Last month, leaked images gave us a clear look at the upcoming 2021 BMW 5 Series facelift in all its glory before its official debut. Inevitably, the new 5 Series facelift will spawn an updated version of the high-performance BMW M5. In its range-topping Competition guise, the M5's 4.4-liter twin-turbo V8 produces 617 horsepower, making it one of the fastest sedans on the road.

This won't be the fastest version of the M5 for much longer, however, because BMW is cooking up a lighter, more track-focused CS version of the M5 to join the M2 CS, M3 CS, M4 CS.

While the last prototype we spied was based on the current-generation M5, this new prototype captured on video getting a workout at the Nurburgring appears to be based on the new facelift model and sports some of the styling changes seen on the leaked photos of the 5 Series facelift.

The M5 CS prototype is disguised with camouflage covering the front and rear fascias, but it will adopt the same sleeker redesigned headlights and taillights as the regular 5 Series facelift. The air intakes in the front bumper are noticeably larger than the current M5 Competition, giving the M5 CS a more aggressive appearance. Curiously, this M5 CS prototype is missing the trunk lid spoiler and carbon-fiber roof featured on CS versions of the M2, M3, and M4 and the previous undisguised M5 CS prototype, but it could be at an earlier stage of development.

Under the hood, the output of BMW's twin-turbo 4.4-liter V8 is expected to increase to 641 hp, which is 24 more hp than the M5 Competition. It could also get a small torque increase over the current M5 Competition, which has 553 lb-ft of torque. If that seems excessive for a sedan, future BMW M models will be even faster as BMW M boss Markus Flasch recently confirmed the performance division won't be limiting power outputs any time soon.

Since the BMW 5 Series facelift has already leaked, we're expecting it to break cover this summer but we'll probably have to wait longer for the updated M5 and new M5 CS to arrive.