How are the 4th Gens holding up?

Gen 4 Prius Hybrid can develop a coolant leak in the heat exchanger in the exhaust system leading to hard to recognize coolant loss and eventual engine overheat and head gasket failure if not caught. Symptoms are low coolant in the reservoir, vapor/steam in the exhaust and poor cabin heat performance. Can't speak to Prime issues from experience, but it's a much more complicated animal than the Hybrid: Larger/heavier traction battery with on-board battery charger, extra drive modes, HVAC includes heat pump for battery-only operation, to name a few.

 

overall very good car. as fuelmiser mentions, potential heat exchanger problem. no recall, maybe a tsb, idk how widespread it is. some come here to ask about it, others here haven't had a problem.
you wouldn't want one where the coolant temp light came on, nut idk how you could tell.
other issues have more minor. glitchy infotainment screen constantly rebooting, melting steering wheel leather, high drain on the 12v, i'm sure there are other things i've forgotten, but overall a solid car.

 

Water pump is unlikely to last to 150,000 miles. Rear wiper is vulnerable to car wash rollers. Rear sail panels usually lose some of their paint. Front end and splash panels are prone to damage due to low ride height. (If the front of the hood seems to not be flush with the front fascia, it could be that the radiator support frame has been tweaked against a curb, forcing the hood latch out of position).

However, it’s a more refined and comfortable car than the Gen 3, and gets better fuel mileage. My 2016 usually averages over 60mpg combined city and highway. Sometimes over 70 in town.

 

No rear wiper on a prime - curved glass. Make sure to flush out that pass-through drain at the bottom of the glass - during a car wash. Tends to get clogged up and causing intermittent seepage into the trunk area.
It is a very low ride and I always stop short of the parking blocks. Any rebar poking up from those blocks will rip out your plastic under-body. I've already had to replace a plastic fender liner; because the front portion got ripped out. $70 part and 10 minute fix. Some people simply drill some holes and zip-tie it back together.
Mechanically; no issues - though the informatics system did reset once on me while in-route somewhere.

Hope this helps....