Valve's VR reveal's been the big news at GDC this year, and one of the things it used to show off the tech was a short custom Portal demo apparently running in Source 2.
To be clear, this was just to demonstrate the tech and Valve has specifically told PC Gamer that this doesn't mean there's a Portal sequel in the works. It's "just a demo," according to director of marketing Doug Lombardi.
This video, from MaximumPCMag, is only a few seconds long but shows the player in control of P-body, meeting a damaged Atlas as part of a robot repair program educational trainer. The expanded machinery in the second part of the demo is actually Atlas' body arranged like an exploded diagram, with the player using Valve's new VR controllers to rotate and examine the parts.
[Valve has not announced Portal 3 with a VR demo - PC Gamer]