It’s no secret that Microsoft’s Mixed Reality platform will support SteamVR games over time. That’s a big deal because Steam is, after all, the largest store for buying PC games and Microsoft needs a large catalog of VR games to jumpstart its ecosystem. Until now, though, we didn’t really know what the timeline for this would look like.

As the company announced today at a small press event in San Francisco, developers now have access to the Windows Mixed Reality SteamVR preview to help them test their games. This holiday season, consumers will also gain access to this preview program.

It’s worth noting that Microsoft does call all of this a preview program, but there can be no doubt that SteamVR support is going to be very important to this platform. VR is already going through a bit of a tough phase and sales of existing headsets has slowed quite a bit. The last thing Microsoft wants is to have a lot of headsets on the market for the holidays but no content for its users. Both the Oculus Rift and HTC Vive headsets currently support SteamVR games.

Even with SteamVR support, it remains to be seen what the killer app for Windows Mixed Reality will be. The top-selling VR game on Steam right now is Job Simulator, followed by zombie apocalypse survival game Arizona Sunshine.

Microsoft also today demoed one if its first VR games, which unsurprisingly features its Halo franchise. Together with 343 Industries, Microsoft built a demo experience that brings the Halo characters to mixed reality for the first time.