One of our readers spotted something a little odd on a California highway yesterday. At first glance it looked like a F10 5er completely covered in camflauge cladding. But why? The F10 is already out and we know it ‘s not the M5 (due to the number of tailpipes alone). So we dug a little deeper and took a closer look. From what we can tell it ‘s one of several things.

– The mystery 5er could be the ActiveHybrid 5 that BMW showed off in concept form last year in Geneva. The timing would be right and the testing in the US would be crucial.
– Another option is that it could be a 535is sport model testing with an upgraded N54 or N55 (much like the 335is).
– Finally the third thing we think this car could be is the new turbo four cylinder that will replace the six cylinder in the 528 as the base model in the US. A four in the 5? With the higher power from the new four cylinders the engine would be pumping out the same power as the previous six while getting much better economy. (full gallery after the break)

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For the record we believe this is the ActiveHybrid but as always we ‘ll know more soon.