Windows and Linux users will be able to download the first three levels of the graphically updated game as shareware starting at 6am Pacific Time on June 6. You can play the remaining levels and multiplayer if you point the installer to a legit copy of the full game on your hard drive. The source code for the Vulkan-based update will be posted on Github as well, though Quake II expansion packs will not be supported without extra effort from the community.

source: ars