I wonder if then the __co_annotations__ call and overwriting of __annotations__ should be explicitly caused by a to get_type_hints instead of (mysteriously) occurring on an attempt to getattr __annotations__.

I would say: absolutely not.  While all "type hints" are annotations, not all annotations are "type hints".  As mentioned previously in this thread, typing.get_type_hints() is opinionated in ways that users of annotations may not want.  And personally I bristle at the idea of gating a language feature behind a library function.

Besides, most users will never know or care about __co_annotations__.  If you're not even aware that it exists, it's not mysterious ;-)

Cheers,

/arry