Waymo is already at level 4 at least on surface streets, and they claim 99.4% uptime in rain, high winds, and thunderstorms during last winter. [1] They're testing highway service in Phoenix now.
There might be a debate about the word "all" for the distinction between levels 4 and 5, but Waymo has six years to erase that doubt.
[1]: https://waymo.com/blog/2023/08/the-waymo-drivers-rapid-learn....
Level 5 fully autonomous would mean the car is able to drive in icy and snowy conditions (adjusting how it drives based on traction), it would be able to respond to verbal commands from construction workers, and it would be able to detect when a hazard in the road prevents it from continuing, plan a new route, and detour.
There isn't much incentive for Waymo or its competitors to create level 5 autonomous cars when there is a plenty large market in places where there is good weather and good signal for an employee to tell the car what to do if necessary.
Here's how you can tell so that you don't get confused as easily in future. Level 3 cars can require the occupant to drive the vehicle, "When the feature requests: You must drive the car". Waymo even offers service to people who cannot drive whether that's legally (they aren't licensed) or physically (blind people can use Waymo but can't drive a car). They are simply not required to take over driving.
What does it mean exactly? Because this can mean everything really. I mean you could guide decision making process by "now press break, now reverse and...", is it still driving?
AFAIK, that's what L5 means.
By "major cities" we mean any of the top 10 most populous cities in the United States of America.