Gen 4 Prius Prime mpge record: 280 mpge = 8.3 mi/kWh

I achieved a new Gen 4 Prius Prime mpge record last Sunday night on my grocery trip.

vehicle: blue 2021 Prius Prime Limited @ ~ 24,000 miles
outside temperature: 75 ℉
one-way distance: 7.6 mi
maximum cruising speed: ~ 25 mph (= 27 mph on the speedometer)
A/C use: none
fog lights: on
audio: on

mpge = 33.705 kWh/ge × mi/kWh

outbound-trip mpge: 280 mpge = 8.3 mi/kWh
round-trip mpge: 276 mpge = 8.2 mi/kWh

useable battery capacity: 33.705 kWh/ge × 25 mi / 133 mpge = 6.34 kWh

BEV range corresponding to the outbound mpge: 53 miles
BEV range corresponding to the round-trip mpge: 52 miles

Note that both legs were fairly flat, with minimal change in elevation—so, there is no cheating here. In practice, you can even have a negative mpge if you only drive downhill.