Anthropic has launched Claude Fable 5.2 and Claude Mythos 5.2, its new models built for the hardest technical work — coding, reaso

Fable 5.2 and Mythos 5.2 are the same underlying model in two tiers. Fable 5.2 is available to everyone, with strong cybersecurity and biology safeguards. Mythos 5.2 has those safeguards relaxed and is limited to vetted organisations through Anthropic's Cyber and Life Sciences Verification Programs.

The numbers: up to 30% faster output than Fable 5.1, and 20% cheaper — $8 per million input tokens and $40 per million output tokens, down from $10 and $50. An optional fast mode runs up to 2.5x faster at $16 per million input and $80 per million output tokens.

On Anthropic's FrontierCode 2.0 coding benchmark, Fable 5.2 scored 49.1% at Xhigh effort — up from 32.4% for Fable 5.1 and ahead of Opus 5.5 at 45.5%.

In pre-release testing, around 1,000 Fable 5.2 agents formalised Fermat's Last Theorem in Lean in just 30 hours, with minimal human intervention — the first formalisation took 11 days. The model also solved two open problems in black-hole theoretical physics, and one engineer had it build a working operating system in eight days, coordinating 1,000+ subagents around the clock.

Fable 5.2 is available on the Claude Platform (claude-fable-5-2), Claude apps and Claude Code, AWS, Google Cloud and Microsoft Foundry. Anthropic still recommends Opus 5.5 as the everyday starting model.