I've been pondering why I didn't seem to have the new Android Auto on my phone despite seemingly having the version number that supports it.
I discovered that the secret to getting the new Android Auto on my phone was to go into the settings on AA (not through the car, you can't make setting changes in the car!) and toggle a switch to enable the new interface.
Its quite nice I think.
The only annoying thing is that when you get out of the car, the thing is still running on the handset and you have to exit car mode to get your phone back... I've read others talk about that bug, maybe its going to be fixed soon.