Anthropic introduced Claude Fable 5.1 and Claude Mythos 5.1 as the same underlying model with different safeguard stacks. Fable 5.1 is generally available for coding and hard knowledge work across Pro, Max, Team, Enterprise, the Claude API, and major clouds; Mythos 5.1 stays limited to trusted access programs with safeguards aimed at cybersecurity and life-sciences work.
Anthropic pitches the pair as its strongest models yet for long-running, multi-step jobs — the kind that stretch across hours, tools, and apps rather than a single chat turn. List pricing for Fable 5.1 is $10 per million input tokens and $50 per million output tokens, with US-only inference available at a 1.1× multiplier. The release is the clear AI-model headline of the week beside OpenAI’s Astra path, and it resets the “what’s the best coding agent” conversation overnight.
Source: https://www.anthropic.com/claude-fable-and-mythos-5-1