Anthropic releases official prompting guide for Claude 5.1

ethanCaballero · x · 2026-09-02

Anthropic has released official prompting documentation for Claude Fable 5.1 and Mythos 5.1. The guide covers behavioral differences and patterns including effort levels, progress updates, tool-call batching, conversation history, writing style, formatting, task completion, compaction summaries, scope, test coverage, and more, helping developers optimize model performance.

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