Back in 2016, BMW released a hardcore, track-oriented version of the M4 called the GTS. The production run was supposedly limited to 700 units, though some insiders believe more cars were built. Even so, the 493-horsepower GTS is the most powerful of the F8X cars, and commands a huge premium on the used market. Though the M4 GTS was seemingly the ultimate car in the F8X generation, BMW is now testing what appears to be an even more hardcore model on the infamous Nurburgring in Germany.

As our spy photos reveal, this test car has an even more extreme wing setup than the GTS with a track-oriented diffuser at the back. Up front, this test mule is even more aggressive than the GTS with a massive front spoiler with canards. BMW has also cut out some air vents above the front wheels and behind the front fenders to help manage airflow. The side sills are also massive, indicating that this car will manage the air quite well. There are no shots of the interior, though we can spot what appears to be a half roll cage, which was also found on the M4 GTS. We wouldn't be surprised if BMW also found a way to produce more power from the twin-turbo inline-six and remove weight.

The M4 GTS was a highly coveted car, but it looks like its time as the most hardcore M4 model may be over. This test mule could be our first look at the return of the CSL name, which would be big news for BMW fans.