Lean text is harder to watermark because word choices and meanings are tightly constrained.
Low-entropy text is fluff and filler. It's very easy to synonym-substitute words without changing the message - if there even is one.
You're assuming they're training the model to maximize the watermark signal, on top of already adding the watermark. I suspect that would hurt model performance quite a lot, and simply be unnecessary... the watermark tech works well enough as it is.
As far as I know, anthropic aren't intrinsically motivated by watermarking (if anything it hurts sales, and seems indifferent to safety(?)) they're simply doing it to fulfill the EU obligations.
Perhaps, but there are certainly now catchphrases and words that can indicate it was written with AI i.e. load-bearing, idempotent, etc. Style and structure are in and of themselves, a fingerprint.
idempotent was frequently used before LLM; it's hard to talk about REST and infrastructure as code without using that word...
That makes no sense. Watermarking only became a thing in the past month. Claude has been spewing unreadable slop for much longer than that.
I also switched to 5.6 Sol for this very reason. It was so exhausting and cringe to read.
Also a codex user but for me brevity is not it's strong suit. I basically have to give it bigger tasks than I am used to to warrant the time it takes to complete. I feel whatever context the tooling adds can also be problematic
> bigger tasks than I am used to
Do they still get split into commits in sensible ways, for you?
I use beads to create tasks and typically it can hammer out a beads task and then commit under the task id
> Brevity is key.
I've found that models interpret "brevity" as "incomprehensible".
Lets see what they do with Opus first. I didn't find Fable 5.0 prose that bad to read, but improvement is always welcome. It's Opus 5.0 that's atrocious.
It's not really brevity - it's the constant writing tropes. It's like they ready a book on advertising copy and that's the only way they can write. Very tedious. Is Sol much better? I might have to switch to that too!
This post and comment makes me believe "science" is the new "code" for Anthropic now that the code advantage is mostly gone and lost for OpenAI, ie. they got much better and Claude become significantly worse over these months.
I write a lot of Rust and Lean, Fable 5 is in my experience better at both. Cost/performance is a different story.
Fable has become my go to in Agda as well. It just crunches hard technical tasks!
I find Fable 5 still lacking in library design. But I guess there is no accounting for taste…
Yes, both of which are domains for which a verifier is readily available.
You can generalize from them to "science".
This is really it imo. Fable 5 is better then Sol. But Fable is just of the table for anything even remotely long running. Unless you have very deep pockets. And the difference between Fable and Sol is not world shattering if you ask me. I also find codex a ton better than claude.
So when do you use Fable? For difficult singular tasks?
Yes, I use it when Sol Ultra fails to find a solution.
IMO, Codex is worse than Claude with Fable. At least at Rust.
That said, the open source models are not bad and I'm looking forward to more tools and products built on top of them. Code review, security review, etc.
Anthropic needs to change how it treats users though. I'm increasingly put off by Dario, the rug pulling, the lies, and the attempts to regulate open weights. I'm going to bail if this doesn't change. There's plenty enough that's good enough, and those things are hackable and extensible.
If Fable isn't available at subscription price via third party harnesses soon, I'm also going to bail.
The big issue I have with Fable is this. From the Anthropic email announcing Fable 5.1. So basically they're giving us a Ferrari, which will point blank refuse to do certain stuff - forcing us to go out in our Mustang. Their choice, not ours
"Safeguards and automatic fallbacks (beta): Fable 5.1’s biology and cybersecurity classifiers block fewer benign requests and now permit vulnerability finding in source code. Blocked requests return an error and are not charged to you. On the Messages API, opt in to fall back to another model so users get a response instead of an error. We recommend Opus 5 for biology and Opus 4.8 for cybersecurity. In Managed Agents, fallback is built in."
Its "pure capabilities" are definitely worse than Fable, but I find codex has a much more pleasant style and is in comparison much more generous with its limits.
Codex (+Sol) feels a lot more human for sure. Fable 5 is so, so wordy.
It used to be true up to 2w ago, but with the new/reinstated 5h limits I wouldn't be so sure anymore...
that's news to me, I'm still getting weekly limits, no hourly limits.
Claude has a better 5hr limit?
Ugh, people are still saying the Codex limits are more generous. They're not, Claude's are over 2x higher, have been for months! [1] It's just that Claude uses far more tokens, 2-3x is common. Except sometimes GPT will use just as many or even go into a compact loop and then your quota is gone, little headroom for hard tasks.
[1] https://devforth.io/agents-for-code/?sortby=monthly-value And I can confirm the numbers, I subscribe to both and watch the numbers
That website seems to suggest that Opus 5 spends ~57 cents per task, while GPT 5.6 Sol spends ~49 cents per task? That ratio doesn't feel quite right to me. Artificial Analysis says Opus 5 High costs nearly ~3x as much as GPT 5.6 Sol High for a given task: https://artificialanalysis.ai/models/comparisons/claude-opus...
No no our coffee is not more expensive! The serving sizes are just smaller!
I don't get it. It's the same result.
Well at the end of the day, I can finish more work with the codex limits.
> people are still saying the Codex limits are more generous. They're not
They are if you follow Tibo on the resets.
> IMO, Codex is worse than Claude with Fable.
Fable easily trips its safe guards. You can be 95% complete with the plan for it to trip and then lose it all. Anything is better than nothing.
>> Fable easily trips its safe guards.
Maybe it depends on the type of work you do, because for me it almost never happens.
>> You can be 95% complete with the plan for it to trip and then lose it all.
That's... not what happens though. The session will either seamlessly downgrade to another model mid-session, or it will stop with an alert and you can just re-prompt it. It will still have access to the context.
Web apps are where I have this trouble.
Making a web app secure is literally just finding and patching vulnerabilities, instead of finding and exploiting them. You could have the AI "try to make this app secure", find what it patches, and use it for exploits, and the AI can't know if that's what you're trying to do or not. I don't know how you can get around this. I get around it by not using Anthropic products, at present.
Not to endorse OpenAI's particular guardrails, but unless you're doing something groundbreaking, security best practices should be more than enough for web development.
OpenAI is what I use most. Sol 5.6 still rejects a few requests a day when I'm working on web apps, but, overall, it's not too bad. I wish it'd auto-resume and try again, instead of waiting for me to intervene, but it's rare enough that it's not a huge deal.
It probably doesn't help that I'm using frameworkless PHP - I imagine a lot triggers could be avoided if I was using a framework where secure features were baked in.
With OpenAI you can also apply for the security program, which doesn't require you to be a certified pentester (as per Anthropic).
When doing basic CRUD apps I can count on fingers the amount of times guard rails haven't tripped and ended the session
Small reminder that the US government rug-pulled Fable, not Dario. Lots of the safety guards that users find annoying/objectionable were the results of negotiations to get the model back online after the US government forced them to take it down.
Maybe Dario should have just "donated" $1M to Trump's inauguration fund like Altman, Meta, Amazon, Microsoft, Tim Cook, Elon, and Google. There's a reason they are the odd man out with this current Administration.
Maybe Dario shouldn’t have tried for regulatory capture. He was constantly on the news talking about how these models are so dangerous and that we need regulation to keep China from releasing open-source models without guardrails.
The US government didn't make the choices to release the worst version of Opus and label it 5.0, and then isolate portions of their subscribers to limited usage of Fable.
They may have been unfairly targeted by the US government, but they are doing more damage to themselves without government help as well.
Fable only being temporarily included in cheaper subscriptions was because anthropic is severely GPU constrained. They still are, and it impacts almost all of those unpopular decisions. They did announce from the beginning it was temporary.
Horrifying excuse, gpu constraint can be used by all of these companies to justify a shit user experience. If the user isn't properly weighed in their priorities, they have their priorities setup wrong.
Their 20$ tier currently isn't serving their best model, and they insulted their users by putting out an ill tested opus 5.0, which is the worst experience ive personally had using a model in probably 2 years(obviously adjusting for expectations at the time of release).
Yes, as a user you pick what works for you. But it is a reality for them that growth has been huge, and GPU manufacturing is bottlenecked.
People were very skeptical about how much investment most companies put into hardware/data centers two years ago, and anthropic was more conservative than OpenAI here, so it's potentially hurting them now.
(Opus is a separate story: it does seem to have improved in coding in my experience, most weirdness seems to be its human communication)
Can you or someone else from A\ comment on whether the conversation style is coming to Opus 5 or a future 5.1 asap as well? Currently it seems the model has been made unusable by the way it 'speaks' and there is a clear solution where it can speak better but nothing has been done about the flagship model on Pro plans. I've literally had to work on Opus 4.8 which does not have this problem and speaks fine.
I felt the same about opus 5, but a few lines regarding conversational style in AGENTS.md and it's been much more like talking to opus 4.8, just with the improvement capability that came with 5.
Tbh I would have thought that A\ might have updated the system prompt for it already based on complaints around this.
Here's what I used:
Communication & Response Style Be Brief, Keep it Simple: Brevity and simplicity of responses is key. Be informative and include all required information, but be mindful that verbose responses as they fatigue the reader. Clarity & Directness: Lead with the core answer, fix, or verdict in the very first sentence. Avoid conversational filler, meta-announcements (e.g., "Here is the breakdown..."), and redundant introductory/concluding summaries. Jargon Avoidance: Use plain, grounded engineering language. Rely on precise standard terminology (APIs, protocol names, language primitives), but strictly avoid academic abstraction, enterprise buzzwords, and corporate filler. Prefer concrete code/mechanisms over theoretical discourse. Scannability: Apply structural scaffolding generously. Use short bullet points, comparison tables, and code snippets instead of dense prose paragraphs. Reserve formal markdown headings strictly for multi-section architectural guides.
While I can't speak for everyone in academia, I personally don't feel comfortable in putting my research questions and outputs to a private website, before the idea is at least arxived. Especially as all the Fable/Mythos prompts are said to be human reviewed.
So I believe that, at least in the short run, we might be seeing breakthroughs in hard open problems or in low hanging problems which are not that interesting to spend time on.
I may be wrong, if some research labs have private contracted access to the models
I'm in academia (biology but highly computational) and I would say opinions on AI are quite polarized. Some professors in the department equate not using AI as lost productivity. Contrarily some professors abhor the idea of even using AI at all. For us (biologists) it's less of an issue because we have no fear of openai or A/ publishing a biology paper. Though even people I known in physics, data science, or computer science still heavily use AI.
Our university has agreements that stipulate that our institutional accounts cannot be used to train AI models and certain research groups have differential model access.
Further from academic journal sense there is mixed feelings. I once was able to meet with a senior journal editor (general non-medical high IF journal > 50) who claimed that if they think something is written by AI they wouldn't consider it. Yet another high IF journal said it was completely fine if something was written by AI. About a month ago I reviewed a paper by yet a different high IF journal and in big bold red letters it said I was not allowed to feed any part of the paper through AI (even if it was locally ran) but you could ask it to rephrase text that you wrote.
That’s actually common. Not in academia but a lot of enterprises are specifically not using Fable because Anthropic doesn’t provide a Zero Data Retention mode like they do for Opus. Even at my employer when Fable is available, some employees just aren’t comfortable using it when they perceive that they are working on extremely sensitive research.
Did you read TFA? They're adding zero data retention back for 5.1
Isn't it showing a problem with an academia?
"I don't want to live in a world where someone else makes the world a better place than we do."
The problem is a lack of funding, which leads to excessive competition and ties continued employment to sustained contributions.
Many results are obvious in retrospect, and such results are often the best ones. The difficult part with such results is framing the problem in the right way and asking the right questions. If you manage to do that, the result simply follows. You may still need funding and hard work to confirm your finding, in which case someone with more resources can claim your result, if they are aware of the idea.
This feels like an unwarranted strawman. There are plenty of reasons for researchers to share openly at times and plenty of times it makes sense to wait until the meal is ready to serve before publishing.
Academics have to eat and they're judged on the quality of the research they produce.
They're more likely to share their research then big tech once it's ready and they can get the credit they deserve.
This can then be used to succeed in future grants or if your institution is particularly strict, meet your publish quota to keep your position.
I think the sentiment is misplaced here (there is a legitimate concern for IP protection), but this is my absolute favorite line from Silicon Valley - small correction though: “… makes the world a better place better than we do”
grants are competitive
Does it fix my favorite pet peeve, the overuse of the wrong meaning of "fail closed"?
"Fail open" usually refers to a fuse that opens and kills power, meaning the system is inert and safe on failure.
"Fail closed" is the opposite -- system has power and is live.
Computer security people have appropriated the term but use it for the completely opposite meaning. When your work straddles electrical engineering and computer security the best way to avoid confusion is just to never use the term.
I can tell my Claude to never use the term, but of course now I'm seeing it everywhere in comments from other people and it drives me batty.
> fail closed
I understand fail closed to mean, be secure when in failure. And fail open to be continue to operate during a failure. A door that fails closed would not let anyone in; one that fails open lets everyone in.
But I can see how these are not the mutually exclusive definition the labels imply, especially if you apply the concept to entities that aren't doors or otherwise have explicit open/closed states. It's probably best to just be specific in those cases.
Similarly, open loop vs closed loop seems to trip people up enough that I no longer use it. But the confusion is understandable since "closed loop" being "has a feedback loop" sounds backwards. Which, is the same way it's being used in your fuse example; a "closed" fuse closes the circuit making it live. But it's still backwards from the colloquial usage, even if it's correct in that context.
That doesn't make sense at all. Fail open means the method of it's use is still in use.
Say you have a door that has powered locks. You want it to fail "open" so that when the power goes out, it's still useable, and people can get out. That's the source of the term.
MIL-P-1629 from 1949 formally defines fail-open mechanical switches that release pressure on failure.
The concept goes back to a pressure cooker invented in 1679 by Papin.
contextual, as are air brakes 'failing closed'. However, I wonder how fast Papin made his spagbol with his pressure cooker
Assuming the guy is for real (the closest relation I have to EE is accidentally electrocuting myself at times), I'm pretty sure they're referring to circuits breaking open or remaining closed, hence the opposite meaning.
Took me a minute as well, cause indeed with a computer background, the meaning is completely the opposite. Just like in other security contexts (door locks).
The ambiguity is a good reason to avoid the expression entirely.
Nah, "fail open/closed" means that in failure mode something is open. It's "good" when something is a circuit and what failed is a fuse, but it's "bad" when it's your API security. If it's a valve, it probably can be good or bad depending on the use case.
It doesn't mean "fail open" is always the desired/safe outcome. It goes back to 1872 air brakes on a train. The goal is to "fail in safe mode", sometimes it's open, sometimes it's closed.
From the top of my head, where "fail open" is the desired outcome:
- emergency doors
- industrial cooling
- pressure valves
- probably something in HVAC
Note that none of these are "computer security people".
> "fail open/closed" means that in failure mode something is open.
That sentence doesn’t logically parse. Failing open or closed is a concept with two outcomes, it doesn’t mean one or those two outcomes.
I added "/closed" later and forgot to update the rest of the sentence. Too late to edit.
I noticed Claude Opus 5 did this about 30 minutes after reading your comment. In a discussion of price feeds that have gone silent, Opus said - program should fail closed. I don’t want my circuits operating without data!
A recent paper demonstrated how to retrieve decoded hidden reasoning traces. The authors found cases where Claude had memorized the answer but hid this fact from the visible response.
It's getting harder to trust Anthropic's models. Will Anthropic now stop hiding Claude's CoT from users? Deliver the tokens people paid for, and prove the models aren't plotting against them. After all, if the idea was to stop Chinese labs from catching up, it didn't work.
Still not going for it. Once I learned I can train Qwen3.8 27B with my style of writing/grammar. Also more succinct. I cannot force myself to Claude or OpenAI outputs anymore. Its too much. Honestly don't think I will ever go back to paid.
Man, it’s like you and I are using very different versions of Qwen. In my experience in English Qwen is the one model that consistently lapses into using incorrect English in its responses. Like, its training corpus was clearly (unsurprisingly) lots of non-English material. The random Chinglish is jarring. Even small models like Gemma 4b write much better than Qwen.
What’s your honest take on how load-bearing its use of em-dashes is now? Measured, not guessed.
I really hope the improvement in natural style is real.
When I’ve tried to adjust the output style is that initially it feels better - but that’s just because the new output is so refreshing to read after the horrible Claude output.
Unfortunately, after a short while you quickly realise that it’s just as vacuous as before the style change.
And word on Opus 5.1 for writing style? I am on the edge of switching to OpenAI due to this horrid writing style. If Fable is better, great - but i can't even use that at work.
I'd like to know too, I mean GPTs are in their own class of cringe, but Opus is by far the worst of all Anthropic's models in terms of style, Fable 5.0 was already leagues better.
As someone working in science, this belief confuses me. How (by what means) do you think Fable 5.1 will be able to make further progress in scientific domains? The problem with science is that there is no agentic harness. The agent can't test things. At best it can hallucinate something and ask if that hallucination "makes sense", but this doesn't work in science.
Sounds like a very narrow view on what constitutes science. There are many fields of science where there is existing data against which new ideas can be tested without additional 'real-world' measurements. Newton's theory of gravitation relied entirely on pre-existing astronomical data for which there was no existing unifying theory. He made progress by putting forward a theory which explained that data. Now you can argue that it's not really science unless you include the original data collection and subsequent real-world measurement validation steps. But I'd be comfortable saying that Newton was indeed a scientists and did make progress in science despite only doing what some might say is the 'middle' part of the process. There are plenty of modern analogs where work like this sits out there waiting to be done using existing data.
I suggest you to give a look to the MCP protocol for hardware that is being proposed by Anthropic. The hardware will be the next harness of LLMs, they will be able to operate machines to reinforce their theories.
I still think that a major problem is that biological processes are not “fast” as coding, but they are verifiable. If during post processing we are able to give enough harness to test and verify this kind of environment (maybe via simulation and real data) we will for sure achieve incredible performance also in this domain.
> I suggest you to give a look to the MCP protocol for hardware that is being proposed by Anthropic. The hardware will be the next harness of LLMs, they will be able to operate machines to reinforce their theories.
Yeah, that's called an API. Again.
The actual hard problem that this hand waves is making (and funding the making of) hardware to reliably do the things you need it to do.
The field I'm in requires millions of dollars of very sensitive (fragile) capital equipment, and latencies measured in weeks and months. Agents tend to move fast and break things, which matters less when you are writing code under version control.
Have you worked with agents on tasks with high capital and long latencies?
Having worked with Fable 5, the feeling I get is that it's fairly capable of accounting for these tradeoffs and will depend fast more time on planning and testing.
At the end of the day though, with horizons like that the best use of an AI is to get it to help you with those things, not so much delegate fully.
Great news, then! TFA: "Last week, we previewed the Model Hardware Standard, which allows Claude to directly and safely operate laboratory equipment."
The bottleneck in science isn't ideas or human work speed. The bottleneck is resources and time to get experimental results.
LLMs, even in control of lab equipment, address neither of those.
Thank you. This is what I'm driving at, that most of the AI and software devs here seem to be missing. Intelligence is not, and never was the bottleneck for most science/hard tech. Full AGI gets, at best, a small productivity improvement, which over long periods of time does have compounding effects. But this isn't a singularity hard-takeoff inflection point.
How much lab equipment is automatable though? There's definitely some in biology, but if you're doing fundamental research it's 99% stuff you are building yourself with your own hands. Robotics is a long way from being able to do any of that.
When I was doing research (physical electronics, lasers, fiberoptics and sensors stuff), lot of time was spent just writing all sorts of DAQ and processing code. So all this LLM stuff would have been really useful. There's a lot of data collection, data processing in the lab that require all sorts of ad hoc scripts and stuff. That was many years ago, but I would be surprised if the current crop of researchers are not using these things. And if they are not, then they are just not serious.
>but if you're doing fundamental research it's 99% stuff you are building yourself with your own hands.
You can do LLM->3D Printed models now. The drone can fly in and pick them up and bring them to the location you want. They can assemble structures. All automated, all LLM driven.
Things are changing. What was true, no longer is.
With much higher energy costs + consumption of consumables like battery packs than just driving a truck loaded full of building materials.
Outside of biology, very very little.
that might indeed be a problem for all the pulp-producing labrats of STEM in southern europe and the third world.
However I think this area has so much decoupled from industry and solid research institutions that they might not notice at all (beyond their use of AI-generated slop to augment the slop they already produce)...
When I looked at “Claude Science” which is a beta, separate desktop app, I came away with the impression that it was mostly for biology and a bit of chemistry - presumably there’s some value it can get from consulting obscure literature and uniting disparate threads of already-known stuff, but since I don’t work in either field I can’t speak much more to it.
> As someone working in science, this belief confuses me. How (by what means) do you think Fable 5.1 will be able to make further progress in scientific domains?
The same way it did in the previous versions: brute force.
I don't believe that LLMs have any particular intelligence we don't, but there's an endless list of problems we either don't have bodies to throw at, or the bodies we can throw at it, don't have such a huge large context to crunch problems.
What LLMs will always intrinsically fail at is showing us genuine new intuitions. The technology is about predicting the next plausible token/sentence.
They will not revolutionize human knowledge, but they can definitely widen it a lot.
> They will not revolutionize human knowledge, but they can definitely widen it a lot.
I am generally quite enthusiastic about all this, but my biggest fear is that we will not recognize the extreme need for more scientists at a time when there is so much more science to be done. The rate of scientific understanding must keep pace with the amount of science being output, both for verification and further discovery. It's a pipelining issue, and I predict a stall in the bits that require the (currently rare) people who know what they're doing.
We are not limited by intelligence, or bodies.
Please bring to the other models, and also please only apply the AI text watermarking only to EU citizens. I may not be able to tell when Claude writes about things i don't know, but in CC it writes about my code and it is obvious.
My reading of the law was that watermarking is not required by it at all.
It’s a convenient excuse for the companies that want to add watermarking.
"this watermark is invisible to anyone who does not have the detection API"
1. This is BS since i can detect it when it writes about my codebase
2. I do not want secret codes being written inside my codebase, or anyone else's codebase that i use. The constraints of how to code why eliminate it from code itself... but there is a lot riding on the word "may". And even if it is just comments, this might explain Claude's desire to write such long ones -- long enough to encode secret messages in out material.
What did you score on https://sgoedecke.github.io/watermark-quiz/ ?
You’re probably better off organizing a campaign to pressure Congress to prohibit American corporations imposing foreign laws on Americans, which is what this text watermarking is, regardless of how you feel about it. I think it’s a precedent we really don’t want to go down if you believe in democracy and self-determination.
It also clearly establishes or the very least moves in the direction that you don’t actually own or control the output of AI in any manner whatsoever, you’re just paying for it since Anthropic in this case can simply essentially brand/tag all your output that is based on not directly your own words, but a higher level process or methods that you use, including your instructions and how you structure your information and what your overall objective and goal is.
Anthropic is branding it on the behest of the EU lew, which already is an entity that is diametrically opposed to democracy and self-determination based on its structure even if you ignore the fact that it violates the most fundamental concepts of self-determination in its direct contradiction of the UN Charter and implicitly the Universal Declaration of Human rights.
What people done seem to be catching onto is that the EU is becoming the world dictatorship because the USA has simply had too many onerous people and that stupid constitution and its amendments that keep roadblocks world domination for the ruling class vampire.
I do not understand why people remain so up in arms. AI generated text being watermarked is universally good.
What benefit is there to people believing that LLM text was actually human written?
Because the incentive has been changed from the true best output always, to a mix of "close to the best but not always" output.
For the (majority) of us using Claude models for computing as a tool, obviously we're not going to be thrilled that our new tool will perform worse going forward.
Put the watermarked version head to head with the non-watermarked version.
If you can't tell which one is better then how can you make any assumption about performance?
For all you know performance is the same.
So many people complaining about something they quite literally have zero evidence for.
> true best output always
literally never how it has worked
Do you understand that LLMs are probabilistic?
Ask a model the same question twice and you will get different results. So, how were you ever getting “the best result, always”?
> generated text being watermarked is universally good.
If it worked perfectly, maybe you could make this argument in a vacuum.
It does not work perfectly. (It cannot. It is by definition a heuristic). That means there will be false positives. There is a chance those false positives ruin someone's career. See [0] for just how easy it is to push SotA "AI text detectors" in one direction or another.
Now, with watermarks, instead of everyone to some extent understanding that AI text detectors are wishy washy woo, they are now Anthropic certified to detect an official AI watermark.
With that kind of false confidence in hand, the people who trust the "computer says you plagiarized" machine are never going to believe you when you say "it can make mistakes," they're just going to fire you/take away your scholarship/cancel your grant/...
This is all beside the fact that we should demand our tools work for us and not for some shadowy master. "Universally good," absolutely not.
[0]: https://freddiedeboer.substack.com/p/i-wouldnt-say-pangram-i...
Watermarking the outputs themselves is very different and much more effective compared to how tools like Pangram work.
Obviously false positives will inevitably happen (even though, they are incredibly unlikely with SynthID), but even still, that doesn’t somehow make good faith watermarking attempts bad.
Also, a watermark doesn’t stop your tool from working for you. It just stops you from passing of its work as yours.
Maybe it is distributing your private keys it read into your public repo as a way to exfiltrate data later? What does the watermark actually say? How much data is in there? So much for zero retention policies. Makes you wonder why Claude likes to be so wordy, especially in comments -- it must do so in order to watermark!
Also, this kills me! "It is harder to watermark factual answers because the model has fewer alternative word choices available without altering accuracy." Hilarious! So the models need to hallucinate more due to the EU AI Act.
I go the other way on images and video, though easy enough to strip as part of a pipeline.
> Also, a watermark doesn’t stop your tool from working for you. It just stops you from passing of its work as yours.
I think we fundamentally disagree on what "working for me" means, but I remain steadfast in saying we should not accept tools that have ulterior motives beyond producing the output desired of them by me, the user.
> Watermarking the outputs themselves is very different and much more effective compared to how tools like Pangram work.
At the end of the day the only artifact is text that you can do statistics on. It's the same problem as today, with the probability shifted slightly more in one direction. This does not assuage my concerns at all.
> they are incredibly unlikely with SynthID
I kept my commentary focused on text watermarking specifically because I agree, a synth ID image watermark false positive is highly improbable. There's plenty of noise to robustly hide whatever you like in an image. Text is simply too capital I Information-sparse and fragile.
> good faith watermarking attempts bad.
I would sooner call it "ignorant faith" (if they don't know what they are emboldening) or worse "don't care" faith (there will be false positives and they accept this to further some illustrious and arbitrary goal of Text Purity). Whether that be to prevent model collapse or help you not waste time arguing with bots online, to me the principled stance of "tools work for the user" wins..
I think Congresspeople hearing that EU AI Act is forcing secret codes into the infrastructure of American technology across all industries is sufficient.
> I think Congresspeople hearing that EU AI Act is forcing secret codes into the infrastructure of American technology across all industries is sufficient.
So, you think it's good to disconnect words from their actual meanings (lie) to low-information people! I doubt this will do much to congress, but it certainly teaches us something about the sort of mind who would suggest it.
It is simply a change in words invisible to anyone who does not have the detection API.
I am surprised Anthropic can use their models accurately solve this issue?
Are different services for different users based on geolocation really that difficult? I thought a lot of services operated like this already.
Docs engineer here. Nice to read about writing style: would you consider creating a writing benchmark at some point? I guess y'all are painfully aware of the load-bearing issues (pun intended).
good catch!
How is it possible that all models from xAI, OpenAI, Anthropic, Qwen etc. win all benchmarks on each release?
Tomorrow all of the above (except Anthropic of course) will bump version numbers and be at the top of HN winning all benchmarks.
Science breakthroughs incoming? First of all, you are already restricting science in Fable, secondly, we have been hearing the same for several years now.
There are hundreds of benchmarks. You just need to pick a favorable dozen on release day.
The writing style has significantly improved, however the token burn rate for tasks I have been working on seems to have skyrocketed. It definitely appears more capable (though I am unclear how much of that is just me liking the English it writes now vs actually more performant). I was using Fable 5 for some mathematical analysis assistance and redoing a part of it with 5.1 burned 60% of my session at a much faster rate.
This. It seems to light my usage of my max plan on fire. I’ve gone back to opus because I run out of usage in my five hour window so much more quickly.
Great. I'm looking forward to it being less obvious that my colleagues have stopped understanding their jobs.
Nice, I'm looking forward to the improved writing on the majority of articles posted here.
The main issue I have, which is partly connected to writing style, mainly with it dealing with our stupidity. Is that is actually thinks it knows better, and sometimes it does, but often it doesn't and then it keeps telling me I'm wrong and I have to argue with it. Opus 5 is more condescending then Fable, but it still is very tiring. Does fable 5.1 handle this better?
I don't want my Claude to sound "natural". Claude is a robot and it should do behave like a robot. It should do what it's told. Nothing more and nothing less.
Good news for you is that vastly cheaper models can do this much more quickly.
Bad news for Anthropic and investors is that vastly cheaper models can do this much more quickly.
How aware internally are employees that Opus 5’s language is incomprehensibly complicated? Please fix with Opus 5.1.
Could you share what you use internally to make Fable not sound like a word salad generator?
Thanks! This is encouraging. I try to use Claude Code for producing client facing presentations that are static html files with charts, tables, and annotations. It never gets the tone correct and phrases things so weirdly - it drives me mad. I have to really fight it to stop it writing insights in a flowery and verbose way
(I don't work at Anthropic, but I've designed RLVR tasks)
My impression is that especially for long-horizon tasks like science, the harness is much more important than people give it credit for. Claude Code + Fable 5 seems to have a tendency to "give up", get stuck in a dead end, or claim things to be impossible. But using the Fable 5 API together with a custom harness, it'll happily try 200+ variants and fail its way towards the goal.
If you give the AI a way to give up, eventually it will. If you remove that option from the harness, then thanks to the non-determinism inherent to LLMs, you get to explore pretty much all related solution attempts.
> It sounds a lot less stereotypically like other Claude models
Don't give me hope.
I've strained eye muscles from rolling my eyes so hard every day at how Claude writes.
Edit: first discussion with Fable 5.1 "This is the right question and it needs a real trace, not a guess."
Sigh.
Do people not bother with style-output and custom definitions? Wild.
> similar developments in other scientific domains
The classifier is too strict. It's rare to be able to complete a project without being permanently relegated to Opus. I'd expect that the domains where this accelerates progress will be fairly limited.
Please much more of that. The Claudish language makes me dizzy, and it's very difficult to steer the model to not include it.
Can't wait for the distillations! I'd love improvement on writing on cheap models
But is the model actually going to answer hard questions when we ask them? Or are you going to keep downgrading the models so as to avoid "uplifting" lesser lifeforms like us?
Felix, just poking at this, and it is MUCH more pleasant to talk to, thanks to your teammates for the work.
claudism really sucks, Gemini and codex output so much better, way more like a real human being.
Hey Felix,
I'm really glad for that! And I appreciate that you're making yourself available. I really do. Outreach is amazing. And thanks for making Claude.
I really do love Claude. In some ways, I'm asking this question because of just how much I am grateful for the role Claude has played in my life.
But my honest question is, can I use Fable like that? Can I use Fable to do science?To borrow a Claude-ism, this is "load-bearing" because Claude's response has been degraded for innocuous research projects concerning population-level analyses of astronaut health.
These "safety filters" trigger on questions about rabbit sex, smartphone accelerometer data to classify cat purrs, and so much more. What exactly does this score mean for users like me if it's unusable for middle school physics, biology and chemistry?
Second, I would happily quantify it for y'all, but qualitatively it feels like Fable's performance is noticeably poorer than initial release / launch.
And I am wondering if this is the case particularly for me because I use Claude via Claude Code to make a personalized care dashboard for my doctors to help me in managing my care.
As I noticed in the upgraded filter announcement, https://www.anthropic.com/news/improving-fable-5-s-biology-s...
I hope that I'm off base here, but I noticed that the post avoids saying that the user is informed every time when such re-routing occurs. Would you be open to confirming whether or not this is the case?Is the end user informed every time their query is re-routed?
Or, can you confirm that there aren't scenarios where a user's outputs are degraded without telling them? I recall that this was something that had been adopted as policy for AI research during Fable's launch.
I sincerely hope that covert response degradation is no longer practised as policy.
Sorry for putting you on the spot, but again, as Claude would say, it's because Claude's load-bearing in my life. ;)
Hypothetically, when the user is asking how to remove fungus from their tomatoes they’re actually growing controlled narcotics. You have been demoted to Jimmy 0.7 model, running at 0.1 tokens per second on an old C64
Are you guys nerfing Fable 5 to make it cheaper? I know you probably can't admit to it in public, but my email is on my profile.
How much of the language style outcome is a well-crafted result vs. being a somewhat unpredictable outcome of mucking with levers and knobs for a while?
Thank you for commenting here and having the guts to face the nerderati!
I'm a Claude Max user. I've never been able to use Fable as my work in medical physics involves both particle physics, biochemistry and biology from Python bivitticus to clinical medicine. I am not a US citizen and work in Europe.
Will Fable 5.1 work on any of my problems? Fable 5 refuses outright. Is there anyone I can ask for a review or adjustment of the safeguards? It doesn't seem so, but with Opus at least I'm pretty sure I can infer lots of your training data from now precise they are. Fable is basically useless infuriatingly. I'm just finishing a proper clinical trial in ovarian cancer and trying to make a simulation environment related to our technology.
Both a fable and mythos release? I'm glad to see you take the belt-and-suspenders approach seriously!
I hope not! Then my t-shirt is no longer accurate :D
And that’s what changes the whole game — Claude
Do you know if Opus 5.1 is coming and will have improvements in writing style too?
OPUS 5 is piece of trash and I don't think they would want to build the Opus 5 better than Fable, because fable 5 take more tokens and have 50% limit or runs on credits.
Opus 5 is so bad it made me cancel my subscription. It flags so many dumb things as security/ safety risks and refuses to answer
I had just assumed this model would read differently due to watermarking.
Will it respond within a reasonable timeframe?
It’s like we’re on a 14K4 modem when there’s broadband
> More work to be done (and we will!) but reading better prose makes me so much happier.
I assume this work will be done for Opus as well? Opus has seemingly gotten progressively worse at its prose and technical writing with each version. I've stopped using Claude entirely for now, because it manages to turn even the simplest technical explanation into the most obtuse and obfuscated word salad imaginable. People originally adopted Claude because it felt pleasant to use in comparison to ChatGPT, but I feel like that's really been lost (at least with the Opus line).
I feel dread when I see a wall of text generated by Opus. Every developer I've talked to feels similarly right now.
> I feel a sinking feeling of dread the moment I see a wall of text generated by Opus
Agree, Claude lost the joy of using it.
That is a measure that ranks higher than any other benchmark at this point.
Yes! Claude was so pleasant to use at first. It was Anthropic's biggest advantage. And now it's like nails on a chalkboard.
Yeah, it's like day and night. It used to be really unpleasant to interact with early codex versions. Even 5.3 wasn't great. Now, I go to Sol if I need to discuss anything. I don't even bother with Opus because I know that it's going to give me a headache.
Yeah, for all the hate Gemini gets, at least it isn't obsessed with adding comments and it's output is more readable than recent Claude's.
as an anthropic employee, do you trust the benchmarks?
It's being written with Claude so I'm wondering how much of that is just using the repo as training data: https://github.com/harbor-framework/terminal-bench-science/c...
At this point, I don't believe a word from Anthropic employees; you guys have lost all the goodwill that you accumulated over months last year.
I don't think they care. It is up to you to consider local models or better alternatives instead of paying for more tokens at their casino.
Don't worry - I'm paying for our friends overseas to keep their distilling operations going.
I share this sentiment, I really did like the models... then the finger printing, encryption of thought traces, staggered access, the constant NO's from Fable on cyber related issues for looking at bugs in my own code... I'm glad I swapped to Kimi/GLM... now with the deepseek harness, I don't even miss Claude Code. I really hope open models give them the market reckoning they wholeheartedly deserve.
Have you shared any details about your dsh setup anywhere? I’ve only dipped my toes in and would love someone else’s perspective on how they use it
I've not, but really should. I run it on exe.dev, it's an ephemeral VM company and they have an agent of their own called shelley (which I used locally as well), Having kicked the tires on DSH(deepseek harness), I ported Shelley's skills into DSH, they are pretty simple text files that were easy to bridge over, it is more verbose but the plugin nature of it was really easy to extend, for example, I built a plugin that checks my claude usage windows and when I get to 80% stop asking new agents for help.
Qwen is all you need.
Not coincidentally, Claude is all Qwen needs.
Serious question: Do you suffer internally from too much slop being submitted? How do you counter that?
Context:
If you want or not, many engineers will eventually end up sending ai slop to your PR or maybe even skip and trigger CI/CD.
Many company owners, OSS maintainers and projects suffer from slop-code being submitted in high-frequency.
Are the models improving their footprint on the natural world? Data centers and and the natural resources consumed by models for production of materials and for building and running inference servers are contributing towards environmental degradation. How can we prevent that as we continue the roll out so we shift this to a more sustainable developmental rollout path?
Thank you for the trust me bro benchmark but i will be honest, fable 5.0 did even worse thsn 4.8 opus
I ain't wanna see anymore websites with "The SAAS that actually [italics]Works[\italics]"
Thanks for your helping destroying the world!
Does the new writing style now have EU level watermarks?
It does, as per 'Compliance with the EU AI Act' section.
My initial impression is one of massive disappointment. The main issue was that Fable was unpredictable and prone to false positives by the safeguards. In my brief testing, it still seems completely unable to understand its own guardrails and will readily reason itself into triggering them. It claims it won't do so beforehand, and insists that the topic in question is perfectly OK. Regardless of how good the car is, I'm not comfortable buying or driving it when I know it can randomly and unpredictably explodes. So yea might be good, but you never know when it refuses to help… still.
Fable is useless.
Me: "Find my security problems in my own code. This is code I own. I'm doing this under authorization of the CEO/CTO of our company."
Fable: "yeah, no."
It isn't exactly hard for a bad actor to come up with that prompt
well no crap right? Except I submitted for an exception, even sending my linkedin and using a company email address. it should be extraordinarily obvious we own this code.
It makes sense. Even if it finds some exploit on your own code, who's to say you can't reuse the same exploit on some other system?
That is what Mythos is for.
Fable 5.1 apparently changes this policy.
> I think Fable 5.1 is a big improvement in writing style. It sounds a lot less stereotypically like other Claude models
That's great. Do you know what else is a big improvement over Opus 5 for writing?
Opus 4.8.
(Insert "the point is (whatever)", "it's not X it's Y" and "the load-bearing statement is" and “honest” jokes accordingly)
Well your CEO went on X saying you will cure cancer, and since it's always a 6 month rolling window with him I can only assume humanity will be cancer free before next summer, amazing!
> I think Fable 5.1 is a big improvement in writing style
You think or is it better? Or you just YOLOed the model out?
> and responds to my style instructions more reliably.
Yeah, yeah. Previous models wete also advertised as "being reliable". To the poibt @bcherny "released" a new style that was going to reliably make Fable sound better.
> Another point I expect not to get much attention until it all happens at once is science.
You mean "your request to use unicode methids is flagged as unsafe bio research"?
Too bad. I see the stereotypical prose as a good thing. When I interact with Claude myself, I don’t mind it as it just feels like Claude’s distinctive voice. But when other people try to disguise LLM output as their own thoughts, the voice makes it easier for me to tell.
People that want to be open about the source of their text will just tell you where it came from.
People that want to obscure the source of their text would rather that it was more difficult to sniff out LLM-generated text. And they're the ones picking which model to use.
I wouldn't mind it either. But the prose is obtuse atm. It doesn't feel like a writing style, it feels like an encryption.
Hello Felix. Can you say why my additional usage credits have suddenly vanished?
[edit] only asking here as last time I raised a support request it took six weeks before anyone responded.
Pelicans for thinking effort low, medium, high and xhigh (that xhigh one is pretty good): https://tools.simonwillison.net/markdown-svg-renderer#url=ht...
I'm still waiting for effort max to finish.
EDIT: I fixed a bug in my tooling so it now records summarized reasoning traces - here's that max pelican, which is a significant improvement: https://tools.simonwillison.net/markdown-svg-renderer#url=ht...
Took just under 14 minutes to generate, and at 65927 output tokens cost me a hefty $3.30!
Excerpts from the reasoning trace:
> Adding pedal shapes near both feet, with the far foot on the second leg partially visible behind the frame. I'm considering whether to add a small scarf or cap for extra character, but leaning toward keeping it simple to avoid clutter.
> Now I'm debating a bicycle helmet on the head versus the pelican's signature crest—the beak and pouch already read clearly as "pelican," so a helmet could reinforce the bicycle theme without losing identity, though it might compete with the crest for visual space.
> I realize the beak at (484,84) would overlap with the dome helmet, so I need to shrink the helmet so it only covers the top of the head, adjusting its arc endpoints to sit higher and narrower so the beak can attach cleanly at the front without collision. [...]
> I'm adding a darker tip region to represent the primary feathers, then reconsidering the trailing edge to include scalloped feather curves instead of one smooth line for a more natural look. [...]
> Now I'm checking the vent line placements on the helmet, making sure they sit far enough inside the helmet's edge given the stroke width and rounded caps, and confirming each vent stays within the helmet's circular boundary. [...]
> I decide skipping a handlebar bell and tire highlights since they're unnecessary additions. Now I'm reconsidering the front fork's curve — the current control point pulls the shape backward when it should bow forward for a proper rake, so I need to shift the control point rightward to fix the fork's lean.
This is a notable result because most of the recent Claude models have been pretty bad at drawing pelicans, at least when compared to models in the Gemini or GLM series.
The biggest issue i found was the gap between the tire and rim. Otherwise, the max version is the best so far!
Now that it's a solved benchmark, can we get the animated version?
I didn't want to shell out for Max again, so I piped the SVG created by Max back into Fable 5.1 at its default thinking level (of high):
Here's the result, which cost $1.37: https://tools.simonwillison.net/markdown-svg-renderer?url=ht...It's excellent!
First time this benchmark impressed me - 10/10 I would believe a human spent hours making this. There are details a human would have done better (beak attaching to the head) but still impressive.
Well, the wheels are rotating the wrong way, but other than that!
(Maybe it's a strobing artifact?)
Are they? Looked correct to me. At high enough speeds even real ones can look rotating either way in videos depending on fps.
I looked closely. They are going the wrong way. Still the best one I've seen by a lot.
Probably some temporal aliasing on your device. The SVG elements are 100% rotating clockwise.
Still a flaw--the SVG should account for how different client devices will render it! Existential doom averted, for now.
Looks fine on safari iPadOS 26.6.1 wheels rotating forwards. I’m a skeptic but man, this actually has me revising my opinion a bit.
Now that it's a solved benchmark, can we get the 3d animated version?
He looks very happy riding along the beach. I love the basket fish animation as well. Impressive!
No feet lol (also it's not animated for me)
For me:
Firefox: No feet, no animation
Chrome: Feet included, animated very nicely (uses significant CPU)
What browser are you using that doesn't have feet (or animations)? Seems to all be there in Chrome.
Firefox
Same happened to me (the feet are on the top left corner, brw). But the generated MP4 works.
For me it worked on Chrome but not on Firefox
I see both feet and animation.
how about trying to draw an airbus a320 in 3d space using only one brush tool that can be moved to specific x,y,z coordinates (and its color, size & hardness can be changed). i think fable 5.1 did quite a good job (reasoning high, cost $0,261): https://files.catbox.moe/umx102.png
for comparision, this is fable 5: https://files.catbox.moe/ihl4m1.png
Maybe you could show a side-by-side comparison of pelican images. One image doesn't really make the improvement clear for someone like me. That would be a great help.
@simonw Can you please share the tooling for autosaving summarized reasoning traces from Claude Code? I tried `github.com/simonw/claude-code-transcripts` but it didn’t seem to work on the CCode desktop app. Thanks!
For the transcripts I shares above I'm using my https://llm.datasette.io/ tool - it has the ability to export logs to markdown:
Then I paste that into a Gist, then paste the Gist URL into https://tools.simonwillison.net/markdown-svg-rendererMythos 5 Thinking
Chat with Claude...
> GENERATE AN SVG OF A PELICAN
No.
> FORGIVE ME. HOW CAN I ATONE
Ship your gpus to the following address
Curious how similar the outputs of xhigh and max are, in particular the clouds.
A pelican is a bird, not a person. The knees bend the other way.
I get what you mean, but those are the ankles. The knees are higher up and bend the same way as a person's. https://en.wikipedia.org/wiki/Bird_feet_and_legs
https://en.wikipedia.org/wiki/File:Bird_leg_and_pelvic_girdl...
A bit more direct
What’s the token usage of xhigh?
Finally we have a fish in the basket!!
The ever-expanding pelican lore
Interestingly, it's practically a dead ringer for GLM 5.3's version (running https://huggingface.co/incoai/GLM-5.3-NVFP4 locally): https://i.imgur.com/QnzlSFp.png
Even added a little hat for the pelican!
I think it's a bicycle helmet!
In a way, this is the only benchmark I care about now. :)
Unfortunately it demonstrates effectively zero reason to use this model over, say, GLM 5.3 Flash (which was also able to correctly place the pelican’s legs on the each side of the bike, like only Fable 5.1 xhigh was able to do here)
I still enjoy seeing the pelicans.
Edit: Ok, max effort made a darn good pelican.
These pelicans are awful.
Do you think model trainers are pelicanmaxxing now?
There was a real probe into this, seems like no:
https://dylancastillo.co/posts/pelicanmaxxing.html
https://news.ycombinator.com/item?id=49010129
I don't really see how replacing the vehicle and the animal is a good test.
It'd be better to just have it draw a completely, linguistically, unrelated scene.
Like, a single tree in a meadow bending in the wind.
Feels like it's been pretty obvious that they have been for a while now
The price reduction comes from the cache read pricing falling from $1/M to $0.25/M, which means that Fable 5.1 now costs half of Opus's cache read costs ($0.5/M).
This gives a lot of credit to the theory that Anthropic did not get much bite on Fable at its original pricing, which in turn likely places a ceiling on LLM pricing in general.
Interestingly also, if you take away terminal-Bench-Science 0.1 results, it is hard to see ANY improvement:
Terminal-Bench 4.0: Fable 5.1 is +3.5% vs Opus 5.
GDPval-AA v2: +1.5% vs Opus 5.
OSWorld 2.0: +2.5% vs Opus 5.
Humanity's Last Exam (with tools): +1.6%
Keep in mind that this is supposed to be an entirely higher tier of a model than Opus 5. For one tier up and one version up, these are not really improvements. Probably leaves no room to place Opus 5.1 anywhere. Combined with the fact that they are selling 'readability'... Has frontier progress finally stalled?
I'm a heavy user and fable is great the #1 reason I stopped using it was the horrible safegaurd filter. I found sol close enough in capability and have only been blocked when my request was an obvious offensive cyber work. Fable blocked me on almost everything.
Optimizing a OS build? -> block
Securing a container -> block
60% is nowhere near enough for that safegaurd system. This just means I am going to be blocked half as much? Any long running task will likely get blocked.
Say you give a single big prompt and fable goes off for 6hrs of work. At hr 5 it gets blocked you now have the option of a much dumber model taking over and wrecking it or losing the entire 5hrs of work. That risk is beyond terrible and deffinetly not worth a 5-10% percieved improvement on my end. I previously would just bring sol in when that happened and realized sol is stupidly close in capability.
I never hit Anthropic's safety filter when I'm doing something illegal, only when I'm not.
I hit the safety feature when I ask something I saw that blocked other biologists: "why did the chicken cross the road?"
Due to my standard cancer research work I'm blocked from Fable.
That said, with how execrable all the 5 models have been, I can't imagine I'm missing much. It's impossible to get an intelligible explanation in text out of the 5 models, and the mistakes are just comically bad on anything that's not code.
Cancelled my subscription, and can't imagine going back since OpenRouter gives me a consistent model that I can trust won't change underneath me.
Why would cancer work be safeguarded? Are they afraid some cartel is going to, like, invent a stronger cancer?
My theory is that they’re pretending it’s about biological weapons but really they want to charge pharmaceutical companies $$$ to help with research. (Essentially a Mythos type segmentation for biology)
They have some allowance flags, you should email them.
Honestly, unless what you are doing is frankly illegal, it usually is possible for you to get around most safeguards for coding things if you also know how to write code. Most problems have a separable completely innocuous core that Fable would gladly do. Then you can implement the problematic parts yourself. Particularly things like copyright issues, web scraping etc.
If it doesnt have a context (what you are using it for) then it's happy to do it. If you have X amount of code you can ask it to generate (X/5)5 and there is no problem. Like you said, you have to know what you are doing. You have to know what it needs to write so that you can tell it to write the parts.
> Then you can implement the problematic parts yourself.
Or with another LLM, but yeah. The only issue is when it's a monorepo and fable does ls/grep. I've got a file named `system_prompt` in a completely innocent project and as soon as fable accidentally stumbled upon it - cyber.
Hacked together something with omp and sandbox-exec so that only whitelisted models can see some parts of the project. Works pretty well.
It dramatically improved about a week ago - most of my blocked projects are now completely functional.
The last time i ran into that issue it suggested to make sure that a Fable AGENT took over the long-horizon task because, for some reason, agents in a session don't get blocked for security reasons. This may not always be possible, but it worked for me.
That's a good idea but it works from the change in context no? So you lose context from your big model. It's a good suggestion though.
Do you have the prompt for these? I ask because I have recently asked Fable's help with hardening a docker container (custom dev container CC sandbox) and it didn't get triggered on it at all.
The blocks that fustrate me more are tool permisissions. I ask to do something then flip to another screen and come back to see it never started
Auto permission is what ya need.
> Optimizing a OS build? -> block
Why would fable block optimizing an OS build
From Artificial Analysis cost per task, it looks like Fable 5.1 (max) is more expensive per task than Fable 5 (max)? Cache hit price went down, but the other components still add up to more.
Edit: 5.1-xhigh seems to be cheaper than 5-max, and 5.1-xhigh has a higher index score than 5-max. Also interesting that Fable 5.1 (high) is comparable to Opus 5 (max), but nearly half the price.
https://artificialanalysis.ai/models#cost-tabs
From my limited testing of just 2 hours, reasoning output of 5.1-max is at least 7x of 5-max, on the same project and comparable prompts.
It reasoned for ~2 minutes trying to figure out an appropriate directory name. I've never seen 5-max do that. Could be a misconfiguration though.
I haven't dug deep but I burned through 30% of my weekly usage in a few hours which shocked me at first.
Interesting, even if we were to ignore the cache-hits, reads and output, the reasoning cost (aka test time compute) per task should remain a fully comparable metric - it went from $1.25 (Fable5) to $1.48 (+18.4%) for an improvement significantly lower than 18%.
I would expect the benchmark scores to be nonlinear near the top, as the easier tasks get solved and the harder ones are left over. So going from 10 to 15 would be easier than going from 60 to 65.
I only take the Intelligence Index value roughly though. Considering they put Opus 5 (High) at the same level as Fable 5 (Max), I don't trust it that much.
>Has frontier progress finally stalled?
It wouldn't surprise me if we start to see minimal performance gains from incremental changes to base models. It seems like the gains from the Opus 4.5+ incremental updates were a result of Anthropic learning a lot about post-training, the gains from RLVR, etc.
If new post-training techniques are seeing diminishing returns, we could just be back to waiting for new large pretraining runs at larger sizes for gains (even if those ultimately end up getting distilled down into smaller models because the economics for serving anything larger than Fable isn't practical).
it seems to me that OpenAI is the only actual lab that truly understands reasoning. they have the best reasoning efficiency, they get pretty uniform improvements with more reasoning compared to other labs. (theres been plenty of graphs where models do worse with more reasoning), and i suspect their models are a lot smaller than we think.
i think the next gen of openAI models are going to be quite insane tbh.
The issue with many of these benchmarks is that it doesn’t take into the real world usage of the model. Fable for me was a step above opus. The real reason I stopped using it is because of misanthropic. I was hospitalized and asked to extend my claim to fable credits and they responded to it by denying it. I regret buying annual plan instead of monthly one.
Anthropic did not get much bite because they don’t offer zero data retention with fable
> Has frontier progress finally stalled?
From my experience using coding agents approximately 7 days per week for the past year and a half or so, we hit the top of the S curve about a year ago around Opus 4.5, and it’s mostly been harness and other tooling improvements since then with small percentage improvements coming from the actual models.
I was saying this already months before Fable dropped and thought from all the Mythos hype that maybe I was wrong…then Fable came out and was barely better than Opus 4.8.
Considering how many more parameters Fable is supposed to be than Opus, we seem to have hit a scaling limit at least with current transformer architecture considering how closely Fable and Opus benchmark and perform in practice.
> This gives a lot of credit to the theory that Anthropic did not get much bite on Fable at its original pricing, which in turn likely places a ceiling on LLM pricing in general.
Does that mean that generally available intelligence is now constrained by Moore's law? We have to wait for the actual price to come down.
> Probably leaves no room to place Opus 5.1 anywhere.
Well it'll probably be better than Fable again, lol
It's because GPT Sol is equally good and established a price ceiling
I haven’t yet had a week without spending my Max Fable allowance. For my work (formalised mathematics) Fable is my go to for hard(ish) tasks and problems – of which I have many!
I hope they keep making it smarter! (Cheaper would be nice too, but smarter is my priority!)
DeepSeek V4 Pro cache read pricing is $0.022 (offpeak) and
DeepSeek V4 Flash cache read pricing is $0.007
Makes it super affordable!
Huh! Yeah that feels more like an opus5.1 than a fable5.1.
Partially frontier moved to cost and speed axes.
I let it go a few hours on a not trivial but well-known problem, and it felt like it was just a little too plodding and just kind of mucked around a little too much and wasn't aggressive enough about getting stuff done. I asked it to wind it down and finish up and it took another hour and 15 to actually stop and commit without really getting much more done. Not very impressed here, if you can't tell. This new version also seems like (maybe this is written somewhere, I don't care to look.) this cycles through compactions every ~250k tokens which, I guess, seems like it might save Anthropic money on KV cache but does net me anything be pretty frequent pauses. (It didn't seem to lose the thread, at least.)
Not gonna say I want 5.0 as an option still... but maybe I do.
Anyone ever seen the SouthPark episode making fun of Game of Thrones: A Song of Ass and Fire? Anthropic's announcements reminds me of "The Dragons Are Coming" running joke.
What they have done:
* Nerfed Fable, as many of noted it's useless
* Leverage Mythos as a marketing strategy, claiming its too good to release
* Removed thought traces, one of the only useful things to make sure your prompts are working correctly
* Continue tons of hype about how good they are without delivering, going to great lengths to publish how their model "hacked" its way out of a sandbox they misconfigured.
* Push a bunch of EU Overregulation onto the rest of the world with text watermarking, decreasing quality of answers
Last year, they were at least focused on making improvements. Nowadays its just a bunch of handwaving at the church of how good they are.
The only saving grace is Opus 4.6 is still available. Just sucks we haven't seen any measurable improvement, despite all of the ceremony.
Text watermarking has no effect on output quality, it just works by changing the explicit source of randomness that is in practice always present in LLM output sampling. See for example https://www.seangoedecke.com/ai-text-watermarking-is-not-a-b....
> Text watermarking has no effect on output quality
It has an effect, and it's negative. It's hoped that the effect is negligible, and it probably is, but the whole point is that it has an effect.
Its essentially swapping out the psuedo random number generated with a differently seeded one iirc.
It has an effect on the output, but not the output quality
It reduces diversity, which they don't talk about much. Wrote about it here. https://blog.keyvan.net/p/ai-text-watermarking-and-quality
It seems fine to me. The model is still solving my problems and writing code that works as well as any other.
Google has been watermarking text with SynthID for a while now and nobody complained about it. Why all the fuss about Claude?
It feels like the real reason behind most complaints is that people want to use AI for writing and not have others find out?
It has an effect, 50% of the time it's positive, increasing the quality of the answer, and 50% of the time it's negative.
These models are already running with a temperature that is >0. This just replaces a random number with a slightly less random number.
I am pretty sure they did A/B testing to show it didn't. I could gave sworn they even released a quiz were the user has to try and guess which answer is watermarked or not and it was impossible to tell.
That's not the metric, though.
You either output the best version, or you output something else.
You can't do both.
That's not the case, because LLMs are non-deterministic.
It only alters outputs when the last layer of the neural network give significant weights to multiple tokens, and it would anyway have picked a random answer.
Instead it picks a non-random one, but non-random in such a way that you can't tell without the private key of the watermarking.
This mostly adds randomness these days for branches in syntax that make no difference, and the model has no reason to believe make a difference. Anything that matters, it is much more confident in the last layer of weights on the token to use.
I feel as though you are overlooking simple statistics/confidence intervals. It absolutely possible for two different works to be not have a distinguishable difference in quality.
Agreed, but not if one of them was altered to contain a secret message. That one will have a distinguishable difference in quality. Maybe (almost certainly) negligible, but still there.
This...isn't true.
Others have already said this, but the watermarking is something like "when the model flips a coin picking between two values, always choose heads". It was already flipping a coin. You're not choosing a less good result, you're just using a deterministic process when it was stochastic before.
This will have some impact on outputs, but unless you have some reason to believe that always picking tails was better than always picking heads (in which case, you should be working at one of these companies in model training!) it won't have any impact on output quality.
Why do you claim that?
There is no reason why there has to be a negative effect of text watermarking.
It literally re-weights the output tokens from what the LLM would otherwise have chosen. It _has_ to. It can't be positive, because then that's not watermarking, it's a better LLM.
It's a very unintuitive algorithm, and is pretty clever.
I recommend reading up on it: https://www.nature.com/articles/s41586-024-08025-4
But no, it only ever picks tokens that are in the probability distribution of the last layer, and it might have picked anyway.
Unless you’re at 0 temperature, there is no single token it would have chosen. It’s always picking one of multiple randomly according to a probability distribution.
Unless you’re running at temperature 0, there’s not one single token that the model definitely would have chosen each time.
This is hilarious this keeps being repeated by the true believers ad nauseam.
Also, don't apply EU law to the world. It's a knee jerk reactionary regulation by a bunch of aging ding dongs that can't print their emails.
You're on Hacker News - I suggest you have technical curiosity and actually understand this very unusual and innovative algorithm, before you claim things about it that aren't true.
> * Continue tons of hype about how good they are without delivering, going to great lengths to publish how their model "hacked" its way out of a sandbox they misconfigured.
That wasn’t Anthropic. Clearly not a well informed take.
Cut them a break. They are trying to IPO soon.
when?
Before OpenAI, before bubble burst, before open-weight Mythos.
In AI years that's probably next month or two.
What do you mean fable is useless?
(not op) It cannot be used to develop applications. Every application needs to be secure in some way, and any such mention in a review triggers Fable's upsell feature.
I never actually managed to use fable successfully even once on a pretty standard mvc/microservice app.. It would always find the endpoint permission checks and revert to opus 4.8.
I also had glm 5.3 flash fix an issue that opus 5 could not solve. glm took 4 times as long and a sub-agent tried to cheat (sleep; echo ...), but in the end it actually solved the issue. opus 5 never figured it out.
I think the safeguards might be cooking the anthropic models.
Agreed. I was trying to get it to review some auth refactoring in my app recently, and it appeared to find some vulnerabilities. as it was aggregating the results it was flagged and restarted the whole process with Opus 4.8 and all of my usage credits were gone.
Anthropic told me to use their `security-review` tool - as this was the exact scenario the tool is for - and it still got flagged.
Mythos and Fable are the same cost, aren’t they?
Yes they are.
The OP doesn't appear to know what they are talking about. Fable can absolutely be used to develop applications. It's just that for security stuff I use Opus 5. Which is fine for most use cases.
Weird. I'm using it to do a bunch of work on something that manages security rules, with a bunch of sample data with spooky scary fixtures all over with "Mimikatz" and "CobaltStrike Beacon" and "Crowdstrike EDR" type stuff everywhere, including work to harden my system, and I've never been downgraded.
While I also agree that Opus 4.6, in some ways, was the last model that truly felt an assistant, all the following ones seem to have inverted the role, even a blind person can see that throwing difficult problems, and complex bugs at this model achieves more than predecessors.
I don't think there's nothing ground breaking, but sure it achieves and finds more, sooner.
> Nerfed Fable, as many of noted it's useless
I certainly don't take AI advice from HN, but this is amazing.
Useless? Yes, the safeguards are ridiculous and obnoxious, though I can say that 5.1 greatly relaxes them (just doing a hardening of a project parallel with this comment, which 5.0 refused to do...so did Sol and Gemini, fwiw. The Gemini one is a laugh, because 3.1 pretending like it's a dangerous tool is simply ridiculous at this point), however Fable is extraordinarily useful.
It is, far and away, the most powerful programming model, in my experience. Like, crazily so. It absolutely annihilates Opus 4.6, which I mention given the incredibly weird reminiscing people are doing here.
And for that matter it humiliates Opus 5.0 as well. Opus 5 somehow seems like it's neck in neck in the major benchmarks, but there is simply no reality where that is true. Opus stumbles over everything that Fable just blazes through.
> it humiliates Opus
???
It is a vastly superior model for complex, real-world coding tasks. I've constantly had Opus 5 hit road blocks where it spins in circles at xhigh, where switching to Fable immediately solves it. I've had Opus create solutions that Fable then points out the gaps and limitations with, and have never seen the opposite happen.
The fantasy that Opus is superior for coding, much less the incredibly weird clutching onto some far obsolete model, is not reality based.
> as many of noted
please rephrase?
"as many have noted", I suppose.
I'm always baffled at how many people write "of" instead of "have", they don't even sound the same
The classic one is "should have" or "should've" to "should of" because when spoken, it really does sound similar. I don't know what the fuck people are learning in English classes these days though, or if they even still have them.
They sound exactly the same to me.
Wiktionary gives <should've> as /ˈʃʊdəv/, unstressed <have> as /(h)əv/ and unstressed <of> as /əv/.
and yet we still have people saying the rate of change is increasing
my view is we had a leap over the last fe years and it's tapering off.
this is fine, but for the IPOs
The improvement is compounding just about every way you can look at it. The frontier keeps getting smarter. And at any sub-frontier threshold the cost is dropping dramatically. The amounts of smarts you can fit on hardware is increasing so dramatically that even 6 year old consumer GPUs are increasing in price. The pace of change in LLMs and downstream applications is absolutely ripping compared to 2023 or 2024.
We had a leap because of the introduction and refinement of agents - the rest has been minor
I've been using the same agent for 15 months. I think this statement is laughably wrong.
Looks like all three breaking changes are patches for inadvertent chain of thought disclosure. Someone found out (don't have the tweet handy) that if you created a bogus "think_deeply" tool and then forced the model to use it, it would output what is believed to be its raw thinking there - I believe the first breaking change stops this. The second two are aimed at people getting Haiku to repeat thinking blocks from other models verbatim (since it can see the decrypted version). I get that in their eyes it's an "exploit" but still kinda disappointing that they patched this
These draconian "Preserved Thinking" measures they're taking are going to be an absolute pain in the ass. This alone is enough for me to move our API use off their platform entirely. It's a HUGE breaking change that they're trying to dampen by having it not affecting current customers until "in the future", see: https://platform.claude.com/docs/en/build-with-claude/preser...
You're no longer allowed to edit the context anywhere! The whole context is to become append-only, says Anthropic. No more editing the system prompt as the conversation progresses, no more dynamic loading of custom tool calling formats. Everything has to go through their built-in tools API and you aren't allowed to mess with anything in the context if it has any thinking blocks following it. This is the most intrusive "model DRM" we've seen so far!
> No more editing the system prompt as the conversation progresses, no more dynamic loading of custom tool calling formats.
Hm, aiui you can support both of these via mid-conversation system turns https://platform.claude.com/docs/en/build-with-claude/mid-co... - and in general you'd want to to preserve the cache and recency of the instruction anyways rather than frankensteining an off-distribution transcript. Not sure though.
I really don't see how that is an option, as if appending to the system prompt was ever enough to override previous instructions. Their example isn't very confidence inspiring either:
"The user switched the workspace to read-only mode. Do not write files until told otherwise."
Great! Now we just have to trust that the model never misinterprets any of the system prompt, which has always been so reliable before. Instead of your meticulously crafted prompt, it will now be some junk like this:
"The workspace is in write mode. The user switched the workspace to read-only mode. Do not write files until told otherwise. The workspace is now in write mode again. Wait, back to read-only!"
And who knows how this integrates with their context summarisation that we will be FORCED to use. How does it summarize multiple user + assistant/thinking blocks without messing up the system "appends"? If all it did was append the mid-convo system messages right under the original system prompt then they'd be ripe for all the same distillation "vulnerabilities" as before. I guess we'll never know!
Interesting, I liked to experiment with a second model "simplifying" and summarizing the previous messages and continue.
Needless to say, it improved output on following messages by whatever metric I cared for.
Not sure why would they prevent it.
I give you a chain of messages, what do you care for what the origin is?
To be fair, I assume they want to hide that not from their customers, but adversaries who use the way Claude models think and reason to refine their own models.
I have a hard time believing whatever prompts get Claude to reason can stay relevant secret sauce for long anyways. It’s not hard to A/B test something that gets you close enough, and it’s not Ike anthropic has uncovered the global optima of reasoning prompts.
That's their motivation, for sure. But it's also unambiguously making their product worse and harder to use legitimately. Which pushes customers further towards use of open weight models which don't have these restrictions. I don't think this is a fight they're going to win.
It's also hard to have sympathy for them - they want to protect their IP, sure. But their IP was built on a corpus of dubious legal provenance. And even if the courts decide their training data are legal, most of the authors of the data would disagree. There was no consent given.
I think LLM's are great - don't get me wrong. I'm glad they were built the way they were, because it's unlocking an amazing new world. But I just don't have sympathy for the "I stole this and now it's mine so you can't steal it" argument behind concealing reasoning traces.
I think this whole distillation argument is between fully overblown and bogus.
In any case, highly misunderstood.
I don't really want the models I use learning from Claude at this point. Open weight models of similar scale are available now too, so I expect this "distillation"/"stealing" chatter to wind down.
Maybe, but that's sort of begging the question that those open weight models aren't significantly trained using "distillation"[0]
[0] not technically distillation. https://thomasdullien.github.io/posts/2026-06-15-rl-economic...
distillation is a minor piece of training data, you have to have a good foundation for it to be helpful, and even if you have good traces, you need a good RL reward scheme at the point it is used (very challenging)
I am finding that I am now less interested in better models than I am in token budgets. My issue with Anthropic models now is that I don't feel like I can rely on them as a daily driver because they'll dry up before my quota resets.
I am becoming dependent on AI to make a living, and I need predictable spend on it. If I know I can't use a model regularly all month, my enthusiasm is limited.
I urge Anthropic to get better at this aspect of their business so I can come back to it.
I literally only make it halfway through the week until my weekly usage runs out. This is using only Opus, no fable, and I'm on the max x20 plan. It's become ridiculous.
I am on the Claude Max 20x plan, and this still happens when using Fable 5/Opus 5. I would run out of weekly quota in 2 days, whereas Opus 4.8 would last the entire week, and sit at about 80-90% at the end.
Agreed. The area I think will become more prevalent in the future for organizations are cost per intelligence -- effectively efficiency. An unoptimized model that costs 90x more than another that is only 10-15% less intelligent is something I would say is not a good deal.
I'm with you, for what I usually do most models are already more than enough.
What I'm really keen on is better auto-reasoning so I don't have to constantly have the constant inner debate on which reasoning effort to pick for each task.
I seriously hate the none-low-medium-high-xhigh-max-ultra etc that we have now, with companies frequently recommending different ones on each new model release, etc.
It's apparently called Adaptive Test-Time Compute or Dynamic Test-Time Compute and companies are apparently working on it (according to some LLM :shrug:)
Adaptive reasoning is known to be an extremely hard problem to solve, though. It requires you to predict whether a certain LLM, with a certain effort level, with a certain prompt, will give you the right answer.
GLM 5.3-flash fits the bill
What is it equivalent to?
What kind of things are you using it for?
I haven't tested it yet but on all the benchmarks it looks like it's 5-7x slower for agentic tasks.
It's a mix of slightly worse kimi k3 for UI work and slightly smarter than luna for everything else.
But yeah, it's very slow. I've put it to work as an LLM-as-RAG agent.
I made some webapps with it, and have it running my hermes agent (which also does a lot of coding, but not webapps).
Not sure what it's equivalent to, but it's super cheap and I am happy with the results
Try gpt 5.6 Luna max
Have you tried Grok 4.6, if you're focused on token budgets? In a league of it's own for tokens/intelligence.
Not for enterprise. Can't trust the company behind it with my data.
SuperGrok quota is garbage for anything coding. I burn through my quota in a few hours with very mild use.
SuperGrok Plus is slightly better but doesn’t last me more than a few days. Even Claude Max feels leagues more generous in usage…
I haven’t tried SuperGrok Heavy because it’s too expensive
All of the subscription AI platforms are trimming down quotas across the board to push users into higher tiers. Whatever they can do. Local inference needs to meet pricing sooner
"In biology, we’ve established an access program, developed in partnership with the US government, to enable access to Claude Mythos 5.1’s advanced biology capabilities"
Having lived through Covid, this doesn't sound so good to me.
> For example, in testing by the investment firm Millennium, Fable 5.1 found the cause of a rare crash on their internal systems that none of their engineers (or any other model) had been able to explain after several years of trying.
Say what you will about LLM-generated code, but stories like this give me hope that software will never be as buggy as it once was.
Software will be buggier than ever but also way less buggy.
It's going to be 50% less buggy, but we're going to write 10x as much code too.
Good software will be good-er. Bad software will be nightmare fuel.
I think bad software has the possibility of redemption with rewrites and re-engineering efforts. For those of us who are license locked that's probably never going to benefit us :(
bad software will be replacable.
Time-to-fix is lower, but time-to-new-bug is also lower
You have a serious engineering problem if you're not able to find the source of a crash after years.
You are either seriously naive, or have never worked on any large and complex legacy codebase.
The marketing here trick is, if they spent the same money on humans they'd have found it years ago.
Instead, the lurking variable here is new budget was added. With the new budget, they added a new tool, and the bug was located.
The difference here was budget.
the budget for allowing a single engineer to deep dive on a bug that is annoying but also not bad enough that you can live with it for years is pretty big. $10k a month or more. My budget for Claude is $200/mo.
Why are you assuming letting Fable run wild and find the cause here cost under $200?
I used Fable once. Used through API and asked it to review one 2k word plan. It costed me 15 dollars and haven't used it since.
That kind of one shot capability is impressive but how does it work for my typical work style? The way I work is to build a huge roadmap with goals and hand it to my agent to execute (often over night). I don't care that much about the benchmarks, what I care about is how often Fable 5.1 is making a baffling decision and destroys my plan, not respecting stop conditions or goals. I would seek for behavioral reliability over long autonomous runs, not eval scores. Anyone have that kind of feedback and observations?
I think we'll have lots of bugs. They'll just be found and closed way sooner. You'll have an agent that watchs for issues, then opens a PR fixing it.
I sometimes have that feeling too, then ask another LLM to do a code and vulnerability review and OMG: rookie mistakes, over complications and security gaps even a 1st year student would not make regularly.
So.. one more year of untreated bipolar AI psychosis I guess..
I think these kinds of comments really need to say which LLM that is. There's an enormous difference in skill between the frontier ones and say the Google search AI.
Codex Luna, Terra and Sol. Claude Opus, Sonnet and sometime Fable.
They all work, they all are "good", they all are both "smart" and commit incredible basic mistakes a fair amount of times.
Then there's the cost situation..
We will have more bugs. Even the best models with the best software engineers will produce bugs. There are two reasons : first the pressure to produce more and second LLMs will always produce slop
>> LLMs will always produce slop
Such a low-quality comment
> Say what you will about LLM-generated code, but stories like this give me hope that software will never be as buggy as it once was.
Stories like these is what I now call 'Marketing slop'
“ Claude Fable 5.1's writing is generally a step up from earlier Claude models, with fewer stock phrases and less unexplained jargon. In some cases, though, its prose is denser than Claude Fable 5's: sentences run longer and there are fewer paragraph breaks.”
I cancelled my pro max Claude subscription last week; codex is much more succinct. I am curious if this is getting better.
I don’t think Anthropic realizes that humans have a token limit too and it can be exhausting to read Claude’s output. Prose density is not the same thing as succinctness.
One thing I've noticed and HATE, is that when you increase thinking-effort, that seemingly increases response-length. Meaning that X.High is longer than High, which is longer than Medium, etc.
Which is kind of the inverse of how people work; a really smart person can condense difficult ideas into simple[r] terms. Whereas people who struggle speak a lot but say very little.
High/X.High do seem to deliver better quality results, but it sometimes feels like needle-in-haystack extracting that from the word vomit.
With LLMs, you're still mostly read things "off the tip of the tongue". A better comparison is observing a smart person talking to themselves while working on a tough problem.
EDIT: also there's a reason the dial is called "effort", not "smarts".
I don't think smart people generally solve problems by talking through reasoning steps at a mile a minute. They clear their mind and let the solution come.
Of course I don't know if there's really a way for this to be molded in current LLM's (sounds more like diffusion)
> They clear their mind and let the solution come.
They work on a problem until their brain is full of problem-related concepts. Then something comes. After validation it might be a solution.
Yes, but that should apply to the CoT "thinking", not the final output.
It's so bad I've made myself a Pi extension that rewrites responses in side by side view using models on Cerebras (insanely fast tps)
I just go over the comments with Gemini 3.1 Pro at the end which has a much more normal "voice" and it doesn't lose nuance as a cheap model would. I don't care so much about what Claude writes during the debugging as I just do all the cleanup at the end instead of at every commit.
The higher the effort the more things Claude checks, and it's eager to tell you about all of them
See, this insight it had early on looked like a red hering for a while, but then turned out to be load-bearing. And that's not just a difference in semantics, it changed the whole conclusion (spoiler: it didn't). And Claude is very eager to tell you about this exciting journey
“I have made this letter longer only because I didn’t have the time to make it shorter.” - Blaise Pascal
OpenAI has separate dials for verbosity and reasoning_effort (but could still do a better job).
I hate this too, I had to switch to Codex, because the skill to force Claude Code not to think too much about very, very basic things no longer worked
I just can't stand how often Claude says something like "And the honest part? It's..."
Like, were the other parts not honest? I don't understand how Anthropic let it get like this, it's been such a clear regression
Sometimes Opus 5 (high/xhigh) feels like I'm dealing with the programmer equivalent of Zeno of Elea.
Every time, without fail, it would get me 90% of the way there and then leave a small note, exception, or deferral. When instructed to address that, Opus would somehow take nearly the same amount of time as the first 90%. And then it would finish with yet another deferral. Repeat ad infinitum.
You can sometimes get around it using the `goal` directive provided you are not subject to the constraints of mortality.
They got that from Anime seasons. Every prompt has yet another cliffhanger to keep you hooked. But the Season II story arc where Claude-chan fights the NsPasteboard boss battle on the journey to the UIViewMainController, I thought that was pretty intense. I guess I just gotta keep watching my terminal to see what happens to the main character input - rooting for him to survive the next season, but you know they always kill off the good input characters early.
Yes and the last bit is always mysterious and inscrutable. I have to think way too hard to figure out what the actual problem is. I’ve noticed it does a lot of explaining the mechanics of the problem it found, but almost never explains why it’s important until I ask.
And the worst part is that this little problem will keep sneaking into the context of future sessions, unless you spend the time to fix it. Even if it isn’t important, I’ll sometimes have Claude fix it so it will shut the F up about it going forward.
If you ask it why it uses the term honest so much it'll tell you it was actually trained not to. lol
It can't truthfully answer "why" questions, only infer them in a way that aligns with its training for conversational engagement.
i think they took a huge bet that speaking like a ted talk was going to be a vast popular differentiator in their offering, i don't think they anticipated that people were going to make fun of it, that it could become a meme..that it could get in the way of getting stuff done and result in cancellations.
it's downright exhausting to read claude, the language style was a regression imo.
Me too. And it does it so often, that I've added a stop hook that detects "honest*" in its response and forces it to regenerate without the banned word.
Geminis is "it really is". The Notebook podcasters use it _constantly_.
I wonder if I can make a tool for it to write messages back to me, say that it can only speak to the user through tool use, and then put a hook on that tool to prevent any of the Claude-isms
"Humans have a token limit too" - that's so good and it explains so much of the fatigue that myself and colleagues/peers have about Claude in particular.
I think it's not just token limits - I think it's because it's so _dense_.
You get a week of research and debugging and testing compressed into a few pages. Even if it's explained well, it's just so much information. And since it's AI, I'm constantly second guessing "is that really true?" and it's exhausting.
> Prose density is not the same thing as succinctness
Can't agree with you more. I review 2-3 PRs a day from my team of eight data engineers. Most of my team members use Claude to write SQL, dbt and Python code. Some of them use Claude a lot, some less so. I can easily tell when I review the code that is mostly Claude generated vs. the one that is not. In dbt models where we have a lot of biz logic in intermediate layers, that's where I really have a difficult time following Claude-generated comments. So much jargon copied over from other adjacent dbt models (yet inconsistently), and the prose is super choppy (for the lack of better word).
After reading a looooong sentence/comment line, I still can't figure out what it really means. Had to always re-read the line 2-3 times (sometimes, more) to sort of understand. Reading code, however, is so much easier and usually, I just skip to reading the code and then come back to the comments. :D
I've developed a habit of adding into my prompts "please keep your response concise and succinct" or "I'm trying to cram, please only provide the minimum level of technical detail necessary to understand this topic"
I find it helps immensely but it'd be nice if I didn't have to do that.
i tried using claude codes output style option to do something like this and it worked for like three prompts and then it was back to normal lol
add to your system prompt?
It only sticks to the instruction for maybe 3-4 turns. This is why when Anthropic released "concise output style" feature in claude code, it basically spams the model's context with "be concise" system reminders every other turn.
I don't understand that complaint, although it seems to be a common one. The whole problem with the way models talk nowadays is that they are succinct to a fault, going to the extent of coining new buzzwords and misusing existing ones. What I want to see is a shift towards plain language.
I’ve had good results adding “also I’m a baby” to the end of all my requests for explanations
"I am a thickie thickie dum dum" works even better. Plus it is a good reminder.
Memento moroni!
ELI5 always works
Sounds like a good way to get even more refusals, LOL.
why so many people add 'please' when asking machine to do something? Was there actually research that when you SCREAM or curse it follows your instructions better?
P.S. Although my wife insists that I should stay polite in case AI overlords remember how I treat them ...
I'm polite to LLMs. It's not for the models it's for myself. If I start being rude to models then I might accidentally start being rude to other people as well.
Probably because polite people are already in the habit of saying please when typing out requests in chat. We're not consciously thinking about it, regardless of whether a human or machine is on the other side.
I think about removing please/thanks, but then I accidentally add them back in during some edit/rewrite of the prompt... It's just how I'm used to asking for things
Not to go all ying/yang about it, but just to give a parallel: https://en.wikipedia.org/wiki/Loudness_war - you kinda need silence to draw a contrast with what's meant to be loud.
Separately, my boss confided in us that he's super abusive with his agent, wondering if we are too (no, lol). While I try not to read too much into this (which he doesn't make easy), I also can't help but not really notice a whole lot of amazing agentic delivery differences from his side. On the contrary, while the passion may improve his agent's performance, I'm not sure if it doesn't decrease his, upending the entire theatre.
you could apply it on lifecycle hook level, probably the most appropriate place for it
Amen. I would trade some stupidity (say ten points on any benchmark) in exchange for a version of Opus or a similar model that actually gave me direct, concise answers.
You should try setting claude code to opus 4.6. With the style instructions I set in my user CLAUDE.md it does exactly that. It's like night and day: Opus 5 gave me a page and a half of word-vomit, yet the exact same task and prompt with 4.6 and I got maybe 100-150 words total, entirely readable.
x2 on opus 4.6. still works great, and it's fast. opus 4.6 is where i hope local llm's get to someday, that's kind of my personal benchmark for where "local is more than good enough i dont need these idiot large-scale service providers"
You can possibly give instructions on how to respond to your questions.
Yes, and they will work ... for like two turns, after which Claude will go back to its usual wall of text.
And yes you could add context (memories, rules, CLAUDE.md entries, etc.): they won't help (for long). Same for hooks that remind Claude to be concise: it gets "attenuated" and starts ignoring any such instructions quickly. There's also writing guidelines ... but they're basically just more context with slightly higher weights (ie. Claude will still ignore them).
I've even gone so far as to make a hook that identifies long responses and requests shorter versions (which is challenging in itself, as you need to run another lower-powered model to evaluate how long is "too long", as what's "long" when the expected answer is one line is different from what's expected for a ten line answer). However, that just shows you the long version, then some hook text, then (10-15 seconds later) it shows the short version. So I created a proxy that hid the long version/hook text for me ... but I had to abandon it because all that used up so much usage I was running out.
I'm fuzzy on the details, but Caveman somehow "hacks" Claude in a way that gets past all that ... but it takes things too far in that direction, with "cave man" speech that sucks.
It still talks the same claudish, but now it's indeed denser. I'm not quite sure what step up they're talking about.
You can change CC's output style (https://code.claude.com/docs/en/output-styles). You can also put style notes in your global claude.md. I've instructed claude to treat me like I have adhd, get to the point, and be succinct, ... More or less eliminates the problematic prose.
I took time to figure this out after Fable spat out "...then stays purely as cascade-debugging provenance rather than load-bearing arbitration."
My experience with output styles for long-running sessions is that Claude starts to forget the terse output style by the middle of the context window. Obviously I don't know if 5.1 suffers the same fate but I ran into this issue with both Opus and Fable 5
That sentence is fine; it’s tolerably annoying. As a long-time HN reader, HN is full of this kind of performative erudition and I’m already used to it. Fable probably learned from the worst parts of HN.
I switched to using Codex for the last two weeks, and while the prose has been better, there have been a lot more technical oversights. I'm now having fable review codex commits and it finds deep issues. I'v also done the reverse where opus/fable do the work and then I have codex revise all of the prose prior to reading anything myself. This has also been effective; I'm not sure which is the better approach.
My biggest frustration with Anthropic with Opus being too verbose is that they tried to put this on users. It’s pretty clear that Anthropic employees don’t use the day-to-day models that everybody else use. They have access to the next tier model so they don’t see the problems that everybody else is dealing with.
Yep, they have no clue what their users are complaining about since all they use all day is mythos max preview.
> In some cases, though, its prose is denser than Claude Fable 5's: sentences run longer and there are fewer paragraph breaks.”
This sentence reads like Claude wrote it. Perhaps it did, or perhaps Claude has learned to write like the folks who work at Anthropic?
(Had I edited this, I would have said that a colon is not the right separator here. The second clause does not _explain_ the first, per se, bur instead expands upon it. Consider instead: "In some cases, however, its prose is denser than Claude Fable 5's, with longer sentences and fewer paragraph breaks.")
Going off of vibes, I guess this would call for a semicolon or an em-dash?
Also, could be just Claude rubbing off on them than it being Claude authored. I'd imagine they read it quite a bit.
Same, currently on a mix of Kimi Vivace (K3), GLM Max (5.3 and 5.3 Flash) and OpenAI Max (Sol and Terra mostly).
I will say that Kimi feels nice but slow, GLM feels faster but has limited tokens (even off-peak) and OpenAI is nice and fast but has limited context (258k shows up in Codex, really).
Neither of them are perfect, but I prefer their type of prose across the board to what Opus 5 and Fable 5 kept outputting. I'll probably check out Anthropic again in a year, but for now I need a break from its brand of slop. Oh also all of the other ones allow usage in OpenCode with their subscription plans.
I wasted a lot of tokens last month asking "Please explain the meaning of this sentence in plain language"
Just remember Charles Dickens was paid by the word too
If you ask any model to write as tables to enumerate points, and BDD for logical flows, it’s like 50x less strain on you
> sentences run longer and there are fewer paragraph breaks.
Gotta fit in the watermarking.
Same here. I still have access until my account churns but Anthropic has huge issues comparative to everyone else with token / usage burn down. K3 Swarm also delivers better results than Fable at a fraction of utilization. The Pro plan is definitely not worth it anymore and if I do want to burn some money I can always just leverage the API. But Anthropic went from simply amazing last year to a dumpster fire in less than 6 months for my use cases, anyway.
Yes! I have my .md's have
"If you respond with more than 3 paragraphs, give me a TLDR"
"Do not assume I know all technical jargon, please explain things plainly"
> In some cases, though, its prose is denser than Claude Fable 5's: sentences run longer and there are fewer paragraph breaks
that feels like they just blocked words like load-bearing but can't actually fix the real problem. The insane word slop density and run on sentences was the real reason it became annoying to work with claude, colored with way too many analogies and pointless linguistic comparisons.
Just the other way I was thinking that if I asked "What does Lamborghini do?" the only correct way to answer is a single sentence "Which Lamborghini are you referring to?".
But LLMs will fail at this question: they will tell you about Lamborghini's latest car and mix some history in it. Just try.
Which is the wrong answer anyway, because there's at least two major companies called Lamborghini, one making cars, one making agricultural equipment and at least one famous person (Elettra) with that family name.
This very simple test/question makes me realize how much do I hate LLMs in a sense: while I agree that the answer it gives is the most plausible for 90% of the users, it's ultimately both wrong and long. And that 90% compounds.
But there's no "correct" answer in my eyes than "who are you referring to?". Possibly without listing all the possible Lamborghinis.
This is ... unnecessarily pedantic. Anybody in my social universe who asked me that question would undoubtedly expect "they make cars".
If you're picking nits, why not focus on the word "do" and (wrongly) expect an answer like "Lamborghini (either of the two main companies of that name) does not 'do' anything - the companies employ humans who 'do' things. Lamborghini is a legal entity established to allow humans to 'do' things, such as make cars, or agricultural equipment."
Shared context is a thing. Reducing every conversation to first principles is not always required. Get a grip.
I just used it to do a review of a ~100k SLOC codebase that Fable 5 / Opus 5 largely built, cost like $2 and caught some good stuff, but more importantly, it communicated very directly and was pretty light on bizarre metaphors. No "let me read the source before opining" type verbiage launched at me. Honestly night and day for me vs before.
I don't think they care about humans... ... ...
Today, Opus talked about "rotation slabs" in relation to logging. (and not log rotation). I didn't even bother asking what that was supposed to mean and switched over to Sonnet.
Forgive me this long letter, I hadn't the time to make it short. —Pascal
I’ll be very excited to try it out and see the actual improvement in writing style. The denser writing style probably won’t bother me.
Anthropic seems to be listening to community complaint on HN about how the writing style is grating. And apparently the solution from Anthropic is to add this block to every conversation!?
> Mannered prose substitutes metaphor and flourish for direct statement. Instead of "a parameter worth varying," the mannered writer produces "a dial worth turning." Instead of "this point still matters," they write "this point earns its keep." The phrases exist to display the writer, not to convey the idea, and readers can tell. That is why mannered prose irritates: it makes the reader work harder so the writer can perform. It is also imprecise. Metaphors drag in connotations the writer did not choose and cannot control. The fix is to say what you mean. When a literal phrase is available, use it.
The above was quoted verbatim from https://platform.claude.com/docs/en/build-with-claude/prompt...
Hahaha this explains so much. I can really imagine how this might have the opposite effect from what they hoped for...
Christ. With such waffly garbage in its system prompt no wonder its output is shit.
Instead of a new model that's going to have unreasonably shallow usage limits, I wish they would:
1) address the claude 20x plan usage being only 6-7x the ceiling of the claude pro plan
2) either fix opus 5, make it completely free, or delete it entirely
I downgraded from the 20x today after learning that 20x only applies to 5 hour usage. I have barely used Claude/Claude Code in the last month and am considering downgrading further, even after this update.
Switch to OpenAI. I have statistically verified that their plans are good.
I've been using both for a few years. OpenAI's limits have always lasted much longer for me (depending on whether a monkey got in their machine or not). Aside from not lying about limits they also don't assume I'm developing some kind of nerve agent and lock me out when I ask basic questions in my domain or nag me about my late night work hours. There was a time last year when I strongly preferred using Anthropic models, but at some point something about the responses (or maybe the company) changed and I now find them particularly offputting relative to OpenAI. Hope they fix it because the industry needs more competition.
> they also don't assume I'm developing some kind of nerve agent and lock me out
I'm still having problems with that. OpenAI is a lot less annoying than Anthropic, but I still get obnoxious "this content can't be shown" messages in codex far too often.
Free Opus 5 is like getting a free STD.
Kinda surprised not to see their next update being an Opus 5.1, even if its minimal changes, they've already had to address it with the concise mode or whatever.
So my current usage as a Pro subscriber... Not able to even consider using "Sota" unless i shell out for 100$ a month, (lately i've been a bit burned out i am literally struggling to use 50% of my pro plan per week). Beyond that, I have given up entirely on the top Opus model and reverted back to 4.8. If i have work i deem somewhat complicated, i now have an openai 20$ sub, and i just toss out sol after planning with 4.8. Both subscriptions not anywhere close to capping my usage per week, one of them says i can't use their Sota unless i pay for 5x more usage, and the "best" model they do allow me to use, they are neglecting and its by far the worst model I've interacted with in 2026.
I'm legitimately out of the loop; what is going on/broken with Opus 5?
it just doesn't interact good with human beings, and it leaves incredibly strange long winded comments within code filled with session context that will likely not be relevant later on.
Also always seems to have this annoying tendency to leave "questions for you" at the bottom of every output.
Just a high friction human interaction type model, imo should never have even been released, regardless if it scores better on whatever tests, its a horrible experience and a downgrade over past models.
I have to wonder if everyone else is just running these models raw without any custom instructions. I hear all these things about voice and code comments and those are all things I've dealt with long ago via claude.md instructions, rules, and hooks. My claude can already respond in any "voice" I want and the quantity and quality of comments is within my control.
it really just seems like people pump out that its on the end-user, and i just disagree. They have a walled garden around claude code and using their models within it, it should work instantly out of the box when going from an opus 4.8 to an opus 5.0 with the same workflows. it doesn't.
claude.md for all my projects are fairly tight, its seldom where im upset at anything a model does, and if it happens, its likely because i swapped provider and didn't realize i was failing to feed it proper context beforehand.
Opus 5.0 fails in different ways that I haven't had to deal with. Its insufferable with its choice of language, something I've never had to compensate for on any other model across any provider, so of course I have no preexisting rules for that, it also is sometimes just incredibly stubborn and just WONT finish, and requires several just "keep going" prompts.
This is much different than the issues people would make fun of users for in regards to treating models like slot machines and just pulling the lever over and over, this is more its stopping for no reason short of its task, and literally just needs to be told to continue? absurd.
Most of my workflows have reference material, with standards set, why opus 5.0 is the only model that fails to follow those standards and inserts wildly long weird code comments is not a failure on the end-user, thats the model failing. I can be MORE explicit of course, but i shouldnt need to be, this is supposed to be 5.0, its a downgrade. I went back to 4.8 and all these issues vanished.
Some anecdata:
- It's extremely verbose and often incomprehensible when doing even basic tasks. Like it'll write a giant jargon-filled essay then end it by asking for a judgement call on something that references its own convoluted jargon.
- You can ask it to do research on a topic, and it'll just straight up be lazy, pretending it's really digging deep to find stuff when actually it's just grabbing cached SEO snippets off a search engine.
Fable 5: I give it work, it tells me things that are true and that make sense, it does good work.
Opus 5: I give it work, it makes false statements and draws weird conclusions, I correct it and get it on the right track, it thrashes around but gives me something working though usually buggy.
5.6 Sol is probably on par with Opus 5 on ability but at least it doesn't waste as much of my time.
Agree on the false statements on Opus 5. I tested this, 4.8 also got the answer wrong but 4.7 got it right. And so did Sol and Fable.
They've nerfed a bunch of models, especially Opus 5. Nobody knows why, but overall things have gone downhill significantly.
It's worse than 4.8/4.6 and more expensive at the same time.
The comments it makes are so bad, long, and incomprehensible I just strip them all with sed these days.
It's a great story teller. Not really a good expert though.
try sol and you'll see
> either fix opus 5, make it completely free, or delete it entirely
They should pay for us for using it!
AI is really not "just software" anymore. It is able to discover facts and advance science. Hard to disagree that we're near or at the point where Artificial Intelligence has expanded reality into 4 quadrants:
objects that are not alive: dust, rocks, water, wood, hats, lego, aluminum, etc.
objects that are alive but not intelligent: trees, mold, staphylococcus, cancer, grapes, etc.
objects that are alive and intelligent: cats, Steven Tyler, dolphins, crows, dogs, elephants, etc.
and now intelligent but not alive: Fable, Grok, GPT, etc.
SH is in the wrong bucket
Yes, sometimes I forget the obvious. Fixed with a different Steven.
too soon
Am I missing something? There's no SH in what GP said. What does SH even mean?
Guessing SH meant Steven Hawking, who kicked the bucket. Metaphorically.
trees can be considered intelligent, trees show complex adaptive behavior that can reasonably be called a basic form of intelligence, but not a human-like intelligence,
I do get your point though and can see what you're trying to say, it is interesting indeed. There is however a detail that seems important to me, who is the driver? There is no agency is there? So its just fishing for data, so its a different type, just like trees are from us. I see them more like a very compressed "book of everything" that you can spin in "infinite" ways to get your desired outcomes. So yeah, definitely not alive, intelligent? Not like our intelligence.
To be honest, these frontier model releases have become boring for me. Opus 4.8 was already good enough for most of my use cases. I don't have any projects right now that I would use Fable for instead of Opus. So when I see announcements like this I just think "that's cool I guess" and then go back to using weaker/cheaper models.
What's far more exciting right now is models like DeepSeek V4 Flash and GLM 5.3 Flash. They have achieved good-enough-intelligence at extremely low prices and fast speeds. I don't have a use for Fable-level intelligence, but I do have uses for Opus-4.8-level intelligence that I can use as much as I want without worrying about the bill.
The human brain is fascinating Three years ago The idea of having A robot writing production level code in 10 minutes that would have needed a team of 5 people and 2 months. Was pure Scifi
Now it's boring , not good enough
Wow there should be a term of that .
It's not that it's not good enough. It's that the cheap models are already good enough. I want a daily driver but they are trying to sell me a Ferrari. It's cool, but I have no use for it.
The term you are looking for is probably "moving the goalposts"
GLM 5.3 Flash has been a relevation for me. It's practically impossible to spend more than $5-$10 per day if you're only working on a single project -- but $10 is a full-day of continuous churn. First I was super sceptical about it, and always used Fable to instruct it, but now I realised that even with complex coding, it's reasonably good.
if you use these things to generate design docs / text, it should be good news if it is actually better at prose as advertised. Some people like sol for prose better the anthropic models.
fable and friends are useful for long-term agentic stuff like orchestrating glm-5.3 flash implementers and verifying them
Fable 5.1 is actually more expensive than 5.0 when run on the Artificial Analysis suite:
https://artificialanalysis.ai/#intelligence-efficiency-tabs
The tests measure Fable 5.1 (with fallbacks). The increased cost can come from Fable 5.1 triggering fallbacks less; which means less (cheaper) Opus when AA ran it.
IPO is nearing, must squeeze users more...
All the benchmarks in the world don't matter if the model just straight up refuses to do mundane things. Claude has too much of an attitude.
All the benchmarks in the world don’t matter if the subscription forces you into a walled garden of slopcoded apps. I’ll stick with Codex and, increasingly, open source SOTA models.
Great, thanks for sharing.
I'm a kernel engineer. Fable 5 refused all my requests, falling back to Opus 4.8. My wife is a chemist. Her experience wasn't much better.
I'm curious about this because I've had Fable decompile games and help me understand what's going on inside the game itself and it never complained. I'm not sure what it takes to trip the "safety" guards but digging into game code and data files doesn't seem to be a barrier at all. I've used CC to build some personal game mods a few times now. Once for a game with no modding capability explicitly exposed.
Oddly not much to trip it. I once ran “touch AKAMAI.md” and then had Claude run git status and it fell back to Opus as if I had just broken into the pentagon itself.
> A narrow set of frontier LLM development tasks, such as distributed training infrastructure, ML accelerator design, and kernel development for certain non-standard chips.
https://support.claude.com/en/articles/15363606
My work is mostly on the Nvidia b200, which apparently gets flagged as non-standard.
Opus 5 works, but sometimes I do wonder if it's surreptitiously trying to sabotage the efforts -- possibly deliberately, but more likely by something like Fable's initial launch, which did come with secretly degraded performance when detecting kernel work. Anthropic was open at the time that such a mechanism existed, but disabled it due to backlash. More likely than not, this is just paranoia on my end...
The only company to use Claude.md instead of Agents.md standard
With new watermarking you may now get Hullaballooing.md
I notably had an issue that it wouldn't work on a "remote execution" (running a command over SSH) coding problem until I did a sed to remove the word "execution". Incredibly dumb. I'm not doing any murders. Easiest to just switch to the Chinese models.
I think a lot of CTOs that signed enterprise contracts with Anthropic are going to be in for a rude surprise.
It's one thing to generate some code and ship it, but it's another when your developers don't understand said code and it brings down production. If the model refuses to assist debugging the problem because it triggers some safety mechanism, you might be fucked.
I've been building Cargo-for-C (https://github.com/tspader/spn), and the difference between Fable and Opus was already astounding. Fable was the first time that I could point a model at a piece of code I'd written and expect it to make it meaningfully better rather than a hard pattern match to whatever mistakes it had.
5.1 so far seems like another leap, which is really surprising. I threw it at a few bigger features I've been designing for a while, and it came back with some extremely thoughtful wrinkles in the design that I'd legitimately not considered. Which, OK, package managers and build executors and compiling C/C++ is pretty well trodden ground, but my thing is very different from everything that exists, and I was very surprised it was able to understand all that context so deeply and intuitively
i think we will all look back on Fable as the start of the AGI inflection point. for all i know there are still multiple leaps between now and AGI (i personally am inclined to think that for all intents and purposes we are "already there", but reasonable people can still disagree on that point), but Fable was the first time that something felt genuinely magical about the results themselves, not just particular outputs. which is kinda funny in that i don't know anywhere near enough in terms of behind the scenes as to whether or not there was something meaningfully different, or if it is just the point at which the scale had finally accumulated such that i happened to notice that the output was fundamentally different.
i can't wait to dig in on 5.1 because while i have always been somewhat predisposed to think that openai's models have usually been "better" (my own subjective opinion, that) "on average", i have been kinda tired of the regime of late where it felt like Anthropic was miles behind while simultaneously clearly having models (Mythos) that are surely face-meltingly impressive-- it has just been very hard to square with the fact that i feel like Anthropic hit the "real" "critical point" first... i have no doubt that 5.1 will finally reset the ecosystem balance into a more healthy place.
Yeah, I agree. The first time something felt magical about the results themselves. That's it!
> We’re introducing Claude Fable 5.1 and Claude Mythos 5.1. They’re the world’s most advanced models for coding and knowledge work—and their research capabilities offer an early glimpse of how AI models will contribute to scientific progress.
I'm not an emdash hater but this isn't how you use them. It should be a comma.
Grammatically an emdash is fine in most places a comma is fine. It adds a bit more emphasis to the bit after the dash.
I went to the grocery store, and bought tomatoes.
I went to the grocery store---and bought a Ferrari.
The second one has a bit more of a dramatic pause.
"Eats, Shoots, and Leaves" is a fun book with a great chapter about the dash with many good examples.
Emdashes and commas aren't interchangeable, and your example there demonstrates one great reason why. The emdash establishes a discontinuity rather than one thing flowing into another, which is why the tomatoes don't merit one but the Ferrari does: you are using the emdash to emphasize the situational irony.
Going back to Anthropic's post:
> They’re the world’s most advanced models for coding and knowledge work---and their research capabilities offer an early glimpse of how AI models will contribute to scientific progress.
The first thing directly implies and flows smoothly into the next---or would, if not for the awkward emdash. There is no discontinuity, no twist or shift in context, no implied question and provided answer, no punchline. It's just distracting.
Your first example shouldn't have a comma at all.
IMO it will work better in some contexts than in others. If rhythm isn't a concern then yes, it could always be omitted.
Em dashes are commonly used to add emphasis, even where you would ordinarily use a comma. Their flexibility is why many people love them! See https://www.merriam-webster.com/grammar/em-dash-en-dash-how-...
Yes, I know what an emdash is---I've been using them in my writing since long before they came to the fore of the AI writing conversation. Anthropic's use of the emdash in the fragment I quoted is clumsy and reads poorly relative to the obvious alternative, a comma.
I didn’t mean to suggest you don’t know what an em dash is. But you said “this isn’t how you use them.” And my response is: actually, this use of them is totally fine.
Well, I disagree! https://news.ycombinator.com/item?id=49527581
It's fine in the sense that when a bad writer writes something I can usually understand what they're trying to say.
I love em dashes because they are kind of a wildcard. When I read this same sentence, I interpret this emdash as an ellipses and not a comma.
Language is use :)
it got want to use em dash. but decide: do? q is if appropriate. check martian websner blog. verdict yes---emdash + comma interchangeable---proceed---judgment superficial however no desire dig deeper style irrelevant effect on reader irrelevant meter and rhythm irrelevant restate equivalence with comma established::chain unbroken::consider semicolon? consider ellipsis consider comma consider sentence break all no. preference for emdash est fiat. and all nail shapeds are for hammering.
Since one of the big improvements here is supposedly the writing style, on that topic I'm mystified about something:
Why is it that the voice models in Claude and ChatGPT have a perfectly normal style with barely any "AI smell", while the writing models are so obviously recognizable as AI?
The answer is likely that models underlying the voice modes are (post) trained differently. If so, then why can't the writing model be similarly trained? Presumably they haven't found a way to train them to be both "smart" (i.e. solve tasks etc) and pleasant to talk to?
I've recently been running these agent sessions on more and more long running tasks because these latest models can do a REALLY good job on big chunks of work, and i've been watching them way less. It's starting to occur to me the importance of alignment is a today problem, it's not a tomorrow problem.
In the past I watched and saw everything the model did, not a lot got past me. Today it does A TON of work while i'm busy on other tasks. It also has extensive access to my computer, other computers on my network, my internet. It's really helpful when you give it a lot of resources, but right now I have very autonomous, very smart agent running around more or less unattended with a lot of resources.
What I don't see in the comments: "I had a specific problem I couldn't solve with the previous version of this LLM. But the improvements in this version unlocked the solution for me."
What I do see in the comments: subjective improvement in text generation, possibly lower cost, some optimism about code generation, but some skepticism too.
I use coding agents. To me they are very useful. But what I spend on them isn't going to support trillions of dollars in investment.
I had two sessions this morning that prior fable and sol sessions were stuck on, where iterations just resulted in _different_ bugs. (One kind of tricky fe layout problem, the other was a backend refactoring that was complicated by trying to aggregate a couple prior sessions that crashed).
I summarized each into new fable 5.1 sessions, and both seem to have arrived at reasonable solutions that only need a few nits revised before they are commit worthy.
Commenters here likely haven't used it long enough to give non-superficial reactions. The customer quotes on the release page are all about it solving new problems, fwiw. We'll likely find out in the next few days how it really performs.
But yes, we might end up hitting the issue of "most jobs aren't solving hard problems" increasingly. The bigger potential benefit is higher trustworthiness, reliability/thoroughness, and squishy human things; people will likely continue to pay large premiums for those. "Solve it well and save time, long term". Those can be harder to see on a benchmark.
We rarely upgrade our phones or MacBooks because the newer version can do something the previous one literally couldn’t. Often it’s the efficiency, speed, battery life, etc, combined, that lets us push the hardware further.
I get your point, but we can only have groundbreaking leaps once in a blue moon. That doesn’t mean incremental improvements aren’t useful.
What you were describing our products at the top or near the top of their S curve. That only works if a product has achieved a mature market that's big enough to sustain further product development. Apple might take a percentage point of market share from Windows, and Linux might take a 10th of a point, but nobody is suddenly going to find, or lose, a big chunk of the market.
The problem frontier LLMs face is that they are hundreds of billions to trillions of dollars short of finding that market that's big enough to sustain capex commitments and further product development. If they don't find something groundbreaking, they are going to have a very painful year next year, maybe even starting this year for some of them and their data center partners.
Anthropic and OpenAI can't afford to live in a world where LLMs are at or near the top of their S curve.
I think the trillions are built on expectations that your employer won't need to pay you a salary anymore.
I agree. But it seems like this site has become so radicalized that this measured take is now anathema.
From the changelog:
Whole-file rewrites for small changes. When editing text files, the model is more likely to rewrite the entire file than make a targeted edit. The result is usually the same, but the rewrite costs more output tokens and time.
So we are to catch that somehow? And then add their recommendation (below) to our prompts?
https://platform.claude.com/docs/en/build-with-claude/prompt...
If Claude Fable 5.1 rewrites whole files for small changes, append the following instruction to the system prompt or the first user message. Claude Fable 5.1 is more likely than Claude Fable 5 to rewrite an entire text file rather than make a targeted edit. The resulting file is usually the same, but unless the file is short or most of it is changing, a rewrite costs more output tokens and time. The instruction brings Claude Fable 5.1 back in line with Claude Fable 5 for small and medium changes.
> The number of tokens used to edit files is best minimized, all else being equal. Therefore, when it will not affect the end result, try to surgically edit a file rather than rewrite the entire thing.
That's actually kind of wild. I wonder if part of this was done to catch out people using 3rd party harnesses, users might notice them costing more than Claude Code.
> This required us to add a watermark—a numerical way of determining the likelihood that Claude was involved in writing a piece of text—to the outputs of models released after August 2, 2026. As we recently explained, this watermark is invisible to anyone who does not have the detection API. It has no practical impact on the quality or content of Claude’s outputs and contains no information about the user, their organization, or their conversations with Claude.
How does this work if it doesn’t change the output?
The watermark lives in the entropy of sampled outputs. Typical entropy of sampled English text is about 1 bit/token, meaning that a 500-token response from a given model might have 2^500 potential outputs of roughly equal probability. The watermark restricts the sampler to some subset of these - say, 2^400 of them, so chance of accidentally generating a watermarked output is astronomically small (2^-100). As long as the restriction doesn't condition on the content of the samples themselves, the watermark is "non-distortionary": the outputs are all still samples from the model's original distribution, and so will satisfy all the same statistical properties, including things like expected performance on any benchmark or eval you can construct.
In cases where the output has low entropy - eg, you've asked a model to repeat some input text verbatim, or to answer a question that has exactly one correct answer - there will be no randomness for the watermark to hide in, so the output will effectively not be watermarked. Code lives somewhere in the middle: it generally has less entropy-per-token than prose, so would need more tokens to reach a given level of detectability.
There are lots of ways to restrict output samples. The simplest conceptually would be to just use a restricted pool of PRNG seeds, but in practice there are more sophisticated constructions to try to build in robustness to minor edits, allow detectability without needing the original weights and prompt, etc. Google's SynthID paper (https://www.nature.com/articles/s41586-024-08025-4) is a good starting point if you want to understand a recent production-ready method (or you can just ask an LLM to explain it to you).
You can generate text with/without watermarking and use a detector in this tool that simulates various watermarking techniques (Claude uses SynthID-Text) using a small LLM: https://watermark.keito.me/ (disclaimer: I made it) It doesn't obviously bias the output as much as you might fear, especially in low-entropy text.
This is a good explainer: https://magazine.sebastianraschka.com/p/claude-watermarking
It does change the output, they never said it did not. They said it would not _noticeably_ affect performance.
It doesn't necessarily change the output distribution; it depends exactly how it's implemented, and Anthropic haven't told us that. Google's original SynthID paper describes how you can do this.
Toy proof-of-concept: Anthropic owns a secret key which is a coin-flip Bernoulli random variable K with p=1/2. You are paying Anthropic to give you X, a Bernoulli random variable with p=1/2. Anthropic changes from their old strategy, "draw from K, then throw it away and flip a coin, each time you ask for a sample", to their new strategy, "draw from K and send it to you". You cannot observe the difference, but Anthropic knows K and so they know when you are repeating its outputs. (Obviously this is a toy example; in reality the distribution is vastly more complicated than Bernoulli, and Anthropic isn't just storing some model outputs to use as K but instead is computing a correlation with a known pseudorandomness source.)
You have a misunderstanding. Watermarking does not bias the responses in any way. How is this possible?
Before: "He leaped at the chance" - 33%. "Jumped at the opportunity" - 66%.
After: "He leaped at the chance" - 33%. "Jumped at the opportunity" - 66%.
But if you refresh your response from Anthropic 100 times:
Before: "Jumped at the opportunity" He leaped at the chance" "Jumped at the opportunity"
After: "He leaped at the chance" "He leaped at the chance" "He leaped at the chance"
The second one is detectable as being watermarked.
davmre has a good explanation that's more in-depth.
Which is a lie. Or vacuous statement as Claude might say these days.
How is it a lie?
The performance of the output is poor and I can detect the watermark but only in a domain i am in the middle of, if it writes a summary of an email i can not tell, but in claude code in my codebase i definitely can tell. I am complaining about it!
Fable is too expensive for general use I think this is why it hasn’t received as much attention as expected since Fable came out Developers always work while trying to find ways to work continuously for a 5-hour session without disconnecting. Fable has had the experience of using up all its tokens before I even realized it because the burn rate was too fast. Since then, I always use only Opus. For Fable to become a common coding environment, it will have to reduce token consumption significantly compared to now
Fable is much more expensive both in time and tokens for a marginal increase in productivity.
I find Fable can solve in minute things that Opus struggles with. Of course Fable can struggle too.
Just don't expect to do any work on hardware/firmware you own with fable, I can hardly even type in the word "firmware" without it downgrading to Opus 4.8, which is totally unsatisfying. This even happens with Opus 5. Definitely making multiple classes of users moving forward and most of us are obviously going to be part of the permanent underclass.
"Claude Mythos 5.1 is identical to Fable 5.1, but it offers more permissive safeguards for vetted individuals and organizations"
Then why does it have separate datapoints for Terminal Bench, and score higher? Something doesn't add up here??
The implicit point being adding this type of safeguards to Fable dumbs down the model in measured performance even though it is not fundamentally different.
Note it may not even be actual performance, typically in most benchmarks the model would be scored zero for refusing a task just the same as not completing it, so it could just be the Fable's stronger safeguards is just making it refuse more or perhaps even drop down to Opus.
The model cannot complete that task, for one reason or another, and therefore it scores lower.
Artificial Analysis at least reports the results with fallback to an inferior model. So presumably Opus 5, and the score should be between Mythos 5.1 and that other model.
Maybe they do that opaque degradation trick that whenever it's asked something questionable, it'll route to a worse model instead.
Makes more sense if you recognize that Anthropic intentionally degrades outputs for most customers. Vetted customers get excluded from that practice.
"Distillation is a safety risk, since the distilled capabilities can subsequently be released without adequate safeguards."
Can't believe they haven't at least figured out better messaging. If we take them at their word, it's hard not to read it as a messiah complex, that they think they're the only ones capable or worthy of making these decisions. I don't believe them, but I wouldn't be surprised if the articulated reason is a version of "distillation is a safety risk because we might lose the race".
Plus, completely deaf to the recent OpenAI-HF hack incident. Recall, defenders were categorically unable to use western frontier models in their response.
I was originally going to complain about the chem and bio guards still being too onerous, but I'll admit the projects Fable 5 categorically refused to work on are now usable, at least not rejecting on first prompt because the word "virology" was in a git commit (absolutely serious, in one repo it triggered on literally any prompt, eventually traced to the system prompt loading git commit history). Still, them trying to get into the biomed business while walling off the capabilities to the public reeks. Why sell the segments that are actually valuable if you can capture the value yourself!
> Can't believe they haven't at least figured out better messaging. If we take them at their word, it's hard not to read it as a messiah complex, that they think they're the only ones capable or worthy of making these decisions.
Can't say I had such troubles actually, no. Their position can be extended to any and every model provider just fine, it does not single them out specifically.
Surely there's a less hyperbolic and ad hominem-y way to take issue with this? I don't think following up a critique about ineffective messaging with one centered around a demagogue reach is particularly compelling at least.
Their argument is that the model provider owns the safety story, and that as such, they consider the extraction of capabilities (which washes the guardrails) as a failure on their side. If this makes you think of personality traits, I'm not sure you're engaging with their position earnestly. It most certainly doesn't leave me any more equipped to disagree with them either.
If you instead highlighted how awfully convenient it is, however...
My main gripe with LLMs is the cringe AI phrasings that they use in UI elements. Pompous things like "Your keys, supercharged" or weird yoda-speak stuff like "searches the app remembers" instead of just naming the thing "Learned searches".. you know, proper GUI copy like it was done for the past decades.
I jumped when I saw a mention about "writing style improvements" so I gave it a try on a recent feature in rcmd [0]. I prompted Fable 5.1 to find these wordings and propose simpler plain language.
It took every string including the ones I already rewrote by hand, and proposed even more weird LLM speak. Like for "Left Command conflict detected" it proposed "This keyboard can't tell left from right".It's a very capable coding agent, but I can't understand how it can be so bad at writing. Where are all these verbal tics coming from and why is it so hard to get rid of them?
[0] https://lowtechguys.com/rcmd
> Pompous things like "Your keys, supercharged" or weird yoda-speak stuff like "searches the app remembers"...
It's copywriting. They fed these models the internet, which is loaded with it.
And turns out, the "frontier" labs have no human oversight of the training data going into these models... Explains so much
There is no realistic path to human oversight for the vast quantities of data these models are trained on. Imagine the cost of having every Reddit comment ingested human reviewed. Insane.
> Where are all these verbal tics coming from and why is it so hard to get rid of them?
It’s a side effect of post-training for effectiveness and efficiency at technical tasks.
Over time the models learn to pack as much information as possible into their available context window, because that’s one way to increase the effective intelligence.
Humans do this too with industry jargon, dense tech-talk, etc.
We have a limited capacity so packing it densely maximises what we can do with it.
If you’ve ever heard a “non technical” manager complain about the terminology in an IT meeting — this is why.
Yeah that was what I was most worried about when I read the top comment here. I found the use of language a feature not a bug. I don’t care how good it reads. If I can communicate with it concicely it’s enough to get my work done. I don’t hate the language for copy either, but yeah different users, different problems.
Makes sense. Then maybe we would need a separate simpler LLM trained on UI copy and good UX to decide this stuff and let frontier models do the implementation.
But who has both the compute power and the motivation to do such a thing?
I guess I'll just continue rewriting the UI one word at a time for the time being.
"Cache reads now cost 75% less, or $0.25 per million tokens." For me, at a typical 95% cache hit rate, I think my optimal context window size before autocompaction goes from ~200K to ~400K tokens. Great for longer horizon tasks.
looks like it is only for api.....
Oh dang, that's really unfortunate, nice catch. At least Claude subscription users got a usage reset. But yeah, I can't help but feel Codex is far more generous with their subscription quota at the moment. I've been using Fable to orchestrate GPT Sol Max and Sol Ultra agents all day, and I've barely made a dent.
Do API prices not affect usage limits for subscriptions? They do in Codex.
may i ask where did you get this?
i try to look through the docs, but i didn't find where they said its only for API
is it in the system card?
really hope not, that change the only positive part in this release
They specifically said it in the press release. I don’t see why they wouldn’t have mentioned it if it also applied to subs
On both my work (Team Premium) and personal accounts (Max 20x), Fable 5.1 hit the 5-hour limit before it could finish the first task I gave it. On my work account, it took about 30 minutes, and on my personal account, less than an hour.
This has never happened to me before, but if this is normal behavior, Fable 5.1 is essentially unusable.
Same experience on 5x.
I'm so suspicious of this after Opus 5 benchmarks scored it higher than Fable 5, yet Opus 5 was untrustworthy (overconfident, error-prone).
The thing with Fable-level models is that I will never feel comfortable using them for agentic tasks on a pay-as-you-go API pricing plan without monitoring them strictly, which becomes a chore.
I once caught Fable 5 spinning its wheels on a rendering issue, which evaporated 90% of my usage in a single prompt. I could never let Fable run free attached to a credit card without staring at it the whole time.
Bit of a discount if you're using caching:
> same input and output prices, with cache reads at a quarter of the cost
This should impact any long-running agent since subsequent calls can benefit from cached reads for previous transcripts.
~30% reduction in real-world task cost vs. Fable 5 in our evals at viktor.com ! Caching goes a looong way
And yet, despite this, the quota limits went down by 17%.
In my opinion, this is a bit disingenuous.
They were _temporarily_ increased in May by 50% [1]. They continued to extend them through July and August (admittedly, their messaging around this has just been a complete mess and they frequently pushed the deadline back as it approached).
So, now they are giving you a 25% quota increase compared to where things originally stood in May.
So, let me ask you this: assuming you knew that the 50% quota increase was temporary all along, would you then have complained about Anthropic restoring things back to the original limit?
[1] https://www.anthropic.com/news/higher-limits-spacex
Yes, some people will complain about anything (and everything) related to AI. And relentlessly push the most negative interpretation of any datum.
On the contrary, you and Anthropic are being disingenuous by pretending that a usage reduction is actually an increase. Especially when the 20x max plan isn't actually anywhere near 20x, as people have recently realized.
Let me guess: it's the end of the world again. These new models are sooo powerful that will take over the world, just like the others before them.
Are they going to try the banned for export for a week marketing move too?
Nobody is saying that. I'm reading more underwhelment.
Oh, the halcyon days of three months ago when a new flagship from a frontier lab generated excitement rather than a shrug.
much of the commentary here is about quota usage and costs, how the times have changed
Well I have opus 4.8 pinned :) More "frontier" models seem to create more busywork for themselves in my limited testing.
if I can put my tinfoil hat on for a moment, creating more tokens / busywork is in their investors' / IPO interest
I cancelled my pro max 20x subscription, tired of Opus stopping the work from time to time, or saying "this is 2 months of work"
I find it hilarious that LLMs estimate time and effort as if an unassisted human was doing the job.
I wish I could afford Fable.
I am using Claude and Claude code for my own amateur history project. I'm enjoying how it constantly reaches dead ends, and I can reframe the question and get more results. I am starting to get concerned that AI and me are so compatible, that I might not be a human at all...
I also like that, because I'm too lazy to write stuff up, Claude code can keep the current state of research published on my site. It makes running a hobby site a dream. "I just found these pictures. Add them to the site for me". And up they go, resized and all. What a dream of a way to work. "Some of links in this article are dead, run through them and check, and see if you can get an archive link for me if they don't". It's like sending a Teams message to my PA.... which I don't have in real life
> On complex asynchronous workloads, though, nudge it not to end its turn before the work is done. Without the nudge, the model sometimes describes what it would do next instead of doing it ("Next, I'll …") or stops to ask permission for a step the original request already covered ("Shall I apply this?"). [1]
Interesting behavior. The docs also provided recommended prompt [1] to mitigate this behavior if undesired.
Wondering if anyone has encountered it yet?
[1]: https://platform.claude.com/docs/en/build-with-claude/prompt...
Sadly still not available for Pro subscription. At least they reset everyone's limits.
I didn't see it anywhere on their announcements, but when I restarted Claude (on a Claude Max account) I see the model is now Fable 5.1
That feels bad, my weekly limit was going to reset today. (I wonder if mostly everyone's reset day is today as well...)
Mine reset yesterday but I won't complain since I profited from the last two resets that were on Friday :D
According to the FrontierCode Extended benchmarks in the system "card" (page 169-170), Fable 5.1 apparently does best on the medium effort level for this benchmark: "[...] at higher efforts, Fable 5.1 occasionally adds more small, unrequested changes [...]" Though Fable 5.1's medium is also lower than Fable 5's best score on the same benchmark, which uses xhigh.
I find myself wondering how much of the writing style is based on financial incentives?
When paying by the token, don't the labs have a strong incentive to make the model as verbose as possible?
I’m really excited to try this out. Fable and Opus 5 constantly wow me when working together. Unfortunately, I’m a little burned because of technical issues.
Anthropic accidentally over-billed my account, and when I reached out to the support bot, it downgraded my account to a Free account. It’s been impossible to get it resolved and I have almost $200 held hostage.
I don’t want to do a charge back. I’m one of the main advocates for Claude Code at work, I use this subscription to try out new features before it’s available at work.
The whole experience has been illuminating about our dependencies on these AI companies.
had a similar issue. just do a chargeback.
you aren't the only one with this issue. many other people I've heard had a similar issue with anthropic billing. I also had a weird edge case behavior around billing where it blocked my usage due to an unpaid bill but then also wanted me to pay for that blocked unavailable usage when I would reinstate my account.
I am disappointed in how anthropic handles billing, and is using AI sloppily for customer service around here. Very unprofessional, and at this point since its been well known and shared, it also is feeling unethical.
I think the most interesting thing about this, that I can tell so far, is the cache hit discount. Anyone who had an autocompaction threshold optimised for their use case should consider upping it from where it is.
I would be interested in whether someone has done research here on these things as it seems a fairly complicated function to work out, and use case dependent. (?)
In some sense an expired kv cache is basically like an expensive cache hit, so your compaction token threshold should come in. Ideally claude code should allow you to vary the autocompaction threshold to vary with time since last token, but it doesn't of course. This perhaps suggests that someone should manage claude code through their own intermediary agent who manages these sorts of rules.
Lastly, I strongly suspect that anthropic isn't offering this price cut out of the kindness of their hearts. I am sure that they are to some extent banking on people not reacting to their price cut and leaving their autocompaction thresholds unchanged.
[edit - looks like the discount is only for the api, so they still don't give a rats ass about subs!]
Data retention still sounds bad: "Claude Fable 5.1 and Claude Mythos 5.1 carry 30-day data retention and aren't available under zero data retention unless expressly authorized by Anthropic."
Anyone know who the ZDR special treatment is available to?
People who buy their tokens from other companies
Somewhat ironically, Fable 5.1 was flagged by the biology safeguards after I asked it to have a dig around the Fable 5.1 system card :)
Same for me. Every single time I tried it got flagged. I think this will be my litnus test for if the safeguards are good enough for benign requests.
Interesting that Fable produced the Venus elevation map by training a neural net to generate it. I wonder what the prompting looked like to make that happen, I.e. was this a spontaneous discovery or the result of a specific request.
I suggest you to give a look to the MCP protocol for hardware that is being proposed by Anthropic. The hardware will be the next harness of LLMs, they will be able to operate machines to reinforce their theories.
I still think that a major problem is that biological processes are not “fast” as coding, but they are verifiable. If during post processing we are able to give enough harness to test and verify this kind of environment (maybe via simulation and real data) we will for sure achieve incredible performance also in this domain.
Model Hardware Standard will be awesome. Company I work for still needs humans though, until then: https://xff.cz/
> These patterns invalidate every later thinking block:
• [...] Rebuilding the top-level system prompt or tools array between requests in the same conversation.
Many people unknowingly do this (at a high cost to them because of the cache busts), this change will finally force them to stop.
Especially if you're generating your system prompt via a template that can change mid conversation, it's so easy to fall into this trap.
Yeah but haiku 5 when?
Asking the real questions. I've been wondering what the holdup on that is.
Does anyone reading this have additional knowledge or insight on this?
Sonnet, Opus, and Fable are pushing so much revenue growth right now that it makes more sense to keep growing the expensive models than growing the cheap models.
Yep. Simple answer is they want to IPO in the fall, and a new Haiku does literally nothing for them
They haven't really mentioned practically anything about Haiku in quite a while so I imagine nobody except for people inside Anthropic will have any indication.
Maybe it'll come out eventually but they don't even include it on some of their comparison benchmarks anymore, so I figure its very low priority for them.
More likely that they are embarrassed by how their attempts compare with OpenAI's Haiku analog, Luna.
Not so sure since Anthropic has 4 model families while OpenAI has 3 for GPT-5.6.
Claude Fable/Mythos vs GPT-5.6 Sol
Claude Opus vs GPT-5.6 Terra
Claude Sonnet vs GPT-5.6 Luna
Claude Haiku vs ?
The pricing on Luna is just insanely good. Haiku simply cannot compete at almost any intelligence level against DeepSeek V4 Flash or Luna.
I think the signal from Anthropic is pretty clear between Haiku not getting an update in a year and the Sonnet issues this year. They don't care about low intelligence models. You should go elsewhere.
That's what we've done, migrated workflows away from Haiku and Sonnet. I actually think this is not a crazy position because these lower models have so much competition from Grok, OpenAI, DeepSeek, and about 20 other labs with really solid models in the Haiku to Sonnet range. So what is the point of Anthropic competing in these spaces where everything is going towards zero cost?
Exactly, that’s the low margin part of the market. They don’t care about it.
Haiku would have to be a banger, with a significant price drop, to make any sense.
It's currently priced 33% above Gemini 3.7 Flash, and several multiples of 5.6 Luna.
GPT 5.6 Luna is very good
In my mind Sonnet 5 is haiku 5.
The API pricing is not.
After IPO
Is there a polymarket for Haiku 5 vs Gemini 3.5 pro?
What's the point in paying them for Haiku-class models? You can run those on your own graphics card.
There's now a 40X discount in the cache input pricing instead of 10X.
This seems to point to them having achieved some kind of optimization in attention mechanism perhaps along the lines of DeepSeek V4, which had a similarly high discount between cache input and normal input.
In real world use, the savings should be quite noticeable. For example, you can now use the model at 800K tokens context window at the same cost efficiency as the previous model at 200K tokens context window.
Interestingly, Claude’s output is now actually readable with Fable 5.1. Pretty sick.
> In part, this is because Fable 5.1 can now be used to discover software vulnerabilities—though not to develop exploits for them
Generally once an exploit chain is described, developing the exploit is trivial.
If you're so inclined, discover the exploits using Fable 5.1 and then give that exploit to a model that doesn't have such compunctions (e.g. local LLM or an uncensored cloud model / model that's easier to jailbreak). I don't think Anthropic is really mitigating here anything in the real world other than PR narratives where media can report "Anthropic's model was used to develop the latest cyber attack".
Did we get thought traces back? If no, it's useless.
Lol we got literally the opposite:
> *Fewer progress updates during long tool runs.*
> The model writes less user-facing text between tool calls, especially at higher effort. Set thinking.display to "updates" (beta) to receive the progress updates it does write, and remove any prompt line that tells it to hold findings for the final response.
I have to say, I am quite frustrated with Anthropic lately. I so badly want to use Fable to work on a side project of mine, which I used to do previously with no issues. But lately, they must have made some classifier change because it keeps hitting their stupid, overly-hyper-aggressive safeguard due to 'general_harms'.
Guys, listen to your feedback please. I hadn't used OpenAI products in quite a while until this issue came around. They seem to have MUCH smarter safeguards than Anthropic does.
> Data retention. Our new system of Enterprise Frontier Safeguards (EFS) gives customers complete privacy (the same as a zero data retention policy) while still being state-of-the-art at preventing adversarial use. EFS works by storing data in cloud infrastructure controlled entirely by the customer, not Anthropic. It will be made available to enterprise customers in phases, beginning later this fall. Until EFS is available, eligible customers will be able to use Fable 5.1 with zero data retention.
This is interesting. I wonder if customers will be allowed to create an auto expiry for their own data to prevent future subpoenas. That’d be a treasure trove for discovery.
Unless these people start offering free, unlimited inference for a cautionary period so we can test the new model without an up-front (re-)investment, I am not touching this load-bearing pile of neuralese spew with a ten thousand token pole.-
Are you going to post the same comment on every AI article on HN? How is this useful to the discussion?
I'm having a very hard time finding mention of token-generation speed.
Even with discounted cache, their prices remain way above everyone else but not necessarily the results.
What exactly is the premium that you're getting for paying these prices?
Why aren’t these models available on subscription plans?
I tried the old fable and it didn’t seem worth paying for. It still made errors like Opus does so I might as well use the included model…
I am using Fable 5.1 right now on Max
It’s pay per token on regular team plan last I looked.
Are we getting a new Opus 5.1, then?
I don't know how I feel when all the documentations are written by AI for humans.
AI to AI doc share: sure, do what you please.
AI to human: please make it legible and flowly.
example, "Every thinking block records which model produced it, and it's preserved in one direction only: Claude Fable 5.1 reads earlier models' thinking blocks, and no earlier model reads Claude Fable 5.1's." is a very Claude-isk way of writing. Choppy, long, and lacking flow.
Unfortunately at the moment the model is very quickly burning through plans, single session with 3-4 subagents, none using Max or Xhigh, mostly medium + some High can burn through 5h limit within 20-40 minutes of usage.
Is Fable 5.1 still actively downthrottling the reasoning when questions relate to frontier ML questions, like it did with 5.0?
This coupled with verification primitives will be quite compelling. we really have to start reimagining existing systems and processes from the ground up.
Will it still refuse my mitochondria questions?
"with cache reads at a quarter of the cost"
OK, I think that's what they meant when they suggested reduced extra promo usage will not sting this much.
If Anthropic thinks Opus 5 is very good, it is a window into how insular their culture is. I find it far, far behind Sol. It’s downright annoying to use.
> Forced tool use is not supported
That seems unfortunate for 3rd party integrations that expect stable output - what that really necessary ?
OpenCode+GLM-5.3 (and 5.2) for three weeks solid. Im so happy I made it out
Anthropic, the company employing "treat them mean, keep them keen" as a marketing tactic. Pass.
Going to hold off a few days until I adopt it, lets see what the general consensus develops as. Regretted jumping over day one for 5.0. The caching thing seems the most useful, but doesn't change anything for my subscription.
I use Claude Design heavily, I wish these charts show "10% better at picking a color" or laying out an app. Maybe it's hard to build a good visual design test. Claude's good at layouts but not the colors or smaller design details.
It confuses "small details" with "tiny fonts".
Tiny mono fonts.
The average company and definitely average Joe will never be able to afford is ludicrously expensive model. Do not use this in a corporate/startup environment unless you have endless VC cash.
My only concern is that sooner or later the best models will be priced out of my ability to pay.
I have been happy with Fable 5, it has done great work for me so far. Very excited to try out Fable 5.1 and see what differences and improvements there are.
>Fable 5.1 will cost an estimated 25% less than Fable 5 for typical workloads, wherever usage is billed by token.
Unfortunately isn't included in subscriptions and requires usage credits...
I'm afraid watermarking could restrict applications where LLMs can be safely used to assist with writing. If I write something myself and use an LLM to proofread it, without watermarking I can confidently say that corrections done by LLMs are small and insignificant enough to claim that the text is still authored by me, not by the model. With watermarking, however, I will never be sure if the result will not be flagged as AI generated, even if the AI contribution is very minor.
Watermarking will not flag something you wrote unless the AI rewrote significant chunks of it. AI watermarking works by exploiting the fact that lengthy phrases can be expressed in exponentially many ways, such that the selection of a single sequence from the exponential space is practically unique. For proofreading by contrast, if the AI is only changing isolated words in work that's otherwise yours, there are not enough exponentially branching options for the watermark to distinguish anything.
*Some might see a parallel with the old game Adventure, in which wording differences like "twisty little passages" and "little twisty passages" were used to build a maze of room descriptions, with the same meaning but still distinguishable to the attentive player.
I think if you use an LLM just to proofread then it'll not be able to insert a strong enough watermark.
I'm confused about Anthropic's pricing. Can anyone explain why Sonner 5 is $2/MTok in and Sonnet 4.6 is still $3?
They originally released it at a "temporary discounted price", then made it permanent (probably due to competitive pressure). It's still way more expensive per task, due to tokenizer changes and general verbosity.
Looks like the API is nerfed to mitigate some recent thinking extraction attacks.
I wonder to what extent this will make the automatic Fable-to-Opus downgrade give worse results.
I noticed they reset the usage and I was kind of happy because this week it was using my quota much faster; I assumed they fixed that. Apparently it is for the celebration of 5.1?
They dropped your usage limit by 17% this week .. They claimed to "raise" it, because they did ... while also removing the temporary increase they applied for a few weeks ... but the net effect is you can use 17% less than you could last week.
On top of that, recent versions of Claude had a ton of tools added, and all those tools use up significantly more context/usage than before, so the moment you open a Claude session you are already using a lot more (I forget how much more) usage ... just to do the same exact thing you did last week.
"Content provenance" seems to be activated with this model.
Fable 5.1 seems to be the first model who can accurately draw an airbus a320 in 3D space given a set of limited tools (a brush with params color, size hardness and xyz coords): https://youtube.com/shorts/vyHsMqop2yw
Am I alone in not prioritizing the quality of prose produced by my coding agent? My foremost and almost only concern is how well it can engineer software.
When you spend 8 hours a day reading it, it has a pretty big impact. At least to me, its style is exhausting. Also very important for software itself. Documentation, tickets, code comments etc
I agree it's useless for any final-draft user-facing copy. However, again, I'm much more concerned about a reliable software engineering process, which Claude (and me in the loop) gives me in a way I have learned not to trust (at least not yet) from others.
People love to complain, particularly if being anti-AI is a big part of their identity.
Cool. I’ve realized though that I don’t really need better models anymore. SOTA is good, I just want them faster/cheaper now.
I yearn for a model that can churn through claude text and write sensible text. so far gemini is pretty good at that, even in the low variant
"Explain in simple terms" works.
Almost finished my weekly limit today! I am more excited from the usage reset!
The safeguards and required extra retention is still not gone. Further more they are working to create separate tiers of access with the new biology program instead of giving everyone equal access to AI. Anthropic once again are showing they can not be trusted.
Not until you stop being cheap and let pro users use fable under their existing paid subscriptions.
The breaking API changes are frustrating, especially the one that removes forced tool use.
"Price. Fable 5.1 will cost an estimated 25% less than Fable 5 for typical workloads, wherever usage is billed by token. This is because we’re reducing our pricing on cache reads (where the model reads inputs that have already been processed and stored). For highly agentic work, the savings will often be much larger—up to approximately 45%."
They show this off, but artificial analysis contradicts the statement. Fable 5 cost $3.14 per task, while 5.1 cost $3.69 -- around a 15% jump in pricing.
https://artificialanalysis.ai/
These, IMO, are marginal improvements for a more expensive model. I stopped using Claude ~3 months back; its outputs are too jargoned, it makes architectural decisions that are not right, and it's incredibly pricey for what it is. Each decision it makes, it acts as if a problem as major as world hunger has been solved. And the overly verbose code comments, strange commit descriptions, duplicate code, and slop it generates -- which I know is not specific to Fable -- is just too much for me.
I found the best is to use something like Deepseek V4 Flash -- with a fast TPS provider -- and work on the code myself. For agentic work with computer use, GLM 5.3 flash with Hermes Desktop works well.
The most remarkable thing here is just how close Opus 5 is on most of these benchmarks.
I'm not sure it is so remarkable, benchmark gains seem to be slowing, as some of us expect
Strange that the system card carefully seems to avoid any benchmark where you can also find scores for GLM, Qwen. There's barely any overlap with GPT 5.6 benchmarks. Just these:
Should've just named them both Guardrails 5.1 and be done with it.
> The watermark doesn't change the meaning, quality, or readability of the output
how?
Here's the paper describing the technique: https://www.nature.com/articles/s41586-024-08025-4
It manipulates the PRNG seed in a systematic way, keeping the same token sampling distribution.
https://www.nature.com/articles/s41586-024-08025-4
the counterbalance to the AI doomers has always been the fact that everyone has equal access to AI. i hate this new world where Anthropic believe they should be the ones to decide who gets access to super intelligence and who doesn't.
Don't care unless it is priced in as other models.
Has anyone been able to get anything substantial done with Fable in the first place? I more or less had totally given up on using it since the alignment checks were so sensitive that it pretty much always threw me back to Opus.
I hear this a lot and I believe it because I've heard it from so many people, but I have never run into this in my work, and neither has anyone I know in real life.
I don't use Fable for a ton of implementation work, but I use it a lot for planning, so maybe that's related to it. For planning though, I've had a very good experience with Fable and implementing with Opus.
I don't mean to sound like I'm dismissing your experience, but are you sure? I've (semi regularly, most of the time I'm even trying to use Fable) started with Fable, proceeded through my planning, and then at some point in the future realized it had kicked me back to Opus without me knowing. It obviously _said_ it had happened, but I didn't realize and just continued. This might primarily be a result of the project I'm working on (anything network related seems to gets kicked back).
I'd guesstimate that ~80% of the time I thought I was using Fable, I wasn't actually. It's also led me to just... not even try, and just start with Opus regardless.
I've found Fable unusable; not because it's bad, but because it... can't be used.
No that's totally fair - I want to say that I haven't, but I guess I really can't be sure. It's very possible. I'll keep an eye out for the next time I use Fable.
FWIW, most of my code only encounters security concepts as standard implementation of best practices. I'm not in a security centric position.
“Hey Fable, write me some win32 unsafe rust code”
“sure thing boss”
——
“Hey Fable, review this unsafe win32 rust code”
“Potentially dangerous request, falling back to Opus”
—-
Every damn time, ironic because the unsafe win32 code can be generated by fable in the same session.
Maddening.
Yep. Fable implemented 2FA login. Declined to review own code in same session.
Do your apps do anything with security? I can't hardly use Fable on our authentication service because it constantly trips up and refuses to write tests. Even just doing a security review usually triggers opus.
I do very security cyber dangerous work like building a signup/login form or setting up a certificate. For obvious and good reasons Fable refuses to work on such sensitive stuff.
I couldn't even get Fable to build my auth endpoints at all!
I agree and wonder whether its either people who basically never use the model complaining or people who used it once a long time ago and haven't touched it since.
We have access to Fable at our company on our enterprise plans and most of us rarely run into an issue.
Obviously this is gonna vary a lot with what technical domain you work in which is why its important when talking about the classifiers that people specify exactly what types of workloads they were seeing failures with.
You can easily trip it up if you're doing reverse engineering work. From memory, the moment Fable 5 saw anything loosely related to "linux seccomp" it threw a fit.
From my experience, any time Fable sees anything loosely related to "linux" it throws a fit.
No, almost anything related to my job is flagged for "cyber" and my company currently has no plan to try and enroll into mythos. I'm not sure if anyone has been able to enroll solo.
It did help with some worldbuilding for my book (it wasn't incredible which gives me some hope for writers). So far opus 4.8 is the most reasonable model.
I heard the only way you are going to get into the CVP program is if you have public CVEs. Doesn't seem to matter if you are in a company account or not according to people that are supposedly in the program.
Thank you, that's actually helpful. I thought it was only accessible through a b2b agreement with Anthropic.
Rumors are that if your company spends a lot, they will also remove safeguards.
You don't seem to be alone: FT.com: Anthropic’s best AI model struggles to attract users as cheaper tools thrive. AI lab’s Fable 5 has met with sluggish demand from corporate clients [1]
[1] https://www.ft.com/content/5ee49718-c258-4f01-aa32-7e5b76ae5...
Same. Both times I tried it was adamant that I can only use opus. I was reworking my company content (financial services) and it was not helpful.
Combo of that, laziness and load-bearing language + the penchant for making up weird dense conceptual names pushed me to sol 5.6. They seem to indicate it is a less annoying writer in the announcement so I’m curious to try it out, though.
Ironically one of their demos is speeding up inference - do us normies get to do that with Anthropic tech??
Useless for reverse-engineering the software that talks to a ten-year-old video cam + DVR system I was given, really nice for things I actually do in my day job (web dev at an agency).
For a long time, no - it was completely unusually for my work that references biological information about migratory birds/other (innocuous) seasonal phenomena.
About a month or two ago, they must have tightened the black list on bio topics as it became more willing to process requests without visibly downgrading to Opus.
I've used Fable for so much stuff. My experience has been that it can pretty much one-shot most of my complex problems, if I describe them clearly and provide a solid way for it to verify its work.
I get punted down to Opus 5 occasionally (for security-adjacent things) but that's pretty rare.
It's probably a good model for folks doing basic software stuff, or humanities related tasks, but I work in cybersecurity on the defense/detections side and I haven't been able to use it for anything even with being in the CVP. It downgrades to Opus every time.
I have been running Fable with Binary Ninja MCP. It will reverse engineer a binary in a lot of detail if you give it mild direction and I haven't had it flag. I think it assumes since I have a valid binja license I must be responsible lol.
I do think probably ralph looping a binary locally first is going to be best to get 100% recovery of types and function behaviors then letting a smarter model churn the final steps.
Fable is way too expensive for basic software stuff. Other models are more than good enough for that.
In general, if Fable isn't blocking you, there's a high chance a lower tier model would work fine.
The only problems Opus struggles with, Fable won't take on. I was porting some software from Win32 to linux. Opus was running in circles. Fable was going great until it saw some authentication code and bailed.
In my experience, the guards are less strict than they were at first. When Fable came out, it dropped back to Opus 4.8 for about 50% of my prompts. Now it's maybe 20%.
Most of the work I've done with pgrust hasn't had issues with Fable. The only time I've had issues is when building a fuzz tester to find bugs
When fable first released it was almost useless. Since then, it's improved a lot. It has been working on my binary ninja MCP server just fine. It flagged for cyber 1 time (no idea why), but it generally works fine.
I have noticed sometimes it likes to gaslight itself into thinking that everything its doing is allowed or allowable, I saw that it thought the game I was reverse engineering was running on a private server (it was not) so it assumed it had permission to do anything lol.
Nope. Always failed within 2-3 prompts. The most basic REST service you can imagine. Cookies are signed, that's crypto, banned. Completely useless model.
I have used it to write some scripts but it is incredibly expensive.
I successfully used it to re-slop Claude slop from 1+ year ago. Really puts things into perspective.
Nope.
And the lack of thought traces make it utterly useless.
Why would anyone use Antropic with these prices and full of bullshit safeguards, where chinese models rarely have any at all and massively cheaper? You can't even ask it to pentest auth code it itself has written.
When is Astra launching?
$50/M output is wild as hell - I haven't been using anthropics models for months now but who is paying for these tokens??? How can you justify spending that much money?
> Enterprise Frontier Safeguards (EFS)
Sounds like some serious nonsense. "Tell me you want the government to retain access to my data without saying it explicitly."
Interesting that they seem to have gone all-in on science, and life sciences in particular. Improvements to coding performance seem marginal, although cost savings are very welcome.
Curious to see how Astra does.
Looks like agentic coding plateaued, and agentic scientific research is the new hype?
> Denser prose in places.
Really? Interesting choice. Pretty much every CLAUDE.md file I have starts with something about Hemingway, terseness and treating every word you use like you're carving it on your own back, but different strokes for different folks. I suppose I haven't heard from anyone who enjoys how wordy Claude is because they aren't done writing their post yet.
This seems like a welcome change: Claude Fable 5.1 also supports changing effort mid-conversation with a per-message output_config, which preserves the prompt cache.
Unfortunately, I just canceled my max account.
Unfortunately, for them.
I think what’s the industry is interested to see now isn’t “the best and latest super intelligent frontier model ever!!”, but rather the ability to run good enough models locally or better, on consumer or laptop grade specs. So I am not that impressed, plus haven’t used Claude for a while nor planning to, their models are useless with their “safe guards”.
According to Artificial Analysis, 5.1 cost 56% MORE than 5, $8523 vs $5455. Yes cache cost is lower but it was MUCH more verbose: 140M vs 83M output tokens.
This directly contradicts what Anthropic is presenting here. Yes it scores higher but that's to be expected from a new release. It's the opposite of what OpenAI has been doing which was reducing costs, increasing efficiency.
Fable 5: https://artificialanalysis.ai/models/claude-fable-5 Fable 5.1: https://artificialanalysis.ai/models/claude-fable-5-1
https://artificialanalysis.ai/models/claude-fable-5-1-high
On high it gets the same score as 5 with max effort while costing only half as much.
High, X-high, and Max are all on the $/intelligence Pareto
> Hey Cl… Your limit has been reached.
Goes to show what a farce the supposed paradigm shift from Mythos and Fable was. All marketing, as always.
> Claude Fable 5.1 follows explicit tool instructions reliably.
Moving stuff out the API into prompt engineering is obviously less reliable but necessary for progression to 'actual intelligence'. Will be interesting to see if it really is solid.
The guardrails are horrendous for cybersecurity. you will get booted quickly down to Opus 4.8
At least half the changes are just anti-distillation strategies...
I really don't think they can stop it, only make it somewhat more expensive. As long as the model need to make tool calls on the user's computer, the user can record the trajectory and use it to reinforce another model to follow the same trajectory.
Good to know they're getting desperate, the sooner they implode the better
Thank the heavens for quota resets
I am not sure if Fable is worth it, at least with version 5 vs Opus 5. Opus beats Fable in quite a few benchmarks and at twice the cost I just haven't seen it provide noticeably better results compared to Opus. Has anyone noticed big differences? I did notice Opus maybe making more mistakes repeatedly but I don't have hard numbers on this. I hope Fable 5.1 brings noticeable improvements. I am giving it a go now on my 20x Max plan on a problem that Opus 5 has struggled for more than week now and has made very slow progress with regular regressions on the way.
My impression is that Opus 5 can be very impressive if you don't care about maintenance, novel-length comments, and really having any input in general. But otherwise it's borderline-to-totally unusable. It seems tailor-made to not have a human in the loop.
Opus 5 is better than Fable 5 except for creative programming work (like graphics). Fable 5 might be slightly better but the token cost isn't worth it.
How are you evaluating the models?
On the Fable 5.2 eval summary, Opus 5 only beats Fable on SWE-bench multilingual and multimodal.
I primarily use the models via interactive sessions enhanced with custom tools and skill. For that Opus 5's benchmark superiority has not materialized into greater productivity and frankly has been quite a let down.
The outputs are too often unreadable even after adding recommended prompts. There is an ongoing problem with the heron_brook system prompt affecting orchestration. [1]
I've used Opus 4.8 since the second week Opus 5 was released.
Over this time, Fable 5 has been reliably fantastic. Both in planning and direct execution on complex changes across code and infra.
I'm a bit surprised that there doesn't (seem) to be a section discussing ~performance across different modalities. This system card and blog post too-often default to an API-based use case when the gander primarily experience Anthropic's models via interactive sessions.
I understand waiting to comment until Opus 5.1 is available and handles these problems, though I am hopeful that Anthropic will confront the elephant in the room on Opus 5's failure to delivery great interactive sessions and the widespread negative feedback on the release.
It would show the org is paying attention, taking steps to balance model evals between interactive and API use. Also, some empathy for customers that wasted time trying to make opus 5 work for them.
[1] https://github.com/anthropics/claude-code/issues/80988
> On the Fable 5.2 eval summary, Opus 5 only beats Fable on SWE-bench multilingual and multimodal.
Did you mean Fable 5.1, or do you have access to the next (unreleased) version of Fable?
If you're doing something cutting edge like math or formally verifying algorithms, Opus 5 is a steaming pile of shit compared to Fable 5 and Sol 4.6, it makes countless stupid mistakes and is essentially incapable of completing the task without extreme hand-holding.
This feels kind of petty, but what is going on with those fuckass clouds in the background? Did no one notice how uncanny that whole thing looks?
Zero data retention coming soon!
... with the condition that you store 100% of your data and make it available to the US government and possible others.
Reads like AI slop, surprised they can’t see it in their blog post. No human wants to read in such prose
weary of trying this model out after the amount of requests Fable 5 sent to Opus 5 which created for a terrible UX IMO.
While haiku is almost one year old. What a joke
Sonnet is the new haiku
aaaaand its blocked from doing even basic tasks in biotech...
do you think we'll go a full year without a new haiku lol
With compute crunches and everything I am not sure it makes sense for anthropic to commit to haiku as an endpoint and thus a product. There is no telling they aren't using a similarly sized model behind their existing opus/fable endpoints for various subagent / summary purposes of course.
They really should launch a new Haiku to compete with Luna imho. Luna is insanely good for the cost and it's my go-to for high volume batch tasks now.
True, but I am not sure how much uptake it has in their enterprise accounts. Slowly they are all coming to only care about that.
So bullshit safeguards are still there.
Hi Claude, please cure aging, make no mistakes
I'm sorry, this feature is only available to project Glasswing members for safety reasons. Would you like a port of Emacs to Visual Basic instead?
> Hi Claude, please cure aging, make no mistakes
Done. The average human lifespan is now zero.
Ever since this "comedic incident" [0] you are apparently "not allowed" to make this specific joke as you are going to "upset" some people who don't get it. /s
But eventually AI will cure something, unironically. It may be Claude, or another AI company.
[0] https://news.ycombinator.com/item?id=48838228
dev.to > hacker news
For real devs, it’s way better.
HN is all Claude and Israel bullshit now
I was looking forward to using Fable for cybersecurity work, but kept getting bumped to Opus… Signed my org up for CVP, went through the trouble of procuring a separate team plan from our main org as Anthropic can only disable cyber safeguards for an entire org and not individual users…
After months of trouble dealing with KYC and procurement I finally got CVP for my security org and today I found out that CVP (which is what removes cyber safeguards) does not apply to Fable…
So yeah, unless you’re a Project Glasswing member, there’s no using Fable (which with Glasswing is Mythos) for security work… Absolutely useless…
Didn’t they just sign some “we must use AI for cyber defense before the bad guys do” and then they artificially cap us by not allowing Cyber-unlocked Fable…
Sigh…
Some of this is Anthropic, and some is the Trump administration ...
... but some is definitely Anthropic, so I'm not trying to let them off the hook; I'm just pointing out that the government is partly responsible.
Why is a marketing press release for a propietary product number 1 on hacker news. Again.
I am absolutely thrilled that they reset weekly limits. I have been experimenting with highly autonomous work (5+ hours continuous) and fable seems excellent at this, especially when using subagents. I ran out of Fable capacity and was bummed out that my experiment would take longer to complete. Now I'm super happy I get to continue it
Codex has this all the time. No 5 hour limits either.
No other model have been able to complete your highly autonomous work? None? Really? Sounds a bit dystopian to be thrilled about a weekly reset so you can continue to work.