On the web app, I see the "temporary chat" option but no toggle. It tells me temporary chats aren't used for model training. I thought I remembered that chats of Pro customers aren't used for that in any case. Hard to keep track of all this stuff.
Ultimately, I think the crossover memory is useful, but I'd really like to know exactly what's in there and an ability to validate/adjust, not just on/off.
Model training is completely different than keeping a summary of chats on the side and injecting it as context.
In my Gemini app, when k click new chat and click the filters button I have “Personalize Intelligence: Personalize chat when helpful.”
It is on every time I click new chat. Maybe you need to enable it in settings first. I can disable it to have a clean chat without personal context, but preserve the chat history unlike temporary chat.