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Claude Fable 5.1 and Claude Mythos 5.1

anthropic.com

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Re: Claude Fable 5.1 and Claude Mythos 5.1

#431

Post by spwa4 »

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

Re: Claude Fable 5.1 and Claude Mythos 5.1

#432

Post by mywittyname »

bryanlarsen wrote: post #276
felixrieseberg wrote: post #69

(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…

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 compu…

> 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.

Re: Claude Fable 5.1 and Claude Mythos 5.1

#433

Post by 5555watch »

felixrieseberg wrote: post #69

(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…

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

Re: Claude Fable 5.1 and Claude Mythos 5.1

#434

Post by anygivnthursday »

velcrovan wrote: post #121
felixrieseberg wrote: post #69

(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…

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 lef…

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.

Re: Claude Fable 5.1 and Claude Mythos 5.1

#435

Post by jbs789 »

exabrial wrote: post #419

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…

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

Re: Claude Fable 5.1 and Claude Mythos 5.1

#436

Post by fschuett »

vunderba wrote: post #407
peab wrote: post #191

Earlier quoted context omitted.

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 a…

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.

Re: Claude Fable 5.1 and Claude Mythos 5.1

#437

Post by cheesecakegood »

adastra22 wrote: post #301
felixrieseberg wrote: post #69

(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…

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.

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.

Re: Claude Fable 5.1 and Claude Mythos 5.1

#438

Post by fock »

ademup wrote: post #325
adastra22 wrote: post #301

Earlier quoted context omitted.

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.

Great news, then! TFA: "Last week, we previewed the Model Hardware Standard, which allows Claude to directly and safely operate laboratory equipment."

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)...

Re: Claude Fable 5.1 and Claude Mythos 5.1

#439

Post by hyperpape »

verdverm wrote: post #326
giancarlostoro wrote: post #136

Earlier quoted context omitted.

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 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...

Re: Claude Fable 5.1 and Claude Mythos 5.1

#440

Post by george_max »

pookieinc wrote: post #9

"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%." Glad to see this!

This is just cache reads. In real usage it costs 15% more than Fable 5 -- all for marginal gains.

https://artificialanalysis.ai/

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