As much as I would like this to be true, I think it's not there yet (pre-FSD Beta 9, anyway).
I just took a 2-day road trip with Navigate on AP on pretty much the whole time. There were some wrinkles. It liked to declare its intention to change lanes, put the blinker on, and wait waaaay too long to execute. Several times I'd be watching a car approaching at like +10mph in the lane it was going to change into, and it would cheerfully wait until the car was nearly caught up and then try to cut it off. Another wrinkle was when it would be coming up behind a truck at like +1mph, with a car approaching in the left lane at +5mph or more, and it would try to execute the lane change waaaay before it caught up to the truck, thereby forcing the approach car to slow way down and wait a really long time for it to execute the pass and change lanes. Then, it seemed like maybe 1 in 10 times it should have changed lanes, it just wouldn't decide to. If I put on the blinker then it would change, and subsequent changes worked fine. I never figured out whether there were particular circumstances that caused it to not try to change lanes (passing lane clear, -1mph to -5mph compared to vehicle in front...) One time I guess the sun made the dashed lane lines look solid due to a strip of tar where they had joined two paving strips. Only once in the whole two days did it start a lane change and then abort, and maybe two of three times it braked for poor reasons (thinking a truck was coming into its lane when it wasn't, or seeing traffic in a merging on-ramp and braking even though the ramp lane was still 10 feet away from the rest of the highway). Once I intervened to avoid a cone... there was a coned-off lane which it respected, except the cones were placed 6-12 inches into our travel lane, and when one was more like 18-24 inches into the lane, it looked like we were going to clip it. Also, I guess, once it followed some cones that resulting in us driving half in a lane and half on the shoulder, but the lane-departure warning went bananas so while we were driving the right place it was like having a screaming toddler in the car.
Bottom line, I was still happy to have it compared to the incessant beeping of lane changes with AP but without Navigate on AP... but it still has a lot of room for improvement to reach zero interventions on a day-long highway drive.
I look forward to the FSD Beta 9 logic getting merged in to the regular Navigate on AP operation.