It turns out a recent hire (or contractor) for Valve is Alyssa Rosenzweig, the developer who has done tremendous work on the Panfrost open-source, reverse-engineered Arm Mali graphics driver over the years. From there she went on to work at Collabora the past four years on Linux graphics. Since 2021 she's also been doing reverse-engineering on the graphics found with Apple M1/M2 SoCs and working with the Asahi Linux team on the AGX Gallium3D code for OpenGL with Apple Silicon on Linux.