It would overlap with M3.
BMW has not yet revealed the 4 Series Gran Coupe. However, the 2022 I4 it released last month is an indication of what we can expect. Rumours circulated that BMW might offer a fully-fledged M4 Gran Coupe. However, the company has now officially dispelled those rumors. Robert Pilsl, M3/M4 Project Manager, stated to BimmerToday the company does not require an M4 Gran Coupe at this time.
This is not surprising considering the way BMW has rearranged its lineup. BMW introduced the 4 Series Coupe, which replaced the 3 Series coupe and sedan, several years ago. BMW then added the rear doors to the 4 Series Coupe and called it Gran Coupe. This allows for some overlap in the lineup. The standard M3 would have a four-door M4 Gran Coupe.
Pilsl stated to the publication that the company will continue with its core M-brand models. This includes the M3 Touring wagon, which is a first for them. BMW announced the M3 (and M4) together last September, as they share a platform. The M3 and M4 share the same 3.0-lite inline-6 twin-turbocharged engine. It produces up to 503 horsepower (375kilowatts), and has an electronically limited top speed. An M3 four-door Gran Coupe M4 would have a different roofline.
BMW will instead focus on the M3 wagon, which will expand the M lineup in an entirely new direction. The M3 wagon won’t be available in the US, as BMW offers more attractive go-fast products for American shoppers. However, it gives the M lineup something that it hasn’t had before. The M3 Touring is more restricted than its M3 counterpart. Rumours suggest that the wagon will have an all-wheel drive and an 8-speed automatic gearbox. This is still a better option than a four-door M vehicle.