Anthropic releases Fable 5.1, updates API thought block handling

Icecream_monday · reddit · 2026-09-02

Anthropic has released Fable 5.1. A new support article details changes to the Messages API's thought block management, specifically designed to protect against model distillation.

Related event: Anthropic Releases Claude Fable 5.1 and Mythos 5.1(80 posts)→

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