I use python3 in production. Working at large bank.
If there's anyone not using python3 in production now, I'd be wary of that team. Maybe it could be forgiven two years ago, but now... There's just too much to be gained with modern python.
But hey, there's still some organisations using php3 in production!
I'd imagine the majority of teams are using python2 in production. Especially when LTS OSs ship with python 2.7. Things like Anaconda make it a lot easier to install python3 along side of python2.7 and move individual projects to 3.