They're not quite ready to put out SteamOS 3 Linux just yet (which is what the Steam Deck uses), or even an official developer image to install but "soon" something should be available in that way. Until then, they've come up with a way for developers to test everything on Linux a little easier.
It starts by going over the already expected essential things like gamepad input and resolution support but this time there's more detail on actually testing it on a Linux system. Specifically, Valve are now suggesting developers go for Manjaro KDE, as it's also based on Arch Linux and has the same Plasma desktop as you will find in the desktop mode with SteamOS 3 on the Steam Deck.
On top of that, Valve has created two new tools to help developers test their builds (either a native Linux build or a Windows build with Steam Play Proton) with the SteamOS Devkit Client Tool and the SteamOS Devkit Service. These tools allow developers to deploy game builds from a development machine to either a Steam Deck or another Linux machine for full testing. Valve also said to ensure developers use Proton Experimental when testing Windows builds.
Valve even gave a hint for developers wishing to buy a mini-PC with somewhat similar specifications to the Steam Deck, with their pictured suggestion being the MINISFORUM UM700 Ryzen NUC available on Amazon (US / UK) along with a picture using the banana scale:
- AMD Ryzen 7 3750H
- Radeon RX Vega 10 Graphics
- 16GB of DDR4 RAM
While it has a stronger CPU, weaker GPU and less memory bandwidth they say "it will definitely run well on Steam Deck" if it runs well on something similar to that.
Nice to see some more clear documentation go up, although it's a little crazy to think this has only just gone live considering the Steam Deck was supposed to launch next month.