Most obviously, the chrome front grille has been removed, leaving a pair of unobstructed air channels leading straight to the radiator for boosted cooling properties. Contrasting red paint inside marks this mule out most obviously from the standard M8 and matches the brake calipers, air-intake surrounds and towing-eye covers.
There's also a substantial rear wing for improved downforce over the standard car, a prominent lower splitter at the front, bespoke wheel designs and what looks to be a carbonfibre centre roof section. The rear windows have made way for plastic, vented items, but it's not clear which components in the rear of the car are being cooled.
There's some speculation as to whether the prototype will enter production as a standalone model or if it is being used to test various aftermarket additions for the standard M8 Competition. In any case, the added bodywork elements hint at a power upgrade for the car's 4.4-litre twin-turbocharged V8, which would make it BMW's most powerful production car.
In its current most powerful guise, the Competition, the M8 produces 616bhp and 553lb ft and can accelerate from 0-62mph in just 3.2sec. It's beaten in terms of outright power by only the new M5 CS, which packs 626bhp and shaves 0.2secs off the 0-62mph sprint time.
BMW's M performance division will turn 50 next year, and this car's red-and-white livery (with a blue element potentially obscured by the testing camouflage) suggests that it could be being readied as a commemorative anniversary model.
More details should be announced in the coming months.