The BMW M5 is already one of the fastest sedans on the market with its 600-horsepower 4.4-liter twin-turbo V8. But then BMW went an made an even faster M5 Competition model, which bumps the power up to 617 hp. The Competition models are the more extreme M cars for people who want a bit more speed but there is still one level in the BMW range above the Competition, the CS.

So far, we have seen CS versions of the M3 and M4 and BMW is currently working on an M2 CS, which is rumored to produce 450 hp. And the M2 CS will not be alone because our most recent spy shots prove that BMW is also testing an upcoming M5 CS. Get ready for an even faster M5 variant.

We spotted BMW testing a mystery M5 almost one year ago but now we finally have proof that it was the CS model. Unlike the car we saw last year, this prototype didn't appear to be wearing any camouflage as it drove off of a truck. BMW, shockingly, didn't even attempt to cover up the 'CS' badge on the trunk. The employees did try to block the CS from photos using a camouflaged facelifted M5 but the attempt was ultimately a failure. The CS appears to be based on the current M5, not the upcoming facelift, so the car might still be a year or so away from production.

Power figures remain a mystery but the CS is expected to produce even more power than the M5 Competition. BMW claims the Competition can hit 60 mph in 3.1 seconds, with real-world tests proving to be under three seconds. This new CS model should be even quicker and could come with a sub-three-second rating from the factory. We also love the gold wheels that will come mounted on the CS and we can't wait to see it in full production guise.