Why does the Audi A8 have a high fuel efficiency?

I've noticed that compared to other luxury cars, the Audi A8 has a relatively high fuel efficiency. Can you explain the technology or features that contribute to this?

The Audi A8 features a mild hybrid system that utilizes a lithium-ion battery to provide additional power and assist the engine. It also has a coasting function that disengages the engine when coasting at speeds between 55 and 160km/h, providing better fuel efficiency.