If this ends up half as good as the E46 CSL, it'll be a hit.
February 2016 marked the point that the BMW M4 hit its second birthday. Just six months after that milestone the Bavarians were caught lapping the Nurburgring with another M4 that looks a bit odd thanks to some carbon fiber jewelry. Luckily, our spy photographers managed to catch the modified version as it whipped around the track's bends and from we can tell it certainly isn't the facelifted model. If any predictions can be drawn from the massive rear wing it's that another special edition is on the way.
Previously we got the rare and expensive M4 GTS and later still an even rarer and more expensive (only 60 were made!) M4 CS that was only for Spain for some inexplicable reason. What's missing from this generation of the M4 that previous M3 coupes had are the CSL and GT4 models. By the looks of things one of those may soon be on the way. On this Bimmer the aerodynamic gear seems to have been dialed up to 11. Aside from the obvious large rear wing the aero upgrades seem to include a rear diffuser, new and more aggressive side skirts with air channels, and spoiler lips on the front lip and trunk. Interestingly enough, it seems that this M4 test mule is based off of the pre-face lifted version.
What this means is that development and testing started earlier. The car will look a bit different when it finally goes on sale. If this is the GT4 or the CSL (which stood for "Coupe Sport Lightweight") then we should expect healthy amounts of carbon fiber components, likely hidden from the camera, to complement the exposed carbon roof. It's hard to tell what's going on under that white paint, but we'd expect a CSL or GT4 to feature some suspension tweaks and an engine offering more than the standard 3.0-liter twin-turbo inline-six. Maybe not a water injection system like the GTS', but an increase in horsepower seems like an important addition to a special edition BMW. While the underbody fins smell like GT4 kit, let's hope it's the CSL to keep it road-legal.