How to Pin a Project Zomboid Build 42 Server to Version 42.13.1

Project Zomboid Build 42 multiplayer was released to Steam's Unstable branch with build 42.13 in December 2025 as a work-in-progress stress test. Because Build 42 updates can invalidate saves, The Indie Stone advised players to make backups.

Select a specific server version

The Project Zomboid dedicated server uses Steam app ID 380870. The documented SteamCMD command for installing the Unstable branch is:

app_update 380870 -beta unstable validate

Project Zomboid support moderators also documented 42.13.1 as a separate beta branch. To select that version instead of unstable, use:

app_update 380870 -beta 42.13.1 validate

This command specifically selects the documented 42.13.1 branch. It does not establish that every historical release remains available as a beta branch.

Keep clients on the matching branch

Players may be unable to connect correctly if their client and the server use different beta branches. In Steam, players can choose a branch under Project Zomboid → Properties → Betas. Tell players which branch the server uses before they connect.

Back up the world before updating

Back up the server save before applying an update. Saves created before 42.13 are not compatible with 42.13, so an older world should not be treated as safe to carry forward without a backup.

Dedicated-server data is stored in the Zomboid user directory. The cited server guide identifies these locations:

• Server configuration: Zomboid/Server/
• Multiplayer saves: Zomboid/Saves/Multiplayer/

Check mods and resources

For the Build 42 multiplayer test, The Indie Stone advised removing mods, including client-side mods. A dedicated-server guide also reports that Build 42 requires more RAM and CPU than Build 41, so check available resources when preparing the server.

Checklist

1. Back up the multiplayer save.
2. Run app_update 380870 -beta 42.13.1 validate to select the documented version branch.
3. Have players select the matching Steam beta branch.
4. Follow The Indie Stone's test guidance by removing mods, including client-side mods.
5. Confirm that the server has adequate RAM and CPU for Build 42.