Claude Mythos 5.1
Anthropic's gated Fable 5.1 variant for cybersecurity and life-sciences research
Claude Mythos 5.1 shares the same underlying model as Claude Fable 5.1, released the same day, but ships with the guardrails loosened for a narrow set of dual-use tasks: vulnerability discovery, red teaming, drug discovery, and biodefense screening. Anthropic isn’t putting it in the regular API lineup: access goes only to organizations vetted through its trusted-access programs, and pricing matches Fable 5.1 at $10 per million input tokens and $50 per million output tokens.
The split reflects a problem Anthropic has been open about: a model good enough to find security holes or help with biological research is also good enough to misuse for the same ends. Mythos 5.1 is the company’s attempt to keep that capability available to defenders and researchers without handing it to everyone who signs up for an API key.