Your Claude Opus 5.5 keeps quietly switching to Opus 4.8, and it's supposed to prevent a security leak

Ask Claude Opus 5.5 something that brushes against security, and the reply can come back from a different model. A notice appears, the answer gets tagged Opus 4.8, and Anthropic's newest flagship stays switched to the older model for the rest of the chat. It's one of the safeguards Anthropic added so a model this strong at cybersecurity doesn't turn Claude into a security risk. A classifier flags the request, and Opus 4.8 takes over. The catch is in Anthropic's own system cards. In its prompt-injection tests, most of the attacks that got through came through that fallback model, not the flagship. Claude Opus 5.5 launched on September 22, and Anthropic rates its cyber skills close to Claude Mythos 5.1, the model it keeps behind trusted-access programs.

First reported by XDA Developers. This page is a short excerpt; the full text is theirs.