Public GitHub Capture Appears to Expose Claude Fable 5.1’s Expanded Runtime Prompt

A 269 KB file appeared on GitHub within hours of Claude Fable 5.1’s September 1 launch, presenting itself as a capture of the model’s runtime prompt. It offers a detailed view of how a production AI agent combines behavior rules, memory, search, safety policies and tool routing, but does not by itself establish a breach of Anthropic’s infrastructure.