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Claude Fable 5.1 and Claude Mythos 5.1

anthropic.com

61–70 of 1001 posts

Re: Claude Fable 5.1 and Claude Mythos 5.1

#61
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

Re: Claude Fable 5.1 and Claude Mythos 5.1

#62
post #22

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…

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.

Re: Claude Fable 5.1 and Claude Mythos 5.1

#64

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.

Re: Claude Fable 5.1 and Claude Mythos 5.1

#65
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.

Re: Claude Fable 5.1 and Claude Mythos 5.1

#67
post #35

“ 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…

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.

Re: Claude Fable 5.1 and Claude Mythos 5.1

#68
post #22

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…

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.

Re: Claude Fable 5.1 and Claude Mythos 5.1

#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 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

Re: Claude Fable 5.1 and Claude Mythos 5.1

#70
> 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.

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