Want to get more info behind the scenes on how Steam for Chrome OS works? It uses Linux but it's a little bit complicated and Google has put out the first in a series of blog posts to talk more about it.
The good news of course for normal Linux desktop fans, is that developers will need to ensure their games work on Linux directly. Either through a Native build, which should work out of the box, or ensuring and testing their Windows builds with Proton. Although, Steam Play Proton is not turned on by default for Chrome OS as there's various issues right now.
How does it work then? Through the magic of virtual machines! Using work they've done in the past with Crostini, an already existing way to run normal Linux apps on Chrome OS and "Chrome OS's own virtual machine monitor (VMM), crosvm". They say running Steam and games in a container like this "provides another layer of security above normal Linux systems" that's used for Crostini, Android, and Parallels.
Their system, much like SteamOS for the Steam Deck, is based on Arch Linux which they codenamed "Borealis", and it's automatically kept up to date for you with each Chrome OS release. Keeping it simple, while hiding all the technical parts for users, as they say "we have aimed to make the VM invisible to the user – from both an operational and from a performance perspective". They do this by using "Linux's KVM hypervisor" and "paravirtualized virtio-based devices instead of emulation" and that to play the latest games they built a Vulkan virtualization driver called "Venus".
Borealis and Crostini differ in a number of ways, while still sharing the core graphics and display pipeline, so applications support Vulkan and OpenGL using Mesa drivers. It uses XWayland, together with "sommelier", which they say is their "proxying Wayland compositor" and then it all moves over to "exo" which is their own Wayland display server. The big difference is user experience with Borealis targeting end users and Crostini for developers, with Borealis enabling one-click installs like Steam. The other big difference is that Borealis is based on Arch Linux, while Crostini is based on Debian.
The way they've configured it sounds a lot like the Steam Deck too, with the VM being read-only while having a separate read-write partition for data and they're shipping newer versions of Mesa than what is usually tagged as a release upstream.
Google said to expect "deep dives" on their Steam integration, their Vulkan virtualization, how to develop games for ChromeOS and much more. We can also expect "new devices, new features, better integration and improved performance".