Claude Fable 5.1 and Claude Mythos 5.1

Not until you stop being cheap and let pro users use fable under their existing paid subscriptions.

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.

This coupled with verification primitives will be quite compelling. we really have to start reimagining existing systems and processes from the ground up.

Should've just named them both Guardrails 5.1 and be done with it.

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.

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.

> Forced tool use is not supported

That seems unfortunate for 3rd party integrations that expect stable output - what that really necessary ?

"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.

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.

The most remarkable thing here is just how close Opus 5 is on most of these benchmarks.

Interestingly, Claude’s output is now actually readable with Fable 5.1. Pretty sick.

Looks like agentic coding plateaued, and agentic scientific research is the new hype?

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 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?

"Content provenance" seems to be activated with this model.

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

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.

Unfortunately isn't included in subscriptions and requires usage credits...

Why is a marketing press release for a propietary product number 1 on hacker news. Again.

> The watermark doesn't change the meaning, quality, or readability of the output

how?

Don't care unless it is priced in as other models.

$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?

> 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.

"Democratization" through AI means that everyone has to pay a monthly Anthropic tax and only a small secret guild gets access to the real model.

Jane Street is a partner? How sad indeed. Anthropic could front run them because they leak all the data.

> 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.

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.

> 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.

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…

> 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.

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?

At least half the changes are just anti-distillation strategies...

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.

The biggest change is the price cut of course.

Reads like AI slop, surprised they can’t see it in their blog post. No human wants to read in such prose

While haiku is almost one year old. What a joke

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.

do you think we'll go a full year without a new haiku lol

aaaaand its blocked from doing even basic tasks in biotech...

So bullshit safeguards are still there.

[dead]

Hi Claude, please cure aging, make no mistakes

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