I've often seen people say things like "I can't use TypeGuard yet, I'm stuck on 3.9". That's not true, because the typing_extensions package backports all typing features to all supported Python versions.

To help make people aware of this option, we should mention typing_extensions in https://docs.python.org/3.10/library/typing.html.

Perhaps this can go in the "Relevant PEPs" section, or at the end of the intro section.

Suggested wording:

"New features have been added to the typing module in each major version of Python. The typing extensions (link to GitHub) package provides backports to all supported versions of Python 3 for almost all of these features."