With the recent release of DXVK 2.0, the Direct3D 9 / 10 / 11 to Vulkan translation layer, it pulled in DXVK-Native for Native Linux builds and so Valve has upgraded Half-Life 2, Portal, Portal 2, Left 4 Dead 2.
So what does this mean? Well, the original Linux ports used TOGL to convert the original Windows Direct3D rendering system over to OpenGL. Then Valve began updating each of them all to DXVK last year to give them better performance on Linux desktop and Steam Deck. With DXVK 2.0, they're ready to take advantage of all the extra performance improvements to be found there.
Why the need for the translation between graphics APIs? This was before Source 2, which eventually gained Native Vulkan support, so these older ports didn't have it available. Portal 2 additionally noted in the update it had "Fixed some controller input bugs" as well. Nice.
Great to see Valve support their classic titles for so long.
Hopefully we will find out whatever NEON PRIME actually is from Valve soon.