Simon Willison’s Weblog

We’ve seen the strong reactions to 4o responses and want to explain what is happening.

We’ve started testing a new safety routing system in ChatGPT.

As we previously mentioned, when conversations touch on sensitive and emotional topics the system may switch mid-chat to a reasoning model or GPT-5 designed to handle these contexts with extra care. This is similar to how we route conversations that require extra thinking to our reasoning models; our goal is to always deliver answers aligned with our Model Spec.

Routing happens on a per-message basis; switching from the default model happens on a temporary basis. ChatGPT will tell you which model is active when asked.

— Nick Turley, Head of ChatGPT, OpenAI