In California, at least, Waymo is required to have $5 million in liability insurance. And the state has a law holding the manufacturer responsible in lieu of a driver. Though this setup has barely been tested since there have been so few incidents and the only "major" one (in CA) is still in court.

> Legally, who is liable for a self-driving car which makes a mistake?

Waymo? How is this ambiguous. Waymo makes the car, writes the software and operates the vehicle.

The only option is the owner of the vehicle, who would hopefully have insurance like any other vehicle owner.