As a matter of fact, is there any real advantage in having a 9, if I'm going to run GrapheneOS on it? I'm assuming whatever fancy new "AI chip" these things carry is not used with GrapheneOS? I know nothing about phones.

Yeah, having the latest Google Pixel 9 with GrapheneOS definitely gives you a different experience. The chip and camera are improved over the previous models, which can make a noticeable difference. But you're right—GrapheneOS lets you do everything you'd do on any other Android phone, with the bonus of enhanced security and privacy. The AI features are only available within the stock OS though.