To qualify for any federal EV
To qualify for any federal EV tax incentives you need to have at least 4kWh capacity battery driving the wheels, and that minimal size will get you a $2500 payback. Every kWh above 5 kWh qualifies for an additional $417, and the maximum a vehicle can receive is $7,500. So the RAV4 Prime will max out the EV incentive savings. State EV incentives are more complex and vary wildly between states. I think that Toyota marketing was again being conservative. 39 miles is significantly more than the Prius Prime's 25 miles EV range, but it is just an estimate, and 39 is a good number because if testing hits the high 30s in the real world then they are in the ballpark, but if they manage anything over 39 miles, then 40+ miles will look like a resounding success.