Valve just added a Vulkan beta upgrade to Dota 2, the firm's massively popular multiplayer on-line battle arena (MOBA) game, a.k.a. far and away the most-played game on Steam. The Vulkan graphics API is designed as an open competition to Microsoft's DirectX 12. Anyone interested in trying out Vulkan will find it in the game's DLC section on Steam, as first found by Tom's Hardware.
Getting Vulkan to power Dota 2 is not as easy as clicking a box. The graphics API has to be enabled with the -vulkan flag in the launch options, and you also need to remove DirectX and OpenGL flags if you see them. Valve also says you have to be running the Steam Client Beta. Valve has instructions on the best way to do that - to get the Vulkan version of the Steam Overlay.
Vulkan's still in beta mode with Dota 2 so there are a few known problems. Valve says you may see some short stuttering on startup related to a shader caching issue, and Linux players with Nvidia graphics cards may see some display tearing even if VSync is turned on.