How efficient is the Audi A7's hybrid system?

I'm looking into buying a Audi A7, and I'm curious about its hybrid system. Can it fully run on electric power? How does the transition between gas and electric work?

The Audi A7's hybrid system is very efficient, able to reach speeds of up to 80 mph on electric power alone. The transition between gas and electric is seamless, with the gas engine kicking in only when needed.

I've been driving the Audi A7 for over a year now, and the hybrid system is one of my favorite features. It's able to save a lot of fuel in start-stop city traffic, and the switch between gas and electric is barely noticeable.