How to stay on Project Zomboid Build 41 (legacy41)

Build 42 is now the default stable Project Zomboid release. If you want to keep playing Build 41 (for example for an existing world or B41-only mods), opt into the Steam branch legacy41 (Build 41.78.20) on both your AleForge server and every player’s game client.

Caution

Server and clients must match. A Build 42 client cannot join a Build 41 server (and vice versa). Build 41 and Build 42 saves are not compatible — always create a backup before changing branches.

Tip

Accidentally updated to Build 42? If you restarted or reinstalled without legacy41 set and the server pulled Build 42, restore a Build 41 backup from the Backups tab in the AleForge Panel, then set Steam Beta Branch to legacy41, reinstall, and start again. Keep automated backups enabled so you always have a restore point — see How do I Setup an Automated Backup of My Server?.

Set the AleForge server to legacy41

1. Open the AleForge Panel
2. Stop the server
3. Create a backup from Backups
4. Go to Startup
5. Set Steam Beta Branch to legacy41
6. Go to Settings → Reinstall Server and confirm
7. Start the server once installation finishes

Changing the beta branch only takes effect after a reinstall. Leave Steam Beta Branch blank if you want the default stable Build 42 instead.

Set the Steam game client to legacy41

Every player who joins must also use Build 41:

1. In Steam, right-click Project Zomboid → Properties
2. Open Game Versions & Betas (or Betas on older Steam UI)
3. Under Selected Game Version, choose legacy41 (Build 41.78.20)
4. Close the window and wait for Steam to download the Build 41 files

Default Public Version is Build 42 (stable). Use that only when your server is also on Build 42.

Return to Build 42 (stable)

1. On the server: clear Steam Beta Branch (leave blank) → Settings → Reinstall Server
2. On each client: set Steam back to Default Public Version
3. Start the server after the reinstall finishes

Do not reuse a Build 41 world on Build 42 without expecting breakage. Start a new world or restore from a Build 42 backup.

Related

• Project Zomboid Build 41 vs Build 42: which should I run?
• How do I Setup an Automated Backup of My Server?
• How do I update my Project Zomboid server to Build 42?
• How do I configure my Project Zomboid server?
• How to Add Mods to a Project Zomboid Server