The ActiveHybrid X6 features BMW's dual-mode hybrid technology mated to a twin-turbo V8 and a seven-speed automatic transmission.
The $90k gets a list of things that aren't standard on the X6 xDrive50i including Nappa leather seats, 20-inch wheels, rear view camera, soft close doors, power tailgate, 4-zone climate control, etc. If you want even more, there are extras like the active ventilating seat package, cold weather package, Rear seat entertainment system, etc. All of which would push the price even closer to $100k.
For this price you could also get the 555-hp X6 M, but I guess it's not quite as "green."