A variant of the BMW M4 has been spotted testing on the Nürburgring. At first glance, it appears to be a regular M4 GTS – if the bewinged lightweight special could be considered “regular” – but look closely and you’ll find a whole host of tacked-on aerodynamic addenda.

Clear to see is a larger front splitter with endplates, along with front flics and a vented bonnet. There are also more prominent “Air Breather” vents aft of the front wheels, supported by another row of vents at the top of the fenders. Meanwhile, the side skirts are much deeper and are of a more elaborate design.

But it’s the rear of the car where BMW has really gone wild with the car, with a tall rear wing, a second bootlid spoiler and what appears to be a massive Formula 1-style double diffuser. This, then, is clearly a much more serious offering than even the GTS – and since the current F82 M4 is on its way out, it would make sense for Munich to produce a properly hardcore runout special.

Expect outputs from the 3.0 litre twin-turbocharged straight-six to exceed other variants in the M4 range, utilising technologies like the GTS’ water injection to push power beyond the 500 hp of the GTS. As for the name, we can’t say for sure what it would be called, but our spy photographers have floated out the legendary CSL name, which seems like a pretty good guess.