Having had a few months experience driving a Tesla, and another Tesla  and Ac Chevy Bolt driven by a other family members, I suspect the OS is a variant of Android, highly customized of course to the task at hand.  One of the features with all-electric cars is that they are inherently simpler and thus require less maintenance, and have fewer failure points.  It also appears they have made basic tasks like steering and braking such that you have manual control if the CPU goes to sleep, you still have manual control.  Rotate the tires every 10K and that's about it.  And the software is updated regularly - sometimes it works better, sometimes not. 

The biggest issue seems to be the limited range, requiring more frequent charging.  You do not want to run the battery completly flat, as that can leave you stranded and at the mercies of a towing company, or Tesla if that's the car you drive.  However I managed a recent 2600 mile road trip with no excitement, and am planning a few more in the year ahead.