urllib3 1.x has supported Python 2 for over 4 years since the end of Python 2's security release cycle. Since that time, download numbers indicate that Python 2 makes up around 2% of our total downloads across all versions.

Today it's quite difficult to actually test Python 2 on our 1.26.x branch due to dependencies and GitHub Actions moving on from Python 2 so long ago. I propose we update the minimum Python version on the 1.26.x branch to be "3" in the packaging metadata and remove any Python 2 CI/testing to avoid further blocking that branch. We won't intentionally break Python 2 support, but in the future a security fix may do so.

We'll also keep App Engine support around, but will be dropping the requirement to test it since it requires Python 2.