1,000 Claude agents formalized Fermat's Last Theorem in 30 hours: Fable 5.2 is out, faster and cheaper
Anthropic released Claude Fable 5.2 and Claude Mythos 5.2, the same underlying model with different safeguards. Fable 5.2 is open to everyone and is built for the hardest, longest technical work. Anthropic says it writes up to 30% faster than Fable 5.1 and now costs $8 per million input tokens and $40 per million output, down from $10 and $50. In pre-release tests a team of about 1,000 Fable 5.2 agents fully formalized the proof of Fermat's Last Theorem in Lean in 30 hours, and one engineer had it coordinate over 1,000 subagents for eight days to build a prototype operating system that boots on a laptop. Mythos 5.2, with fewer cyber and biology blocks, is only for vetted organizations.
Why it matters
Anthropic's top public model just got cheaper and faster, and its own guidance is clear about when it's worth reaching for: long, ambiguous, multi-hour jobs where Opus 5.5 at high effort still falls short.
Who it's for
Developers and teams running long agent sessions, big migrations, deep research or hardware and science work in Claude Code or on the Claude Platform.
What it means for you
- In Claude Code (2.1.321 or later) or the Claude app, pick Fable 5.2 from the model picker; on the API use the model id claude-fable-5-2.
- Keep Opus 5.5 as your daily driver and switch to Fable 5.2 for the hard cases: a migration, a stubborn bug hunt, or a multi-hour research task.
- Try lowering effort before switching models; Anthropic says Fable 5.2 at High effort matches Opus 5.5's best FrontierCode score for about half the cost per task.
- Watch Settings > Usage: Fable burns through plan limits faster than other Claude models.
Applies to: Available November 9, 2026 in Claude apps, Claude Code and the Claude Platform (model id claude-fable-5-2), plus AWS, Google Cloud and Microsoft Azure. API price $8/$40 per million input/output tokens; optional fast mode (up to 2.5x faster) costs $16/$80. Fable runs inside Max and Ultra limits; Pro and Team standard seats normally pay with usage credits (free for one launch week, see the launch offer). Mythos 5.2 is limited to Anthropic's Cyber and Life Sciences Verification Programs. Checked on anthropic.com on November 10, 2026.
Related
Source: @Anthropic on www.anthropic.com ↗
Written by AgentStackList from the original post. Checked Nov 10, 2026. Features, plans and availability can change, so confirm on the source before you rely on it.
fable-5-2claude-codeanthropicmodel-launchpricing
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