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Anthropic / current

Claude Fable 5.1

Anthropic's coding-specialised flagship, sharpened in the Fable 5.1 revision.

Context1M
ModalityText · Image
AccessAPI · Cloud
ReasoningAdaptive

Where it fits.

Built for demanding software engineering where sustained multi-step execution matters more than unit cost. Fable 5.1, released September 1, 2026 alongside Mythos 5.1, remains the coding-focused flagship even after the Opus 5.5 launch.

02

Core capabilities

  • 1M context and up to 128K output
  • Adaptive thinking with long coding sessions
  • Agentic coding, terminal work and tool use
  • Availability across Claude API and cloud partners
03

Best-fit workflows

  • Autonomous coding agents
  • Large-scale migrations
  • Debugging and repair loops
04 / OPERATIONS

From evaluation
to production.

Deployment notes

Reserve Fable for work where the model must hold a multi-hour coding thread together. Preserve thinking blocks, gate destructive actions behind explicit approval, and keep Opus 5.5 as the cheaper default.

Watch before choosing

Premium and slower than the 5.5 tiers; compare Opus 5.5 before paying the gap for routine work. Non-default sampling parameters remain restricted; relying on them can break portability.

05

Family & versions

Specifications and positioning checked against provider documentation.

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