McLaren is a bit nuts, but in a good way. When most of us look at the MP4-12C, we see a damn near perfect car. When the engineers from McLaren look at it, they see potential for improvement. Previously, this has manifested itself in yearly upgrades, but now it's leading to a track-only variant.
The McLaren MP4-12C GT Sprint is inspired by the GT3 and Can-Am racing models, and features much of the same aerodynamic and cooling upgrades as those two cars, as well as a lowered ride height, chassis tuning similar to that of the GT racer, and Pirelli racing slicks. Basically, it's a GT car that's a bit more forgiving for amateur drivers who have no intention of actually racing, but want to spend "below GBP ÂŁ200,000" on an amazing toy.
There is one way in which the GT Sprint is just hands-down better than the GT3, though: air conditioning. The GT Sprint comes with a lightweight A/C system, and that makes all the difference.