Why you might want to stay on Build 41
Build 42 became the stable branch of Project Zomboid on 29 July 2026. That is good news if you were waiting for it, but it is a problem if you are halfway through a long multiplayer save, because Build 41 worlds cannot be loaded by a Build 42 server. There is no converter and no migration path. The world either runs on Build 41 or it does not run at all.
The other common reason to hold is mods. Build 42 rewrote the modding framework, so a Build 41 mod list does not carry over. If your server's identity is a specific mod set, staying on Build 41 until those mods are ported is the sensible call.
Build 41 is not going away. The Indie Stone kept it on Steam as a permanent branch called legacy41, for both the game client and the dedicated server. This guide covers pinning your server to it so that nothing pulls Build 42 by accident.
First, check whether you are actually at risk
Open your server in the DoomHosting game panel and go to the Startup tab. Look at the Steam Auto Update variable.
- Steam Auto Update is
0(this is our default): the server only downloads game files when you reinstall. Your Build 41 world is not in danger from a simple restart. Pinning the branch is still worth doing, because it protects you against a future reinstall. - Steam Auto Update is
1: the container runs SteamCMD on every boot. The next time your server restarts, it will download Build 42 and your Build 41 world will no longer load. Pin the branch before you restart the server.
If you are not sure which world you are on, the fastest check is the version line at the top of your server console on boot.
Pin your server to the legacy41 branch
This takes about a minute and does not wipe anything on its own.
- Open your server in the DoomHosting game panel.
- Go to the Startup tab.
- Find the Steam Beta Branch [requires reinstall] variable.
- Set its value to exactly:
legacy41 - Save the startup settings.
That is the pin. From now on, any reinstall or auto-update pulls Build 41 rather than Build 42.
Note the value carefully. The old branch names you may have seen in older guides, unstable and b41multiplayer, no longer exist on Steam. Typing one of those gives you a branch SteamCMD cannot resolve, and the install fails.
Important: setting the variable does not by itself change the files already on your server. If your server is currently running Build 41 files, that is exactly what you want. Do not reinstall, because a reinstall wipes your world.
Back up the world anyway
Pinning the branch protects you from Steam. It does not protect you from a mistake, and the mistake in question deletes a save that cannot be regenerated.
Take a copy of the world before you do anything else. Our backup and restore guide walks through downloading the save folder from the panel. Keep that copy somewhere off the server. A Build 41 save is only useful on a Build 41 server, so if you ever lose it there is no way back into that world.
Tell your players to pin Steam too
The server is only half of it. Steam now hands Build 42 to every player by default, and a Build 42 client cannot connect to a Build 41 server. Unless your players opt in to the legacy branch, they will get a version mismatch when they try to join.
Send them these steps:
- Right-click Project Zomboid in the Steam library.
- Select Properties.
- Open Game Version & Betas.
- Select legacy41 from the dropdown.
- Let Steam download the older build, then launch the game.
This is per-player, and it is the single most common reason someone reports that "the server is down" when it is running perfectly well.
Mods on a Build 41 server
If you stay on Build 41, keep your existing mod list exactly as it is. Do not update mods to their Build 42 versions, because Workshop items that have been ported forward will stop working on your Build 41 server.
This is the reverse of the trap that catches people moving to Build 42, and it has the same root cause: Workshop IDs are not version-aware. Steam serves whatever the mod author published most recently, regardless of which build your server runs. When a mod author ports to Build 42 and drops Build 41 support, that mod will break on your server the next time it updates.
If a mod suddenly errors on a server that you have not touched, that is almost always what happened. Check the mod's Workshop page for a Build 41 legacy version, which many authors publish as a separate item.
Moving to Build 42 later
Nothing here is permanent. When your group is ready, or when the mods you care about have been ported, clear the Steam Beta Branch variable to go back to the public branch and reinstall with a file wipe.
The full procedure, including what to do about mods and what the first Build 42 boot looks like, is in How to Switch to Project Zomboid Build 42 Server.
Plan for Build 42 needing more memory than Build 41 at the same player count. Our RAM requirements guide has the numbers for both builds, and you can add RAM to your server in the panel without rebuilding it.
Troubleshooting
The server will not install after I set the branch. Check the value is exactly legacy41, all lowercase, with no spaces. legacy 41, Legacy41 and the retired b41multiplayer all fail.
My world is gone after switching to legacy41. A reinstall with the wipe option deletes server files including saves. Restore from the backup you took. If you did not take one, the world cannot be recovered.
One player gets a version mismatch, everyone else is fine. That player is still on the default Steam branch. Have them select legacy41 under Game Version & Betas.
Everyone gets a version mismatch after a restart. Your server had Steam Auto Update set to 1 and pulled Build 42 on boot. Set the branch to legacy41, reinstall, and restore your Build 41 save from backup.
A mod broke on its own. The mod author ported it to Build 42. Look for a Build 41 legacy version of the item on the Workshop and swap the ID in your mod list.
Frequently asked questions
Is Build 41 still supported? Steam keeps legacy41 as a permanent branch, so you can install and play it indefinitely. It is not receiving new features, and a security patch shipped alongside the Build 42 release, but it works.
Can Build 41 and Build 42 players share a server? No. The client and server builds must match.
Will DoomHosting force my server to Build 42? No. Your server runs the files on its own disk, and we do not reinstall customer servers. The change happens when you choose it.
Can I run one server on each build? Yes. They are separate servers with separate save data, and you can order a second Project Zomboid server and pin it to whichever branch you want.
Do I need to reinstall right now to pin the branch? No, and you should not. Setting the variable is enough to control what a future install pulls. Reinstalling wipes your world.
You can manage branches, backups and mods yourself from the game control panel, and our support team is available 24/7 if a branch switch does not go the way you expected.