Your Steam client can now help load certain games a little more smoothly. The new shader pre-caching feature, which went into beta in November and now comes to all users via the latest stable client update, allows Steam to download pre-compiled shader code for OpenGL and Vulkan games. So instead of having your PC compile high level shader code into a version tuned for your GPU, Steam will snag it for you before you ever launch the game.
Note that the feature uses a "small amount" of bandwidth, and can be turned off in the settings menu if you're not cool with Steam messing with your shaders. The size of the shaders should be fairly negligible compared to the gigs and gigs games themselves require these days, though, and you can see how much space they're taking up in the settings. With Wolfenstein 2: The New Colossus and a variety of other games installed, one of our Steam clients was holding onto just 9 MB of shader data.
Pre-compiled shader caching is not new in general—AMD and Nvidia both cache compiled shaders after a game's first load—but Valve clearly felt there was more to be done for OpenGL and Vulkan-based games.
The update also includes a host of controller support improvements, including treating the controller like a mouse if a game opens a launcher before actually launching. "Several dozen Xbox-compatible controllers" will now be properly detected as Xbox controllers, rather than generic controllers, and Steam now supports a few more PS4 controllers: the HORI TAC4, HORI TAC PRO, Hitbox PS4 Arcade Stick, and Venom PS4 Arcade Stick.
There's a lot more, including bug fixes and an update to the web browser. You can read the full patch notes on Steam.