2021 Mercedes-Benz GLS-Class

The 2021 Mercedes-Benz GLS is Mercedes' large three-row luxury SUV. Mercedes redesigned it last year, and it's earned a top spot in our rankings because of its high levels of luxury, refinement and technology. Now Mercedes is expanding the GLS lineup with the performance-focused AMG GLS 63 S.

The AMG GLS comes in one flavor (for now), and that's the GLS 63. Like the more sedate 483-horsepower GLS 580 SUV, the 63 uses a twin-turbocharged V8 that also features a small 48-volt electric motor attached to the crankshaft.

This isn't a hybrid — there's no separate battery pack that can power the car alone. Rather the GLS uses a mild hybrid assist (Mercedes calls it "EQ Boost") that not only aids engine starting but also delivers a jolt of low-speed power when needed. The result is a rather absurd 603 horsepower and 627 lb-ft of torque put to the pavement through a nine-speed transmission and standard all-wheel-drive system. Other typical AMG touches also abound, such as a performance-oriented adaptive air suspension with advanced body-roll control.

Sure, there are plenty of luxury three-row SUVs out there. But few of them make 600 hp. The GLS offers a real, comfortable space for six or seven adults, making it ideal for growing families or driving partners at the firm out to lunch. Adding the AMG 63 trim just means that there's no ceiling to the expectations Mercedes buyers have of their SUVs … or how much they're willing to pay.

The GLS 63 has the lock on high-powered three-row SUVs. But there are a few close contenders. The Land Rover Range Rover Sport SVR cranks out up to 575 hp, but its third row is pretty small. The Tesla Model X has a roomy, adult-friendly third row and produces very quick acceleration from its all-electric powertrain, but it lacks the everyday versatility of most competitors.

There's also the oft-rumored but unconfirmed BMW X7 M, which could also easily adapt its twin-turbo V8 to seismic levels of power. Buyers simply looking for a blindingly fast SUV that can seat four or five passengers have several to choose from, including the Jaguar F-Pace SVR, the Porsche Cayenne Turbo or even the Lamborghini Urus.

Behind the wheel of the AMG GLS 63 S, it's a bit of a tale of two SUVs. On one hand, it can be a pleasantly accessible and easy-to-drive SUV. In its default Comfort drive mode, there's little hint of the performance potential or raw theater that comes with 603 horsepower. Flick the drive mode switch to engage the Sport mode and the 63 S' character changes abruptly.

The engine goes from sounding like a typical V6 to a high-performance V8, which is precisely what you'd expect from AMG. The suspension stiffens slightly to enable more athletic cornering and the throttle response sharpens. We won't say the GLS 63 S drives like a sports car, but it definitely deserves a bold "S" for SUV.

Mercedes says it'll reach 60 mph in a scant 4.1 seconds, which is ridiculously quick for a large three-row SUV. Handling is equally impressive, with body roll managed by the Active Ride Control suspension system that allows the GLS to corner much flatter. Even better, in the stiffest suspension setting, the ride quality remains composed and comfortable. It's not quite as smooth as the base GLS, but considering the gains in handling, it's a minor sacrifice.

We have but a few complaints with the 2021 AMG GLS 63 S. The transmission occasionally makes some uncharacteristically rough gear changes, and the lane-keeping assist system is far too sensitive and heavy-handed in its steering corrections when it tries to keep you in your lane. Thankfully, you can disable the lane-keeping system if you want.

The standard GLS interior is attractively designed and smartly engineered. The AMG GLS 63 S' cabin is essentially the same, though you do get an AMG steering wheel, premium Nappa leather, and sport front seats that have larger side bolsters to keep you in place when carving through turns.

One notable option is the Executive Rear Seat package that adds multicontour massaging second-row seats that are heated and ventilated. You also get a large center console between those seats that features a 7-inch MBUX infotainment display and a wireless charging pad.

Other options include a head-up display, enhanced navigation system functionality (it creates augmented reality directions on a front live-video camera image shown on one of the GLS' display screens), a premium Burmester surround-sound system, and various other aesthetic and comfort items.

In terms of transporting up to seven passengers, the GLS excels. It can even comfortably fit taller adults in the third-row seats. If you want to transport a lot of cargo, the GLS provides 84.7 cubic feet of capacity when you fold the second- and third-row seats down. That's more than what you get from Mercedes' GLE and about the same as from BMW's big X7 SUV.

Hauling both people and cargo is trickier. Luggage space behind the third rows is limited to a paltry 17.4 cubic feet, which means you probably won't have enough space for seven people and their stuff. If that's a regular occurrence for you, you might want to consider upsizing to an even larger SUV such as the Lincoln Navigator or new Cadillac Escalade.

The 2021 Mercedes-AMG GLS 63 combines the luxury, refinement and cutting-edge technology of the GLS class with rowdy German muscle. It promises performance, utility, a usable third row, and even off-road ability in a package with astonishing power.