Anthropic launches Claude Fable 5.2 and Mythos 5.2 models

Anthropic announced Claude Fable 5.2 and Claude Mythos 5.2 on November 9, 2026. The company says the models show gains in coding, reasoning and vision, and that they produce output faster than the 5.1 versions of Fable and Mythos.

Anthropic says Fable 5.2 handles difficult software engineering problems and can orchestrate agent teams and work on long-running projects. The model also solved two open theoretical physics problems, according to the company. During prerelease testing, Anthropic says the models helped its engineers complete software migrations that were otherwise infeasible and formalized the proof of Fermat's Last Theorem in 30 hours.

Claude Fable 5.2 is launching today. Claude Mythos 5.2 is limited to vetted organizations to start. The two 5.2 models follow the September release of Claude Fable 5.1 and Claude Mythos 5.1.

Developers building multi-agent systems can evaluate Fable 5.2 now for orchestrating agent teams and running long projects. Mythos 5.2 is not open to everyone yet, so teams without vetted access should not plan around it. The performance figures come from Anthropic's own prerelease testing, so check the model against your own workloads before switching.