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.

And that’s what changes the whole game — Claude

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.

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.

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.

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

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.

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.

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.

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.

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).

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.

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.

Great. I'm looking forward to it being less obvious that my colleagues have stopped understanding their jobs.

Could you share what you use internally to make Fable not sound like a word salad generator?

(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.

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?

Nice, I'm looking forward to the improved writing on the majority of articles posted here.

> 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?

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

Can't wait for the distillations! I'd love improvement on writing on cheap models

Thank you for the trust me bro benchmark but i will be honest, fable 5.0 did even worse thsn 4.8 opus

Please much more of that. The Claudish language makes me dizzy, and it's very difficult to steer the model to not include it.

claudism really sucks, Gemini and codex output so much better, way more like a real human being.

> 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.

Felix, just poking at this, and it is MUCH more pleasant to talk to, thanks to your teammates for the work.

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.

Both a fable and mythos release? I'm glad to see you take the belt-and-suspenders approach seriously!

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.

    > Fable 5.1 more than doubled Fable 5's Terminal-Bench-Science [1] score, which I think is meaningful.

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...

    "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."

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. ;)

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?

  ⎿  You've hit your session limit · resets 2:51am (123°24′W Etc/GMT+8)
  /upgrade to increase your usage limit.

I hope not! Then my t-shirt is no longer accurate :D

Do you know if Opus 5.1 is coming and will have improvements in writing style too?

I had just assumed this model would read differently due to watermarking.

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.

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.

as an anthropic employee, do you trust the benchmarks?

Thanks for your helping destroying the world!

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?

I ain't wanna see anymore websites with "The SAAS that actually [italics]Works[\italics]"

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...

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.

Qwen is all you need.

Does the new writing style now have EU level watermarks?

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.

> 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)

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."

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!

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 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.

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.

Now that it's a solved benchmark, can we get the animated version?

Curious how similar the outputs of xhigh and max are, in particular the clouds.

What’s the token usage of xhigh?

Finally we have a fish in the basket!!

A pelican is a bird, not a person. The knees bend the other way.

Even added a little hat for the pelican!

In a way, this is the only benchmark I care about now. :)

These pelicans are awful.

Do you think model trainers are pelicanmaxxing now?

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.

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

>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).

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!)

Anthropic did not get much bite because they don’t offer zero data retention with fable

> 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

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.

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....

Cut them a break. They are trying to IPO soon.

> 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.

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.

What do you mean fable is useless?

> as many of noted

please rephrase?

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

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!

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 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.

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:)

GLM 5.3-flash fits the bill

Have you tried Grok 4.6, if you're focused on token budgets? In a league of it's own for tokens/intelligence.

Try gpt 5.6 Luna max

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.

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

"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'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.

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 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."

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.

> 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.

I wasted a lot of tokens last month asking "Please explain the meaning of this sentence in plain language"

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.

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.

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"

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.

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... ... ...

Forgive me this long letter, I hadn't the time to make it short. —Pascal

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.

Software will be buggier than ever but also way less buggy.

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.

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..

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

SH is in the wrong bucket

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.

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.

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?

> either fix opus 5, make it completely free, or delete it entirely

They should pay for us for using it!

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.

IPO is nearing, must squeeze users more...

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 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.

The only company to use Claude.md instead of Agents.md standard

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.

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.

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-...

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 :)

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 on the squishy human tasks.

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.

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.

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.

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.

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 .

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

> 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.

> 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.

looks like it is only for api.....

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.

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.

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.

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.

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.

> 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...

I find it hilarious that LLMs estimate time and effort as if an unassisted human was doing the job.

~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%.

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...)

People who buy their tokens from other companies

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.

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?

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?

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.

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.

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.

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.

Model Hardware Standard will be awesome. Company I work for still needs humans though, until then: https://xff.cz/

Are you going to post the same comment on every AI article on HN? How is this useful to the discussion?

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.

It confuses "small details" with "tiny fonts".

>Fable 5.1 will cost an estimated 25% less than Fable 5 for typical workloads, wherever usage is billed by token.

I am using Fable 5.1 right now on Max

People love to complain, particularly if being anti-AI is a big part of their identity.

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

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.

"Explain in simple terms" works.

I'm not sure it is so remarkable, benchmark gains seem to be slowing, as some of us expect

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

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.

Aren't you so clever. Go to Reddit.

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.

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.

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.

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.

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

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.

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.

Sonnet is the new haiku

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.

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

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.

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.