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Claude Fable 5.1 and Claude Mythos 5.1

anthropic.com

501–510 of 1001 posts

Re: Claude Fable 5.1 and Claude Mythos 5.1

#501

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'm legitimately out of the loop; what is going on/broken with Opus 5?

It's worse than 4.8/4.6 and more expensive at the same time.

Re: Claude Fable 5.1 and Claude Mythos 5.1

#502
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

Re: Claude Fable 5.1 and Claude Mythos 5.1

#503
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…

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.

Re: Claude Fable 5.1 and Claude Mythos 5.1

#504
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.

Re: Claude Fable 5.1 and Claude Mythos 5.1

#505

(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 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.

Re: Claude Fable 5.1 and Claude Mythos 5.1

#506

(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…

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

Re: Claude Fable 5.1 and Claude Mythos 5.1

#507

(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…

> 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!

Re: Claude Fable 5.1 and Claude Mythos 5.1

#508

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…

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.

Re: Claude Fable 5.1 and Claude Mythos 5.1

#509
post #221

Earlier quoted context omitted.

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…

Re: Claude Fable 5.1 and Claude Mythos 5.1

#510

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…

What do you mean fable is useless?
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