Anthropic releases two models: Claude Fable 5.1 and Claude Mythos 5.1.

Anthropic introduces the Claude Fable 5.1 and Claude Mythos 5.1 models, positioning them as "the world's most advanced programming and knowledge work models." Claude Fable 5.1 is available to all users, while Claude Mythos 5.1 is limited to review organizations. In terms of performance, Claude Fable 5.1 surpasses its predecessor and GPT-5.6 Sol in multiple benchmark tests, including Terminal-Bench-Science and CursorBench.