Launched officially at the 2017 Auto Shanghai on Wednesday, the car's vital statistics -- 460hp, 0-100km/h in 3.9 seconds, 174mph (280 km/h) top speed -- means it slots into the range above the standard M4 and the Competition Package M4 but below the now sold-out collector's edition M4 GTS.
But to make it fit into the range in that particular position, BMW hasn't simply re-chipped the engine and added some more aggressive aerodynamics. The car uses the same straight-six, three-liter block found in all M cars. And while it has some clever engine technology such as variable valve and variable camshaft timing, and charge air cooling for the twin turbos, much of the added performance is down to good old-fashioned weight-saving measures.
"This car breaks the '4-second-barrier' -- needing just 3.9 seconds from naught to a hundred [km/h]. To reach that speed, lightweight construction was essential: many parts are made from carbon fiber," said BMW's global head of sales and branding Dr. Ian Robertson.
This is why there is also prodigious use of forged aluminum, particularly for suspension components, and why the hood and roof are made from carbon fiber-reinforced plastic.
However, the company has drawn the line when it comes to the cabin. The door panels may be made from compacted natural fibers and boast a woolen rather than metal pull-handle, but BMW didn't want to sacrifice too much else in the way of everyday creature comforts.
So there's climate control, a premium sound system tuned to cope with the extra engine noise this car will make, and generous levels of leather and Alcantara trim, even if much of it adorns lightweight carbon fiber racing seats.
All of these touches, plus the fact that it sits on specially designed light-alloy wheels wrapped in Michelin Pilot Sport Cup 2 tires as standard (they're semi-slick but 100% road legal), also mean that the M4 CS can lap the Nurburgring in seven minutes and 38 seconds.
In other words, this is as fast as the M4 can go, before it stops being a road legal car and becomes a dedicated racer. What's more, it also means that the next generation of M cars, from the M2 to the M6 are set to get the CS treatment, too.