We do know it's not all cars constantly, though. The PGE outage in San Francisco proved it, as anytime a Waymo came across a unpowered traffic light, it was configured to ask for assistance. This led to disaster, as there weren't close to enough humans to provide guidance to all the Waymos.
dwroberts|20 days ago
The way the cars behaved during the power outage could have been the result of anything - even eg. requiring full remote control and losing connectivity to a local facility