"1. Is my code, including prompts and answers, used to train Google's models?

This depends entirely on the type of auth method you use.

    Auth method 1: Yes. When you use your personal Google account, the Gemini Code Assist Privacy Notice for Individuals applies. Under this notice, your prompts, answers, and related code are collected and may be used to improve Google's products, which includes model training."

The opt out appear to be about other type of stats, no?