Having reported the 4 Series concept will make its world debut at the Detroit Auto Show just this week, our spies were quick to capture images of BMW's latest model almost completely uncovered, giving us a taste of what to expect when the covers are taken off the sleek coupe variant of the F30 3 Series sedan in January. Differences from the current 3 Series Coupe include a sleeker roofline and fastback tail, more elongated rear windows and a more angular Hofmeister kink.

A functional air vent can be seen on the front quarter panel and the side mirrors are shared with the sedan. Previous photos have shown the 4 Series' kidney grilles will be wider and sleeker than the new 3 Series, and that its headlights will be more svelte, reaching in to touch the grilles. This particular model is wearing 19-inch M Sport alloys and brake calipers, and from the looks of the exhaust system, is likely either the 435i or 440i. The 428i Coupe and Convertible will be powered by the same 2.0-liter twin-turbo inline-four as the 3 Series sedan, but the 435i (or 440i) may very well usher in the successor to the current N55 twin-turbo inline-six unit.

Both engines will be available with either a manual transmission or 8-speed automatic, and both should also be available with xDrive all-wheel traction. The 4 Series coupe (code-named F32) is expected to begin production in spring 2013, with the F33 convertible's production to follow later in the year.