Python 3
QIS v3.0.0 is a port of QIS v2.7 to run on Python 3.4 and above only. It contains a few tidy-ups, slightly better performance (around 10%) thanks to improvements in Python 3, but otherwise no major new features.
To upgrade an existing installation please follow the upgrading guide. For new installations see the install guide and Docker images.
The v2.x code (which supports Python 2.6 and 2.7), documentation and build scripts, can be found in the v2 branch but is not likely to receive any new features.