Our friends at ToyWorth.com first discovered this variant at the 2012 San Diego Comic Con.
This sample video shows the Knight Rider talking "KITT" base, compared to the variant talking "KARR" base. Mattel employee explained they had planned to pull these variants (due to the paint error on KARR, missing the silver underbody) but a few made it out for sale during the convention. It is basically a KITT car in a variant KARR package. Good luck hunting for the variant! Click through for the pictures and video!