Anthropic Releases Official Prompting Guide for Claude Fable 5.1

Anthropic has published an official prompting guide for Claude Fable 5.1 and Mythos 5.1, detailing 15 behavioral differences from prior models across effort levels, tool-call batching, conversation history, writing style, and formatting, with corrective prompts for each. The guide notes many old prompts merely accommodated legacy model quirks.

2026-09-02 ~ 2026-09-02 · 3 related posts

• Claude releases Fable 5.1 prompting guide and API skill updates — ClaudeDevs · 2026-09-02
• Anthropic's Claude Fable 5.1 prompting guide: 15 behavior changes with fix prompts — AGI Hunt · 2026-09-02
• Anthropic releases official prompting guide for Claude 5.1 — ethanCaballero · 2026-09-02