Claude Mythos model releases

The restricted sibling of Claude Fable 5.1, announced Sep 1, 2026. It is the same underlying model as Fable 5.1 but ships with more permissive safeguards for vetted users, available only through Anthropic's trusted-access programs — the Cyber Verification Program (defensive security work) and the Life Sciences Verification Program (professional biology R&D, developed with the US government). Anthropic reports it has the strongest cyber capabilities of any model it has released (still within the lower risk tier of its Frontier Compliance Framework) and scores 60.9% on Terminal-Bench 4.0 (vs 55.8% for safeguarded Fable 5.1). Also powers Claude Security's codebase vulnerability scanning. Access is currently limited to a set of US organizations. Not publicly token-billed, so list pricing is not recorded.

The restricted sibling of Claude Fable 5, sharing the same underlying Mythos-class model with fewer safeguards for vetted defensive-security and research use. Anthropic disclosed Mythos Preview on April 7, 2026, upgraded approved Project Glasswing users to Mythos 5 on June 9, suspended access under a U.S. export-control directive on June 12, and restored limited access for approved U.S. organizations on July 1 while it continues expanding the trusted-access program.