When Caddy says the ATS is "all new" they mean it. This isn't a new compact sedan concept shoehorned onto some existing platform. Ken Kelzer, Global Vehicle Chief Engineer for Cadillac told me they wanted a car that could deliver premium luxury and performance, but also be fuel efficient and lightweight. And no existing platform would be able to do that.
Forget the big, heavy, lumbering Caddys of yesteryear, the ATS is a car that's lighter than any of its competitors (the engineers were fanatical-they even used lighter, stronger bolts to shave weight), with a frame and body that use a variety of materials from aluminum to multiphase steel, to save weight without sacrificing strength. The goal was also to create a car with perfect 50/50, front to rear, balance to deliver driving performance that's track inspired.
I decided to test that balance on track, and while I was taking turns at a higher speed than you will (or should), the ATS stayed remarkably flat through the curves. (The optional Magnetic Ride Control included in the Premium edition I drove helped with that too. It's also a miracle worker for sucking up everyday bumps and potholes.)