If you use the API, you pay for a specific model, yes, but even then there are "workarounds" for them, such as someone else pointed out by reducing the amount of time they let it "think".

If you use the subscriptions, the terms specifically says that beyond the caps they can limit your "model and feature usage, at our discretion".

Old school Gemini used to do this. It was super obvious because mid day the model would go from stupid to completely brain dead. I have a screenshot of Google's FAQ on my PC from 2024-09-13 that says this (I took it to post to discord):

> How do I know which model Gemini is using in its responses?

> We believe in using the right model for the right task. We use various models at hand for specific tasks based on what we think will provide the best experience.