This is quite exciting for the future of Virtual Reality, as Valve as now properly given their backing to the OpenXR standard and added support into SteamVR.
What is OpenXR? Overseen by The Khronos Group, who also oversee the OpenGL / Vulkan APIs, it's a royalty-free, open standard that provides high-performance access to Augmented Reality (AR) and Virtual Reality (VR). This way, developers can begin to target OpenXR and have it run cross-platform for XR (AR/VR). Standards like it are important so developers don't have to rewrite code to target each company going their own way with XR.
Thanks to The Khronos Group and the extensive hard work of OpenXR's many members (AMD, ARM, Epic, Facebook, Google, HTC, Microsoft, NVIDIA, Qualcomm, Unity, Valve, and many more) VR now has a consolidated API to enable developers to bring universal VR support to their applications.Valve
With OpenXR, for the first time, developers will be able to build their content in a way that will allow them to span the myriad types of hardware and software platforms.
Valve said this is only the start and they will continue expanding their support of OpenXR, with the developer preview currently supporting OpenXR 1.0.9. Sounds like support for OpenXR is quite far along too, with it passing "95% of conformance tests".
It's not enabled for all users, as it's under a Beta channel you need to opt into and it's currently aimed at developers to test with. It supports working with Vulkan on both Linux and Windows.
You can see their announcement here.