alt Hacker NewsGood question. I find that GPT-5.5 thinking is very good at not thinking for simple questions, so much so that I've never had the need to use the instant model even for quick Q&A.
I'm assuming the instant model, then, is an entirely different smaller model mainly serving the free tier of ChatGPT.
It is an entirely free model, but it is also the model that most users (even paid) interact with until the router pushes the thinking.