The GT4 spec is the lowest class of FIA GT racing. It's meant for amateur racers, and as such the regulations are quite strict. Every car must have at least one amateur driver, and the rules as to what constitutes as an amateur are very specific and clear. Aside from BMW, Aston Martin, Porsche, and Toyota all field cars in GT4 spec races.
Like the M3 GT4, the new version of the M4 comes from the factory homologated to FIA GT4 spec. BMW says the M4 GT4 will use the standard coupe's 425 horsepower twin-turbocharged 3.0-liter inline six cylinder engine, including the electronics – the outgoing M3 GT4 used the standard car's 420 hp, high-revving, 4.0-liter naturally-aspirated V8. The new car will also pull bits like a carbon fiber hood from the M4 GTS.
Specific details like weights or fluid capacities haven't been revealed, nor has the transmission been confirmed. It's unclear if the M4 will be heavier than the smaller outgoing M3, which weighed slightly over 3,000 lbs. Expect things like built-in air jacks, a roll cage, lightweight seats, and other race-ready parts to carry over.
The M4 GT4 will start testing at the end of 2016 in preparation for a 2018 debut. Customers with who can't wait can purchase one of BMW's other race-ready offerings. BMW currently sells the M6 GT3 and M235i Racing. Parts like the pedal box, brakes, and seats for the M4 GT4 are the same as those in the M6 GT3.
Pricing hasn't been announced, but the current M3 GT4 sells for about $140,000. The car should go on sale late next year.