Claude Fable 5.1 is the default Fable model — in Claude Code, on the API, and in Copilot.
Claude Code v2.1.257 adds claude-fable-5-1 as the default Fable model: 1M context, $10/$50 per MTok, cache reads $0.25/MTok.1 v2.1.258 (npm latest) fixes a macOS 12 launch regression from 2.1.255 and remote/scheduled sessions dying after a re-sent permission approval.23
GitHub Copilot makes Fable 5.1 GA for Pro+/Max/Business/Enterprise; Business/Enterprise admins must enable the policy (off by default). Unlike other Claude models in Copilot, Fable 5.1 retains prompts and outputs for safety classifiers by default; eligible enterprises can get ZDR through year-end.4 Anthropic's platform notes dated 1 Sep match the same price and 1M window across API, Bedrock, Vertex, and Foundry.5
Pin Claude Code ≥2.1.258. Try Fable 5.1 for long agent runs; on Copilot, read the retention policy before enabling org-wide.