The AI is not quick to yield techs in my experience. Even if you’re beating them badly, it can take quite a bit of knocking around before they’ll start to relinquish them. This varies by AI of course. Typically, you can nab a few techs as you capitulate an AI. I can’t see plainly extorting techs is something I’ve seen work. You can extort 1 gold for a peace treaty, but this only works if the power ratio is heavily in your favor.