Claude Fable 5.2 formalizes Fermat's Last Theorem in 30 hours
Claude Fable 5.2 and Mythos 5.2
Anthropic's new Fable 5.2 and Mythos 5.2 models tackle the hardest technical work: a swarm of 1,000 agents fully formalized Fermat's Last Theorem in 30 hours with minimal human input, where an earlier research version took 11 days. They also solved two open black-hole physics problems, designed three working electronic devices from scratch, and migrated a production service from Python to Rust. Output is up to 30% faster at $8/$40 per million tokens.
A team of 1,000 Fable 5.2 agents fully formalized the theorem in just 30 hours, with minimal human intervention.
- kimseungyong
The biggest relief is that the price has dropped by 20%. It’s still expensive, but with my $100 plan, Fable’s usage would spike instantly the moment I started using it, so it was always a source of fear.
I will still use opus for general coding design, but for major designs.
- postalcoder
I’ve had a chance to use fable 5.2. Some observations:
- Anthropic is finally well balanced across models. Meaning: Opus 5.5 is so good that I do not feel Fable FOMO as I did when it was Fable 5/5.1 vs Opus 4.8/5. And Sonnet 5.5 sometimes makes me forget about Opus.
- Fable is good, but you really have to push the ambition of your prompt in order to see proper separation from Opus 5.5. I personally have a hard time telling the difference between Fable 5.2 and Opus 5.5 for ordinary coding tasks.
- It’s way faster and more reliable: one of the worst things about fable 5.1 was how slow it was an, on top of that, how frequently it would suffer from max output token overflows. I got none of these issues with 5.2.
- Fable is exceptional at drawing. It’s ability to render an image with JavaScript actually has me questioning the value of dedicated image models. I prefer the images I’ve gotten fable/opus to make for me over those from gpt-image, it’s wild to think we’re at this point.
- breakwaterlabs
- Why are they stacking Fable xHigh against Carbon Med?
- How did they produce such a bizarre effort-intel curve for Carbon that goes against every available benchmark?
- Why did they leave Carbon-- positioned primarily as a cyber model-- off of the single cyber benchmark comparison?
- Why do they switch to comparing against Argon (rather than carbon) for robodojo?
- yewenjie
> Our first formalization of Fermat’s Last Theorem, performed by an unreleased research version of Claude, took 11 days. It relied on a purpose-built harness along with guidance from a human researcher. By contrast, a team of 1,000 Fable 5.2 agents fully formalized the theorem in just 30 hours, with minimal human intervention. Fable 5.2 started from minimal prompts, built its own ways to coordinate, and used no mathematical references, only a list of intermediate theorem statements to score progress. It needed one-third of the action tokens as our first formalization and produced a proof seven times shorter. As can be seen in the figure below, Opus 5.5 (with the same 1,000-agent setup) completed only 26% of the formalization in 18 hours, and barely made any more progress after 30.
Most people don't really have intuitions on what it means to push the frontier now (because AI has surpassed everything they are good at, for example, coding). We are truly inside the singularity (using Kurzweil's definition, slightly paraphrased - the time when technology progresses so fast no one can keep track with it).
- mercnz
i've been trying to use sonnet and opus to keep my usage down on the low max plan, but i noticed today that somehow i'm 80% through my weeks usage. so i'm hesistant to even try fable 5.2 yet, but finding the right set point of usage vs model size has been a bit struggle for me, one of my biggest issues has been trying to pull back doing exhaustive testing or other such things that chew through context, and instead have programs that just measure things are working, but i continously seem to run into issues with claude wanting to repeat things for itself in an adhoc manner. i've tried fable directing opus or sonnet subagents, and the reverse. and i found that part of the issue with smaller models trying to direct subagents is that they over specified what they thought the problem was rather than the problem. like they'll have an "idea" about it which is wrong, and then try and feed that into the subagent.
- bhu8
Ethan Mollick's take and early testing with Fable 5.2: https://www.oneusefulthing.org/p/fable-52-and-jagged-agi
- advaith08
We've been early testing Fable 5.2, and have been surprised by its coding ability. It was able to work with an esoteric 600k line fortran codebase to speed up some computational material science work for us by 36 times (!). Given that this could be done in 2 days, we've decided to open-source the results https://github.com/discovered-materials/dm_qe
- pookieinc
“Testers have found that Fable 5.2 and Mythos 5.2 communicate more clearly than past Fable and Mythos models. They generate outputs up to 30% faster than Claude Fable 5.1 and Claude Mythos 5.1, and they’re available at a lower price: $8 per million input tokens and $40 per million output tokens.”
Honestly incredible that they’ve managed to beat all benchmarks, while making it cheaper. Always happy to see improvements offered at lower costs.
Will be interesting to see what OpenAI does in response
- minimaxir
There were more than a few "leaks" saying it would be called Fable 5.5, so I'm curious if a) the leaks were just engagementbait or b) Anthropic changed it, despite the fact that Fable 5.2 being better than Opus 5.5 is confusing.
Surprisingly the model is available immediately in my Claude Code: usually there's a delay, either for rollout or safety.
- lhk931122
With 5.1, there practically seemed to be no difference in ability between opus and fable, but I hope there is a difference this time. When it seems to struggle while working I end up using astra, so I hope it works well.