A roughly 120,000-character system prompt for Anthropic’s Claude Fable 5 model has been leaked, revealing detailed behavior instructions, product information, refusal rules, and formatting guidelines. The prompt outlines how Claude should handle user requests, safety measures, available features, and external documentation searches.

Simon Willison breaks down the changes between Claude Opus 4.6 and 4.7’s system prompts, including the renaming of the developer platform, addition of a PowerPoint agent, expanded child safety and disordered‐eating rules, and a new acting_vs_clarifying section. He also notes Claude’s new tool_search mechanism, tighter verbosity controls, removal of certain style restrictions, and an updated knowledge cutoff.