For the public facing consumer functionality I have Gemini Flash running on guardrails directed by a state machine that calls it statelessly everytime. For that, it's strictly locked to a version. I can't afford to suddenly get responses that the SM is not tuned for.

As for which model does the building... I'm not at all attached. Enough logic, and CI gates/tests live outside the whims of the LLM to be able to hotswap them any time.