Spotted for the first time undergoing testing in Germany, this X4 is tipped to be the next addition to the M Performance line that's already given us near-boiling models like the M135i and M235i on the one hand and the diesel-powered M550d, X5 M50d and X6 M50d on the other. Power in this case is tipped to come from the same 3.0-liter turbo six as the upcoming M2, producing between 360 and 380 horsepower.
Unlike the current top-of-that-specific-line X4 35i, which has two tailpipes on one side, this partially-camouflaged prototype has one pipe protruding from each corner of the rear bumper, but looks like it could easily accommodate twin pipes on both sides. Expect commensurate suspension, brake, rolling stock, aero and trim upgrades to come as part of the package, though they likely won't be quite as substantial as those applied to the X5 M and X6 M.
Sources expect the X4 M40i (or whatever it's ultimately called) to debut at the Frankfurt Motor Show in September 2015 before production gets underway in December.