Late last year, former BMW M Division CEO Markus Flasch commented the new M4 CSL was an open secret. Numerous prototypes have been captured on camera, and in early January, BMW said a special edition model was coming later this year. Still, the CSL hasn't been officially acknowledged by BMW, and that remains the case.

However, new spy photos actually reveal CSL branding for the first time. An M4 test vehicle was caught at a fuelling station by a spy photographer who wasn't the least bit shy about getting up-close for a detailed look. When the driver opens the door, the camera zooms in on the aggressively bolstered seat that looks slightly different compared to the standard model. More carbon fibre is visible below the headrest, but look behind the seat. In plain view is a CSL logo, occupying space where you'd usually find a back seat. Yes, the CSL will ditch the rear seat in the name of weight savings.

2023 BMW M4 CSL Seats Spy Photo
2023 BMW M4 CSL Front View Spy Photo
2023 BMW M4 CSL Rear View Spy Photo

On the outside, we see the same level of camouflage wrap covering other prototypes but with the vehicle stopped, changes to the front and rear fascias are easy to spot. The CSL's chin spoiler is prominently featured here, not to mention the grille structure and vents in the lower bumper.

Gallery: 2023 BMW M4 CSL Up Close Spy Photos

At the rear, the spoiler literally stands above everything else, though the swirling wrap still makes it tough to spot changes in the taillights. The rear bumper with the quad exhausts looks similar to standard M4, but there could be some minor alterations to the diffuser.

When the CSL does become official, it could pack upwards of 550 bhp sent rearward via an eight-speed automatic. Combined with a weight reduction said to be over 100 kilograms, the return of the CSL should be performance dynamo both in a straight line and around corners. As for exactly when the debut will happen, a summertime event is likely.