Steam games: updates, versions, branches
How a Steam game server updates, why players can't join after a patch and how to choose a beta branch.
Updates
The server updates the game on every start if Auto Update = 1 is enabled in "Startup". After a patch is released, simply restart the server.
If players report "incompatible version" after a patch, the server is still on the old version. Restart it (and check that Auto Update = 1).
Beta branches and old versions
Some games (Project Zomboid, Valheim, Rust) let you choose a Steam branch. "Startup" has a Beta ID / Branch parameter. Important: every player must be on the same branch (Steam → the game → Properties → Betas), otherwise they won't get in.
A specific old build that isn't among the Steam branches can't be installed: Steam no longer distributes it.
The first install takes a while
The first start downloads the whole game, from 2 to 15 GB. That takes 5–20 minutes. If the console shows "Missing configuration" or "state is 0x…", start it again and Steam will resume the download.