I think it is on all X5s, check your manual or the pdf version on this site, around p. 98 or 99. It describes the adaptive brake feature and it is not listed with an * which would indicate optional equipment.

You could always just hang a big mirror on a wall and back-up real fast into it applying the brakes to see if the other lights come on. Just kidding.

Seriously though it looks like it is standard equipment on all models of the X5.