This just showed up on my Facebook feed, from a friend with a Model S. He said he took this picture as he drove past the car in Palo Alto...
I think it is just a regular Model S with all the chrome bits, including the door handles, blacked out. the angle kind of hides the rear doors and angle of the lift gate.
Agree -- if you look closely, the window has a slightly different sheen on the forward half. Since they are roughly the same size, it indicates a regular Model S sedan… If it was a coupe, I'd expect the rear window to be not quite as long (and the front door/window to be longer…)
Model 3 confirmed! Edit: JUST KIDDING, relax. It's just the X being tested with all the camo removed finally... Turns out Bonnie was right all along. /s