So if one of my error messages leaks sensitive data to Sentry, and therefore gets used for AI training, are you going to delete your entire AI model upon request?

You know that technically that would virtually be the only guaranteed way to comply with such requests, right?

Sure, but if you unilaterally change the terms of that contract and don't re-consent for the expanded use, the old lawful basis doesn't really apply, now does it? I mean, whatever, the ICO will explain it to you soon enough with big legal words. Good luck!