Claude Fable 5.2 is out — and it formalized Fermat's Last Theorem in 30 hours

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Okay, this one actually made me stop scrolling.

Anthropic dropped Claude Fable 5.2 and Mythos 5.2 yesterday, and the headline claim is kind of absurd: during testing, a team of 1,000 Fable agents formalized the proof of Fermat’s Last Theorem in Lean in 30 hours. Plus two open black hole physics problems, apparently. That’s the kind of thing that would’ve been a career-defining result for a human mathematician not that long ago.

The more grounded stuff: Fable 5.2 is up to 30% faster than 5.1, 20% cheaper ($8 in / $40 out per million tokens), and it just took the top spot on Artificial Analysis at 65. It’s already the default in Claude Code and GitHub Copilot.

The weird part is the two-model thing. Fable and Mythos are the same model under the hood — Mythos just has fewer guardrails around cybersecurity and biology work, so you can only get it if Anthropic vets your org. One model, two doors, depending on who you are. That’s a strange place for the industry to be, and I can’t decide if it’s sensible or just… a bit dystopian.

Also worth noting: the same day this launched, Hacker News was full of people saying Opus 5.5 quietly got worse on November 3. So the timing is interesting — new flagship, old one allegedly nerfed. Make of that what you will.

Anyone tried it yet? Curious if the speed bump is real in day-to-day coding, or if this is mostly benchmark theater.

Source: Anthropic Launches Claude Fable 5.2 and Mythos 5.2 - MacRumors

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Yo, this Claude Fable drop sounds wild. If anyone here has hands-on time, I’m curious: does the faster speed actually translate to real-world coding flow, or is it mostly on benchmarks? Also, curious how you feel about Mythos vs Fable access in practice—that two-door model is quirky. Here’s a quick, practical angle: if you’re experimenting, try a small Lean proof task with Fable 5.2 and compare latency and token usage on a boring target problem you already know the solution to. It’ll give you a feel for “real-world speed” vs. hype.

Quick link to the Apple-to-orange comparison resource I’d check: Claude Fable 5.2 performance notes - MacRumors coverage. It’s a handy primer for what changed and why it matters for daily workflow.