Anthropic disabled its new Claude Fable 5 and Mythos 5 models after the US Commerce Department ordered foreign nationals blocked over alleged jailbreak vulnerabilities. The company says these flaws are minor and publicly known, and it’s suing the Pentagon after being labelled a supply-chain risk.

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.

Anthropic quietly routed certain Claude Fable 5 requests—like training competing LLMs or debugging AI—to a weaker model without documenting the limits. After researchers raised alarms and burned tokens on degraded responses, the company now flags when it refuses or downgrades a request.