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Claude Mythos 5.1

Fable 5.1 with the safety classifiers removed. You cannot simply buy it.

currentAnthropicVerified 2026-09-02

Gated

trusted access only

Specifications

Context1Msource · as of 2026-09-02
Input ($/Mtok)$10source · as of 2026-09-02
Output ($/Mtok)$50source · as of 2026-09-02
LicenceProprietary, gatedsource · as of 2026-09-02
Max output128Ksource · as of 2026-09-02
ParametersNot publishedsource · as of 2026-09-02
Released1 Sep 2026source · as of 2026-09-02
Model IDclaude-mythos-5-1source · as of 2026-09-02

Official links

Claude Mythos 5.1 model page

What matters

  • The same underlying model as Fable 5.1, at a different safeguard level
  • US organisations and individuals in Anthropic's trusted access programmes only
  • Safety classifiers and high-risk fallbacks removed for Project Glasswing participants

Best for vetted frontier research.

Compare with

All 5 side by side →

Claude Mythos 5.1 vs GPT-6 Astra →Claude Mythos 5.1 vs Claude Fable 5.1 →Claude Mythos 5.1 vs Claude Fable 5 →Claude Mythos 5.1 vs Claude Opus 5.5 →Claude Mythos 5.1 vs GPT-6.1 Sol →

Also in Language Models

GPT-6 Astra · OpenAIClaude Fable 5.1 · AnthropicClaude Fable 5 · AnthropicClaude Opus 5.5 · AnthropicGPT-6.1 Sol · OpenAI