Can you sleep in your Prius Prime and use the AC all night without using the engine?

Yes, if you keep it on READY mode, then until the traction battery runs out you can keep AC. Don't use the ACESSORY mode, you will drain the 12v battery very quickly. If the traction battery depletes, then the engine will come on.

 

Your 2021 Prime probably has the auto-shutoff feature, which will need to be disabled or it won't stay in "Ready" mode all night.

 

Is that a new feature in the 2021 model? I have not come across it in the manual, but now come to think of it there was a discussion about the "cabin mode" or something in Rav4 Prime.

 

even if you can disable the shutoff feature, a/c depletes the battery in less than an hour. then your engine is going to go on and off all night long.

 

The A/C is variable speed and power, over a big wide range: it can be over 2,000 watts running flat out, closer to 200 watts (a tenth!) at minimum speed, and at lower demand than that, it can cycle on and off. So the overnight temperature and humidity (and the climate setting) can make a big difference in how long the battery carries the load.