Update 2: We’ve got new info on the subject. Apparently this pack will only work with Razer’s “Hydra” motion controller, which is based on Sixense. The Motion Pack will be available at Portal 2’s launch, featuring completely new test chambers and testing elements. Sadly, it seems that the Antigravity Gun will not be in the base game, but perhaps some crafty modders will take the pack and get it to work on the PC. We’ve got our fingers crossed. We’ve got all this info, and some new gameplay, in a new video we’ve embedded (it’s the first one down there).

Update: Turns out there’s an entire booth dedicated to Portal 2 on the Sixense! Scroll down for the new videos.

Yet again, Valve sneaks up on everyone, this time to show Portal 2 at the Consumer Electronics Show in Las Vegas, running on Razer’s revolutionary Sixense motion control system, on the PC, with Intel’s new Sandy Bridge chipset, during the Intel keynote.

But just when you thought you weren’t gonna give a damn… Bam! Valve suddenly shows off a new functionality for the Portal Gun, the “Antigravity gun”!