The current model has 577 horsepower, but its replacement could easily surpass the 600-hp mark.

[UPDATE, March 19] 12 new spy shots have been added at the beginning of the gallery, below.

It was only yesterday when the next-generation GLS was spotted roaming the streets of Germany and now our spies have sent us a batch of images with a more interesting prototype. Caught undergoing testing in a much colder environment, the fully camouflaged luxobarge had the now familiar disguise at the front grille in a grid pattern. That can only mean one thing: behind it was the menacing Panamericana grille reserved to the hottest AMG models.

This leads us to believe the test vehicle in question was the GLS 63 also taking into account it had bigger wheels backed by beefier tires. Yes, it did not have the typical AMG quad exhaust tips, but bear in mind this is an early prototype without all of the final bits and pieces. Another clue that could reveal the true identity of the large SUV is the bulging front and rear fenders as part of a more aggressive bodywork reserved for the performance-oriented GLS.

In regards to what will power it, our money is on a biturbo 4.0-liter V8 currently available in a plethora of AMG products. While the current GLS 63 has the old 5.5-liter V8 with 577 horsepower on tap, its replacement with the newer engine could have more than 600 hp. The engineers from Affalterbach have managed to extract a whopping 630 hp from the 4.0-liter unit for the new GT 4-Door Coupe, but it doesn’t necessarily mean the next GLS 63 will have the same amount of power. Nevertheless, a significant bump over the outgoing version is expected.

The next generation of the largest SUV from Mercedes will be faster not only thanks to its newly gained muscle, but also because it will switch to a different platform bringing a considerable weight loss. Needless to say, the diet will also pay dividends in terms of efficiency and should also free up more space inside the already cavernous cabin as a result of more optimized packaging.

Considering the regular GLS won’t be out until either the end of the year or early 2019, the spicy AMG-ified 63 derivative is not due to go on sale before 2020.

Photos: CarPix, Automedia

Gallery: New Mercedes-AMG GLS 63 spy photos