Not surprisingly, Cruise is happy. Chief executive Dan Ammann said the money would help Cruise (and therefore GM) roll out driverless cars on a "massive scale." Cruise has raised $7.25 billion in the past year.

The team certainly has plenty of opportunities to spend its money. GM is doubling Cruise's staff, and there's plenty of opportunities for technological improvement. There's also competitive pressure to think about. Waymo is expanding its self-driving taxi project, and Ford is testing self-driving cars. Cruise may need the sheer abundance of cash to keep pace with its rivals, even with one of the world's largest car manufacturers on its side.