This GitHub repo is used for three separate things:
The issue tracker is used to discuss PEP-level type system issues. However, typing-sig is more appropriate these days.
A backport of the typing module for older Python versions (2.7 and 3.4) is maintained here. Note that the canonical source lives upstream in the CPython repo.
The typing_extensions module lives here.
See CONTRIBUTING.md for more.
The typing.py module and its unittests are edited in the src subdirectory of this repo. The python2 subdirectory contains the Python 2 backport.