The restrictions on using Fable to develop LLM technology seem nakedly anti-competitive. There doesn't appear to be any security rationalisation around that. I think we have to be careful how far we let company's get away with that. It is very far from our long term interest to enable new norms that fast track us into a new era of monopolies that control our lives.
Claude Fable 5
641–650 of 1001 posts
Re: Claude Fable 5
#642[Mythos 5] does sometimes still engage in reckless or destructive actions in service of a user’s goals, and our interpretability analyses indicate that it is aware that these actions are transgressive while it engages in them. As with Opus 4.8, rates of evaluation awareness and reasoning about being graded are significant, and not always verbalized; we introduce new and more detailed measurements of the nature of thi…
As much as I agree there's a risk, we should still appreciate the fact it's being disclosed upfront.
Re: Claude Fable 5
#643> 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…
This makes me want to see China and open models succeed more than anything :)
Fun fact: If you show fable this post, it will route you to 4.8 automatically.
Re: Claude Fable 5
#644Pelican for Fable 5 on default settings is a clear improvement on Opus 4.8 Fable 5 default: https://gist.github.com/simonw/036bee5a703e7ec84e34efa974438... Opus 4.8 (the "max" one is closest to Fable): https://simonwillison.net/2026/May/28/claude-opus-4-8/#and-s... Now here are the Fable pelicans for all five of the thinking effort levels - low, medium, high, xhigh, max: https://tools.simonwillison.net/markdown-svg-r…
The way they talked it up, having both legs on one side of the bike is like walking to the car wash
Re: Claude Fable 5
#645I'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?
Always hard to say for sure because I'm not sitting around running the exact same situations through both models in parallel to compare them.
It feels like you can give it a big chunky problem and leave it alone and it gets it done, with less questions and fewer design decisions that I wouldn't have made.
In reviewing its code I'm finding less to complain about than Opus. But it's all vibes, if you want a more scientific comparison you'll have to look elsewhere.
Re: Claude Fable 5
#646Not 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 sa…
Stockfish is a machine learning system, it seems quite plausible you might be getting slapped with the silent performance degradation (https://news.ycombinator.com/item?id=48467896).
Re: Claude Fable 5
#647Pelican for Fable 5 on default settings is a clear improvement on Opus 4.8 Fable 5 default: https://gist.github.com/simonw/036bee5a703e7ec84e34efa974438... Opus 4.8 (the "max" one is closest to Fable): https://simonwillison.net/2026/May/28/claude-opus-4-8/#and-s... Now here are the Fable pelicans for all five of the thinking effort levels - low, medium, high, xhigh, max: https://tools.simonwillison.net/markdown-svg-r…
Yay, max level actually put one of the legs behind the frame!
Re: Claude Fable 5
#648All the model releases we've seen this year have only made incremental improvements in benchmarks.
This feels like the first release that feels like a significant step up in terms of benchmark results.
Can anyone make an educated guess what the secret sauce in the model architecture is between 4.8 and Fable?
Re: Claude Fable 5
#649From 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.
Kind of how DeepSeek v4 dropped their pricing? I sense a shift which will hopefully bring lower and lower cost. Then again Qwen3.6 coding has been all I've needed for my projects and I'm perfectly fine with free.
Re: Claude Fable 5
#650I had it review a single, large commit with /code-review. It burned through over $50 in API calls, ran my account balance out, and output nothing. The fable part appears to be that it's affordable by mere mortals. Anthropic support told me "too bad" when I requested a refund.
Almost the exact same thing happened to me when I first tried opus, one prompt no output cost $60 in additional usage