Anthropic has introduced Claude Fable 5.1 for ambitious projects that can run for hours or span several applications. The company highlights repository-scale coding, deep research and document-heavy professional work.

Fable 5.1 costs $10 per million input tokens and $50 per million output tokens. Cache reads cost $0.25 per million tokens, which can lower the bill for agents that repeatedly reuse a large prompt or working context.

Claude Mythos 5.1 shares the underlying capabilities but is built for sensitive cybersecurity and life-science research. It is available only to vetted organizations, so most businesses and individual developers will be choosing between Fable, Opus, Sonnet and Haiku.

What this means

  • Fable 5.1 is Anthropic's top generally available model.
  • Lower cache-read pricing can help long agent sessions.
  • Mythos 5.1 remains a restricted model.

Read the announcement

We explained the update in plain English. Use the original source below for the full announcement and any later changes.

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