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Claude Fable 5

anthropic.com

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Re: Claude Fable 5

#601
I am puzzled by the frontier code graph. GPT 5.5 doesn’t show any improvement with reasoning efforts. This new benchmark by Cognition seemed to be released with Fable 5’s announcement.

I am not trying to cook a theory here but it generally shows how strong Claude Opus family is. I am not saying that Opus is not powerful but it doesn’t align with my experience of GPT 5.5 and Opus 4.7.

I understand that Fable and Mythos are frontier models that can do protein folding better than task-specialized ones. To be honest, for practical point of view, for day-to-day coding assistance, GPT family looks more reasonable.

(But then my company pays for claude max anyway for token maxxing. So who am I to complain)

Re: Claude Fable 5

#602

From today through June 22, Fable 5 is included on Pro, Max, Team, and seat-based Enterprise plans at no extra cost. On June 23, we’ll remove Fable 5 from those plans. Using it after that will require usage credits. If capacity allows, we’ll extend the included window. After this point—when sufficient capacity allows us to do so—we aim to restore Fable 5 as a standard part of subscription plans. We intend to do this…

This is the entire business model of all AI companies. It costs far more to run the datacenters and build more capacity than they could ever hope to make back at current pricing models. I'm looking forward to pricing to catch up with reality and the resulting chaos that ensues.

Re: Claude Fable 5

#603
Not impressed so far, to be honest. I'm having it try to optimize Stockfish in a loop (on xhigh mode) with a benchmarking oracle; even after giving it specific hints ("consider whether we're prefetching Y optimally, can we make function X branchless"), it's been so far unable to recover any of the recent optimizations we've implemented – let alone novel ones. Opus 4.8 felt a bit more creative to me ... but a small sample size so far. I'm next going to try it on some less open-ended problems.

Edit: It did correctly identify that transparent huge pages were off in its sandboxed environment and that enabling it was helpful, so that's nice. It also noticed that we skip THP on a certain less used path.

More importantly, I'm finding that the code that it produces for its experiments is a lot cleaner than what I'd expect out of Opus; there's fewer useless comments and it's more surgical and readable. I wonder if that explains the increased scores on benchmarks measuring mergability.

Re: Claude Fable 5

#604
I was pretty excited until I read this:

> What happens when the promotion ends After June 22, 2026, Claude Fable 5 is no longer included in your plan’s usage limits. You can keep using Claude Fable 5 through usage credits, which let you pay for usage beyond what your plan includes. Learn more about using usage credits.

Re: Claude Fable 5

#605
post #534

I've spent enough time with this now in Claude Code (and Claude.ai and Claude Code for web) to have an opinion on Fable 5: it's a beast. I'm throwing some VERY difficult problems at at - things I've been dragging my heels on for months - and it's crunching through them very happily. One that I'm willing to share (albeit from just a week ago) - I built a Python library last week that bundles MicroPython compiled to WA…

This looks like a toy project, not a “VERY difficult” problem like you stated.

Re: Claude Fable 5

#606

> In light of the ability of recent models to accelerate their own development, we’ve implemented new interventions that limit Claude’s effectiveness for requests targeting frontier LLM development (for example, on building pretraining pipelines, distributed training infrastructure, or ML accelerator design). Using Claude to develop competing models already violates our Terms of Service, but enforcing this restrictio…

These safeguards are ridiculously sensitive: a prompt as simple as “ Why is an infinitely slow process reversible?” gets flagged as a ToS violation.

Re: Claude Fable 5

#607

Claude Fable 5 beats Pokémon FireRed using only vision: https://www.youtube.com/watch?v=CIQBP1w4B1M

The video is privated now, but the timelapse is weird. Sometimes it skips only seconds before the next screenshot and sometimes it skips probably hours forward.

Re: Claude Fable 5

#608

I was pretty excited until I read this: > What happens when the promotion ends After June 22, 2026, Claude Fable 5 is no longer included in your plan’s usage limits. You can keep using Claude Fable 5 through usage credits, which let you pay for usage beyond what your plan includes. Learn more about using usage credits.

[deleted]

Re: Claude Fable 5

#609
I used it for the very advanced task of picking my brackets for my company's world cup pool. I was impressed with the analysis it came back with and now I actually want to follow the games.

Re: Claude Fable 5

#610
post #534

I've spent enough time with this now in Claude Code (and Claude.ai and Claude Code for web) to have an opinion on Fable 5: it's a beast. I'm throwing some VERY difficult problems at at - things I've been dragging my heels on for months - and it's crunching through them very happily. One that I'm willing to share (albeit from just a week ago) - I built a Python library last week that bundles MicroPython compiled to WA…

What can it do that Opus couldn’t?
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