I've never had chatgpt ask me to upgrade, though it maybe because my context lengths are usually smaller. Usually popups also go away afternoon repeatedly rejecting them(it might be only a script).

But yes your chats do go Into its training data and chatgpt does keep getting at answering niche technical things, it's gotten so good with nostr as well.

Though I would still advocate for self hosted models and would be very careful about what I talk to chatgpt about.