Valve's SteamOS Now Supports Vulkan, The Cross-Platform Alternative To DirectX 12 (pcworld.com)
SteamOS just gained support for Vulkan, the cross-platform alternative to Microsoft's DirectX 12 and Apple's Metal. This should make it easier for developers to write and optimize games for SteamOS, closing the performance gap with Windows and encouraging more developers to support Linux. This feature arrived in SteamOS Brewmaster version 2.63. Valve added version 355 of the Linux Nvidia driver, which means SteamOS offers Vulkan support when used alongside Nvidia hardware. Intel's graphics hardware should also support Vulkan on SteamOS in the near future. AMD is still working on its new driver, known as AMDGPU, that will replace the current fglrx driver for SteamOS and other Linux-based platforms. If you use Linux distribution besides SteamOS, you can download Nvidia's Vulkan-ready Linux driver or an experimental version of Intel's Vulkan-enabled graphics driver.
I was surprised to learn that very few games are running on DX12 (maybe 1-3?)..
Vulkan already has one and it's looking likely to get more. I'm guessing Valve at least will port all their modern titles to it. If so, Valve is really playing the long game on becoming less dependent on MS Windows..
Cross Platform? Please tell me that it means more than just Windows + Linux, and that I can install & run it on FreeBSD
The statement is "the cross-platform alternative to DirectX 12" - specifically 12, and not DirectX in general. On Windows your options for Mantle-like APIs are currently Vulkan and DirectX 12, i.e. the platform-limited alternative to Vulkan is DirectX 12, and the cross-platform alternative to DirectX 12 is Vulkan. I hope that helps you feel a bit better about the headline.