A quick primer on the now-industry-standard SAE International rules on how to discuss self-driving abilities: Level 0 is no automation whatsoever. Level 1 is partial assistance with certain aspects of driving, like lane keep assist or adaptive cruise control. Level 2 is a step up to systems that can take control of the vehicle in certain situations, like Tesla's Autopilot or Cadillac's Super Cruise, while still requiring the driver to pay attention.
Get past that and we enter the realm of speculation: Level 3 promises full computer control without supervision under defined conditions during a journey, Level 4 is start-to-finish autonomous tech limited only by virtual safeguards like a geofence, and Level 5 is the total hands-off, go literally anywhere at the push of a button experience where the vehicle might not even have physical controls.
If SAE makes a statement confirming or refuting that a L4 self-driving car has been achieved, this acts as the authoritative body. Failing that, a L4 self-driving car will be deemed commercially available when a relevant Wikipedia article (prioritizing the Self-driving car one if it still exists) says L4 self-driving car is commercially available for at least 6 months, 90% of the time (to compensate for troll edits). If Wikipedia stops existing, then a Metaculus moderator will resolve the question using their judgement.
More information on self-driving cars: Self-driving car — Wikipedia
- When will L3 autonomous vehicles be commercially available?
- When will L5 autonomous vehicles be commercially available?
[ETA 2020-11-19]: commercially available cars include vehicles used for ridesharing, robotaxis, etc.