The current csv.pyi stubs import Reader like this:

if sys.version_info >= (3, 10):
    from _csv import Reader, Writer
else:
    from _csv import _reader as Reader, _writer as Writer

For Python 3.10 as it is not re-exported via as Reader or included in __all__ pyright and mypy do not recognize it as a member of csv and will complain when csv.Reader is used that csv has no member Reader.