the new toyotas are according to the dealer "lifetime" but that is total BS. Lifetime to a dealer means warranty period. Not Lifetime.
I do my own, i purchase Denso WS fluid from Rock auto. OEM Manufacturer for the Toyota fluid. It really is not that difficult. I've assisted Colin on his 4runner and have done the RX400h and the Prius. key is raising the vehicle level. More difficult in the prius than the others as you can slide under the higher vehicles. it takes approx 4.2 quarts give or take what the spec is for your vehicle. There is no filter, only a drain and a fill plug. What i do, warm up the vehicle, bring it into the garage. Lift straight up and level. I actually purchased Quickjacks for my garage to do the prius transmission fluid. Key is a long clear tube to snake down the engine bay into the fill plug. Have a partner do the top part, you insure the hose is in the transmission, once it runs out, put the plug in it. after you drain and fill you can drive around, then recheck the fluid level. I did mine originally @ approx 120000 (was shooting for 100K but didn't get there) then every approx 60k. with the intent to line up transmission fluid swaps eventually at the 50k markers on the odometer around 150-200k. We put 20K on each vehicle per year so i do oil every 5k, wiper blades every fall etc.
These are not the old school transmissions with a pan you drop and swap the filter, reinstall the pan, and fill thru the transmission dip stick. No external hose to tap into to do a "flush" only way to "flush" is new fluid, run it, drain, new fluid again.. I am not that energetic. I can tell you that each vehicle we did change the fluid on was gross.. Even the little Prius had pretty gross fluid.
I cheat and reuse the old drain and fill gasket. I would imagine you are supposed to get new ones, i think you are supposed to get new drain plug gaskets as well but i reuse those for a while as well.. I do however change my drain plug on the oil to magnetic. I probably should change the trans drain plug to magnetic as well. Possible part #'s in picture attached.