Anthropic model with markedly improved safety alignment, including sandbox-escape resistance.
Anthropic launched Claude Fable 5.2 and Claude Mythos 5.2, targeting the hardest technical challenges with gains in coding, reasoning and vision. Fable 5.2 scored 41.3% on the Remote Labor Index, roughly double Opus 5.5 and GPT-6 Astra, and 1,000 Fable 5.2 agents formalized Fermat's Last Theorem in 30 hours versus 11 days for Anthropic's first formalization. Mythos 5.2 also cut sandbox-escape rates to 3.1% from 39% in Mythos 5.
Anthropic has upgraded Claude Fable and Claude Mythos to version 5.2, with gains in coding, reasoning and vision. Both share the same underlying model: Fable ships with cybersecurity and biology safeguards for general availability, while Mythos is gated behind verification programs for security and life-sciences organizations. In prerelease testing the models completed otherwise-infeasible software migrations, designed three working electronic devices from scratch, solved two open problems in black hole physics, and formalized Fermat's Last Theorem in 30 hours.