Hey, thanks for the clear report and the step by step repro. This is a known bug on our side. In new chats, Cursor sometimes switches the selection to the recommended model (currently Grok 4.5) and turns on Fast, even if you turned it off manually. We’re tracking it, and the same case is being discussed here: Grok re-enables itself after being disabled in Settings
There isn’t a separate toggle to disable this behavior yet, so there isn’t a clean workaround. For now, in every new chat, reselect the model you want and double check that Fast is off in the picker before you send. The switch comes from the server side, so reinstalling or resetting settings won’t help.
I can’t share an ETA for a fix yet. Once there’s an update, I’ll post it in the thread.