Yikes. If I read this correctly, it could really screw up FastAPI. That would be a serious headache for me, in a way that’s far worse than the breakage I normally expect from a “3.9” -> “3.10” transition.
Could you explain what breakage points do you expect for FastAPI with those changes that may impact Pydantic?
FastAPI uses pydantic for data validation. By my read of this issue, if PEP 563 happens without PEP 649, the code I write will see data that’s not been validated the way I expect it to. If my code treats data that hasn’t been validated as if it has, I’m gonna have a bad time.