Anthropic Adds Context Lock to Claude's Encrypted Reasoning

Anthropic has added a "context lock" to Claude's encrypted hidden reasoning. According to Odaily, encrypted reasoning generated by Claude 5.1 through the API must remain consistent with the system prompt, tools, and conversation history used at the time of generation, and the reasoning becomes invalid if the context is changed. The mechanism is mainly intended to prevent model distillation attacks. It further binds the reasoning to the specific conversation context, closing a path that could previously be used to extract the reasoning process by modifying the context.