Quote On Linux, the game will launch with OpenGL by default. However, an option to play using the Vulkan graphics API will be available via the Feral pre-game options window.

Article taken from GamingOnLinux.com.

Feral Interactive have just announced some exciting news! The Linux port of Dawn of War III [ Steam Feral Site ] will come with OpenGL as the default, but like with Mad Max you will be able to check a box to enable Vulkan!Okay, now I'm even more excited. Having trouble keeping my excitement under wraps here, feel like there's a small explosion inside trying to get out in response to this news.I will do my best to get some benchmarks done for release like I did with Mad Max, if it has a benchmark mode of course.Dawn of War III arrives on Linux on, so not long to go!Also, as a small extra announcement, I will be doing regular online games in Dawn of War III with the community. Exact dates and times to be determined, but let me know in the comments if you're up for joining in. Likely evening time, sometime around 20:30 UTC on a specific day.It's also highly probable I will be doing weekly games livestreamed on Twitch against someone from Feral once again.It's also certain I will do a release-day livestream on June 8th to celebrate! Keep an eye on our Twitch channel and the livestream schedule for more.Check out the trailer: