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.

The entire source code for Anthropic’s Claude Code CLI has leaked due to an internal error during a package release. This includes nearly 2,000 TypeScript files and over 512,000 lines of code, exposing the application’s inner workings to competitors and developers. Anthropic has acknowledged the mistake and stated it was not a security breach.

Anthropic unintentionally exposed the source code for Claude Code, its AI product, through a public npm package. The leak, which includes sensitive architectural details, poses significant risks for users and gives competitors insights into its technology. Users are advised to take immediate security precautions due to potential vulnerabilities.

Anthropic has confirmed its most powerful AI model, Claude Mythos, after a configuration error exposed details about it. The model is said to significantly outpace previous versions in reasoning and cybersecurity, but it also poses serious risks, with the potential for misuse in cyberattacks. Early access will be limited to cybersecurity-focused organizations due to these concerns.