It has been in the works for several years and now the ultimate version of the BMW X7 has finally arrived. Introducing the 2021 BMW Alpina XB7: the fastest and most powerful version of the company's flagship SAV. The XB7 joins the B7 in Alpina's two-model lineup for the US market, taking all of the luxury and performance of the X7 and dialing it up several notches.

Power comes from the same 4.4-liter twin-turbo V8 found in the top variants of the X7 but Alpina's version has been fettled, so it now produces a whopping 612 horsepower and 590 lb-ft of torque. As always, the grunt goes out to an xDrive all-wheel-drive system through an eight-speed automatic transmission. BMW says 0-60 mph in the XB7 takes just 4.0 seconds and the top speed is 188 mph, which should come in handy for blasts on the unrestricted Autobahn.

In order to extract its own flavor of performance out of the X7, Alpina made unique changes to BMW's N63 V8 engine. The cooling system now features two additional external water coolers, an enlarged transmission oil cooler, and a low-temperature cooling system. Alpina even installed its own intercoolers because BMW's just weren't considered good enough. An Alpina sport exhaust system with active flaps is unique to the XB7, giving it a throatier sound.

The Alpina XB7 features an electronically-variable active limited-slip differential on the rear axle, which improves grip by applying torque to whichever wheel needs it most. We were already impressed by the ride comfort of the X7 but Alpina's tuning of the standard two-axle air suspension should be even more pillowy. The feeling of completing the quarter-mile in just 12.6 seconds while carrying up to seven people and 5,860 pounds of curb weight should be quite sensational.

Part of the appeal of buying an Alpina-branded BMW is its incredible wheel designs. As standard, the XB7 rides on 21-inch Alpina Dynamic wheels wrapped in 285/45R21 front and rear performance summer or all-season run-flat tires. Optionally, 23-inch forged-alloy wheels are available with the legendary 20-spoke Alpina Classic design. Even though these wheels are larger, their forged construction saves 28 pounds off the curb weight. Alpina will wrap these wheels in bespoke Pirelli summer tires (specific to the XB7) measuring 285/35ZR23 at the front and 325/3 ZR23 at the rear.

Bringing the XB7 to a halt are four-piston Bremo brakes at the front and floating brake calipers at the rear. All of the calipers are finished in Alpina Blue with Alpina White lettering. Other exterior changes include a unique front fascia with Alpina lettering and larger intakes and a unique rear bumper featuring quad exhaust tips.

Inside, Alpina hasn't messed too much with what is already a wonderful interior. The XB7's main competitor, the Mercedes-Maybach GLS 580 is strictly a four-seater but Alpina has opted to leave the X7's three rows of seats intact. As with the standard X7, buyers can select either a bench seat or two comfortable individual captain's chairs in the second row. Opting for the captain's chairs will make second-row occupants more comfortable but will cut the seating capacity from seven to six and limit the max cargo capacity from 90.4 to 48.6 cubic feet.

Since this is the highest trim level of the X7, the XB7 comes decadently equipped. Standard features include Merino leather, multi-contour seats, soft-close doors, Alcantara headliner, leather instrument panel, and a three-part panoramic glass sunroof. As an optional extra, BMW's lovely Panorama Sky Lounge LED roof is available.

Some Alpina-specific interior touches include a glass iDrive controller with a unique Alpina design, blue illuminated gear selector switch, Alpina production plaque, illuminated Alpina door sills, and the unique Alpina sport steering wheel hand-finished in Lavalina leather and blue/green stitching. Alpina's lovely myrtle luxury wood trim comes standard while piano lacquer and an all-new natural walnut anthracite trim are also available.

BMW says order books for the Alpina XB7 open in May 2020 with the first deliveries scheduled for September 2020. Pricing begins at $141,300 plus a $995 destination fee, making it over $40,000 more than the X7 M50i but likely much less expensive than the Mercedes-Maybach.