Cycle-trailing Yoga release (will happen during the Z development cycle)
Cycle-trailing Zed release (will happen during the AA development cycle)
Cycle-trailing Xena release (will happen during the Y development cycle).
Cycle-trailing Wallaby release (will happen during the X development cycle).
Victoria development
Ussuri - supports only Python 3.6 and greater
Train - last series to support Python 2
Stein. This isn't really a "series", there is no stable/stein branch.