It only takes a few minutes behind the wheel to put to rest any worry that the complicated powertrain might muddy the GLC's performance. There's a lot going on underneath the skin, but for the most part the powertrain is seamless in practice. There are quite a few drive modes, including Comfort, Electric and three performance modes (Sport, Sport+ and Race) that all adjust things like throttle response, stability control, suspension tuning and steering effort. Electric mode is pretty self-explanatory; the GLC will keep the gas engine off and run solely on the electric motor. Comfort (the standard setting) is basically a "hybrid" setting that will fire the engine on and off based on a variety of parameters. The three sport settings keep the gas engine on all of the time, which has the added benefit of recharging the GLC's battery. No matter what setting you're in, if you floor the accelerator the GLC will give you everything it's got. That said, if you're in Electric or Comfort, it takes about a second for the gas engine to fire up and give you the power you want, though there's plenty on tap when it becomes available.
Acceleration is smooth and even, and you never feel any weird handoff between power supplied by the electric motor and that of the combined gas/electric powertrain. This is great, because plug-ins can feel sluggish if you're not using the gas engine. For example, the new Toyota Prius Prime sprinted from 0 to 60 mph at the Edmunds test track in 6.9 seconds; using only the electric motor dropped that time to 10.8 seconds. That's not the case here. While it's certainly not as quick as running in one of the hybrid modes, there's decent power (201 hp and 236 lb-ft) for city driving or passing on the highway when using just the electric motor.
We haven't had a chance to test it yet, but Mercedes quotes a 0-60 mph time of 3.4 seconds, a hair better than the 3.5 seconds we clocked in the old V8-powered GLC 63 S. That's not much of an improvement given the significant jump in horsepower (the previous version made 503 horsepower), but the extra oomph is likely offset a bit by the new model's presumed weight gain. Mercedes hasn't listed final specs, but given the additional equipment that comes (like that 6.1-kWh battery), we expect the 2025 model to be heavier than before.
That's not to say it feels fat or overweight. There's more than enough power for day-to-day driving, and you'd need a long and open stretch of road to really utilize everything the new GLC 63 S has to offer. The transmission is smooth most of the time yet can crack off upshifts extremely quickly when in one of the sport modes. The paddles are responsive and offer more driver engagement, but the transmission tuning is smart enough in automatic to generally have you in the right gear at the right time.
Handling is solid, too, and AMG's engineers have done a good job of masking the GLC 63's weight. Adaptive dampers are standard and adjust the suspension's responsiveness based on the road conditions and drive mode. Competitors like the BMW X3 M Competition are stiff enough to warrant a dose of ibuprofen after a few hours behind the wheel on anything less than perfect pavement. Not so in the GLC, though the ride does firm up a lot in the Sport+ or Race drive modes. The optional active roll stabilization uses multi-piece anti-sway bars both front and rear rather than solid one-piece anti-sway bars found in most vehicles. This means the car can decouple the anti-sway from left to right if needed, improving comfort without hurting performance.
Body roll is mild in corners, though the GLC does lean more than a sedan like the C 63 S. Same goes for brake dive, which is minimal but more than what we'd see in a sport sedan. The brakes are a bit of a mixed bag. While there's no shortage of stopping power, the pedal feels stiff and requires a bit more effort to slow the car than you might expect, especially when rolling up to a light or stop sign. You get used to the feel pretty quickly, but our preference would be for a bit more bite when you hit the pedal. Another minor issue is the available one-pedal driving function. There are four settings, including fully off, though none are particularly aggressive or will slow you to a complete stop. In our opinion, it's better to just drive it without one-pedal on. While they weren't on our test vehicle and won't be available by the time the GLC 63 S launches next year, carbon-ceramic brakes will eventually be on the options list.
Rear-axle steering is standard, and like most other rear-axle systems it works two ways. At speeds up to 62 mph (100 kph), the rear wheels turn a few degrees in the opposite direction of the front. That tightens the turning radius to make it easier to park and take a tight line through a corner. Beyond that, the rear wheels move in turn with the front wheels to increase high-speed stability. Early rear-axle systems could feel artificial and make handling a little unpredictable at times, but AMG has done a good job of making it seamless. The GLC turns in a little quicker than you might expect, but it's not unnatural and it mostly just helps make the vehicle feel more responsive. The steering helps, too. It doesn't offer a ton in the way of feedback, but the steering effort is spot on and the ratio quick but not darty.
The GLC 63 S is a lot of fun on a winding road, though anything particularly tight doesn't give you enough leash to really show off what the car can do. You need a lot of room to stretch its legs, though it's plenty capable in most situations. And while we love the power and performance from the new engine, the exhaust note is dull compared to the old V8's song.