The 2021 Mercedes-AMG GLS 63 is powered by a 4.0-liter V-8 biturbo engine with 603 hp, a nine-speed automatic transmission and all-wheel drive. In a first for the performance variant, the three-row GLS 63 has an integrated EQ boost starter-generator, which combines a starter motor and an alternator in a single electric motor situated between the engine and transmission, Mercedes says. It provides an additional 21 hp and 184 pound-feet of torque. Here’s a roundup of snippets of GLS 63 reviews from the automotive media.

“It took me only a few pulse-quickening, temper-heating miles to realize that driving the GLS 63 AMG on the freeway is nothing but an exercise in frustration, so I headed for the serenity of my favorite canyon roads. I’ve driven enough high-end SUVs that I should no longer be amazed at their competence, but the GLS 63 turned my frustration to utter awe. It was like driving a sport sedan from a flybridge on the roof. Steering response is sharp. There is virtually no body roll. Acceleration and deceleration are heroic. And despite 23-inch wheels — that’s only an inch less than the ones fitted to semi-tricks — and tires so low in profile that one wonders where the air fits inside, the GLS 63 AMG’s ride remains steady and comfortable at all times.

“Occasionally, I’d feel a momentary smidge of something — an incongruous sensation of pitch or float — that reminded me that I was driving a seventeen-foot, three-ton SUV. But then it was over, gone so quickly I could easily convince myself I had imagined it.”

— Aaron Gold, Automobile

“On twisting California mountain roads, the GLS 63’s extra heft prevents the sprightlier corner attacks that the GLE seems to take on with enthusiasm. Driven with the same spiritedness as its smaller sibling, the GLS 63’s brakes — 15.7 x 1.5-inch discs and six-piston calipers in front, 14.6 x 1.3 inch with single-piston calipers out back — start to emit the acrid scent of overcooked pads. However, on wider sweepers and expansive highways — you know, the kind of terrain the GLS 63 is most likely to traverse — its 123.4-inch wheelbase, longer by 5.5 inches, makes it feel more planted.”

— Ben Hsu, Autoblog

“There’s a heft to it you feel when you’re behind the wheel, a luxurious weight that gives you the impression you could smash through a brick wall, level a city block or cruise through a minefield, setting off the triggers without nary a scratch inflicted on its precious paint. It’s a tank. A fast tank.

“Steering is direct, though entirely numb. There isn’t a solution to this without the steering becoming semi-truck-heavy and turning off would-be buyers.”

— Jonathon Klein, The Drive

“With its 603 horsepower and 627 lb-ft of torque, the 2021 Mercedes-AMG GLE 63 S is an accelerative beast. It can hit 60 mph in a scant 4.1 seconds and reach an electronically limited top speed of 174 mph. Impressive, no doubt, but this power and performance don’t mean the GLS 63 is cantankerous around town.

“On the contrary, the GLS 63 is a refined sweetheart of an SUV, easy in the daily grind and boasting all the practicality of a standard GLS 450. The automatic restarts of the fuel-saving stop/start system are almost unnoticeable, and six driving modes (Comfort, Sport, Sport +, Individual, Trail and Sand) allow the driver to configure the GLS as desired. In each, this big Mercedes SUV impresses, aided by natural-effort steering and brakes. The engine pulls with authority all the way up to its 7,000-rpm redline.

“While comfortable on the highway, especially in Comfort mode, the GLS 63 belies its size on curvy mountain roads. The Sport model lowers the GLS by 0.4 inches, and body roll is practically eliminated by the standard Active Ride Control. Moreover, the rear-biased power delivery and standard limited-slip rear differential give this large SUV a truly sporty feel. Powering out of turns in a 3-row SUV has never felt this good.”

— Andy Bornhop, Kelley Blue Book

“Handling? Sure, the 2021 Mercedes-AMG GLS 63 handles. The air suspension can be turned to Sport or Sport+, and the 48-volt system powers the active anti-roll bars, which use a planetary gear set to keep the monster truck (mostly) flat through corners. Plus, the grip from the massive 285/40/ZR23 front, 325/35/ZR23 rear Michelin Pilot Sport 4s is frankly ridiculous. Are three tons of off-roadable (there are both Trail and Sand modes), Alabama-built, German fun happy getting whipped around the backroads of Malibu? No, but the capability is there. Plus, knowing you can pass any Prius at any time over any double yellow, well, that’s a bit more than half the point, isn’t it? Put another way, the Mercedes-AMG GLS 63 feels like a classic AMG, much more like that E 55 than, say, a GT R. Power first, power foremost, power forever, baby. Handling is for Porsches.”

—Jonny Lieberman, Motor Trend

“Our biggest concern with the GLS is the combination of speed and agility in a vehicle with so much mass. After just an hour behind the wheel, we found ourselves pushing harder and harder through the canyons. Our confidence was swelling, until we hit a mound in the pavement and the GLS started to understeer. It was neither bad nor dangerous — an easily correctable event caused by our failure to spot an imperfection on the road. Put us in that situation 100 times and we’ll come out okay 99 of them. But it did get us thinking.

“A vehicle with this much power and agility is already a lot to handle. Take its mass into account, and we worry that owners may not understand just how much momentum this three-row can generate. The reality is that, more than an E63 or an AMG GT, exercising the GLS 63 requires respect for its abilities. You can chuck any of those cars into a corner hard, but the physics at work in the GLS are a lot harder to cope with. Sir Isaac Newton has been dead for nearly 300 years, but his three laws of motion can and will bite anyone foolish enough to flout them.”

— Brandon Turkus, Motor1.com