How to keep a Build 41 world and a Build 42 world on one server

A Project Zomboid world made on Build 41 does not load on Build 42, and the other way round. To keep both on one server, put each in its own Instance: an instance has its own files and its own settings, and you switch between them with one click. Only one instance runs at a time.

We have not tested this exact route on a Project Zomboid server ourselves. It uses the standard Instances feature of the panel, which keeps each instance's files apart. Take a backup before you start.

Set it up

1. Make a backup of the world you have: How to back up and restore your Project Zomboid world.
2. Open Instances in the left menu and click Create new. Choose the server software and give it a name you will recognise, for example Build 41. See How to use instances to switch between worlds on one server. You need a free instance slot, which comes from your plan.
3. Click Switch & play on the new instance and confirm Switch. The server stops, moves its files and builds the new instance.
4. In the new instance, open Settings, then Game Settings, and set Beta Branch to Build 41 legacy. The panel asks Switch between Build 41 and Build 42? Confirm with Switch build: there is no old world in this instance to lose.
5. Start the server. The build installs at the start, which takes a few minutes. With Steam Auto Update off, use Update now on the Game Settings page: How to update your Project Zomboid server.

Switch back

Open Instances and click Switch & play on the other instance. Players must change their Steam branch to match: the game's Properties, then Betas. See How to choose Build 41 or Build 42 for your Project Zomboid server.

Good to know

• Mods are different for each build. Add the right ones in each instance: Project Zomboid mods and Build 42: what to know.
• The Sandbox Settings editor only opens Build 42 files. A Build 41 instance shows a message that the file is from a different build, and you edit it under Files: Project Zomboid Sandbox Settings says the file is from a different build.
• If you only want to move one world to Build 42, there is no conversion: a Build 41 world does not load there.