There has been some discussion on this mailing list about the memory use of PEP 563 vs PEP 649.
It doesn't matter.
The memory use of either is small, and any measurements are merely measuring artifacts of the current implementations, and the current on-disk representation of code objects. In an ideal implementation, of either PEP, the underlying data for `__annotations__` will sit on disk at zero cost in memory and load time.
There are much more important differences between the two PEPs.
I support keeping the 3.9 behavior for 3.10 to give us time to resolve the discussion and maybe for us to implement some of the above "ideal implementation".