Chris Chin of The Drive gives a quick summary of the Society of Automotive Engineers' levels of autonomy for self-driving cars:

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.

When will these degrees of self-driving car autonomy be developed and commercially available?

The sub-questions below will resolve on the earliest date that SAE makes a statement that a commercially available$^†$ self-driving car meets the respective standard of autonomy. If no statement by SAE is available, statements by relevant car manufacturers, taxi service providers, and credible media reports will also be sufficient.

For this question, "commercially available" means that any member of the general public can purchase a car, rent a vehicle, or hail a ride-sharing or public transit vehicle. A service providing commercial delivery or freight would also be sufficient. Any availability of such services anywhere in the world is sufficient for this question.

$^†$ [ETA 2020-11-19]: commercially available cars include vehicles used for ridesharing, robotaxis, etc.