python 3.x

edit

See this ask.sagemath.org question - the FAQ needs to be updated, perhaps. But yes, it will eventually use Python 3.

Incidentally, since it doesn't use system Python, and since you can always from __future__ import ... something if you really need it, there's no need not to start using Sage now! Python 2.7 uses much of the new stuff optionally.

sage: print('5')
5

and the new string formatting stuff works

sage: '{0}, {1}, {2}'.format('a', 'b', 'c')
'a, b, c'

so what are you waiting for? (Only half-joking! Try it out!)