How to Install Project Zomboid Build 42 (B42) on Your Server

About Build 42 (B42)

Project Zomboid Build 42 (B42) is the latest major update from The Indie Stone, released as an opt-in unstable branch on Steam. B42 brings a new map, new crafting and animal systems, and a graphics overhaul. Because it is still in beta, you must switch your server to the unstable branch on Steam to install it.

This guide walks you through switching your Pterodactyl-managed Project Zomboid server from the default (B41) branch to the B42 unstable branch.

Before You Start

• B42 saves are not compatible with B41. Once you load a world on B42, you cannot open it on B41 again without restoring a backup
• Most B41 mods will not work on B42 — see How to Add Mods to Your Project Zomboid Server for B42 mod compatibility notes
• B42 uses more RAM than B41. If your server has 8 GB or less, review Project Zomboid B42 — Server Fails to Start (Out of Memory) before starting the server for the first time

Step 1: Back Up Your Server

The reinstall in Step 4 will overwrite your installation. Back up first so you can roll back to B41 if needed.

1. Go to the Backups tab in your game panel and click Create Backup
2. Wait for the backup to finish before continuing
3. For a full walkthrough, see How to Create and Restore Server Backups

Step 2: Switch to the Unstable (B42) Branch

1. Open your server in the Game Panel
2. Go to the Startup tab
3. Find the Branch / Version variable (the one that controls which Steam build is installed)
4. Change its value to unstable
5. Save the change

Need to confirm the branch name? Check the public depot list on SteamDB: steamdb.info/app/380870/depots/. The branch column shows every public branch — unstable is the current B42 branch as of this writing.

Step 3: Delete Existing Server Files

1. Go to the Files tab
2. Select all files and folders in the server root
3. Click Delete and confirm

Why delete everything? The reinstall in Step 4 only re-runs the SteamCMD installer — it does not wipe existing files. If the old B41 binaries are still on disk, SteamCMD will skip files it thinks are already installed, leaving your server in a broken half-B41 / half-B42 state that fails to start. Wiping the directory first guarantees a clean B42 install.

Your worlds and save data are safe as long as you completed the backup in Step 1.

Step 4: Reinstall the Server

1. Go to the Settings tab
2. Scroll to the Reinstall Server section
3. Click Reinstall Server and confirm
4. Wait for the install to complete — the panel will show the SteamCMD download progress in the console. This can take several minutes

Step 5: Start and Verify

1. Click Start on your server
2. Watch the Console tab — on first boot, B42 will generate fresh server config files
3. Confirm the version line in the console reads Build 42 (or similar B42 version string) and not 41.x
4. Connect from your Project Zomboid client (make sure your game client is also on the unstable branch — B41 clients cannot join B42 servers)

Reverting Back to B41

If B42 does not work out, you can roll back:

1. Stop the server
2. Go to the Startup tab and change the Branch / Version variable back to public (the default B41 branch)
3. Delete all files in the Files tab (same reason as Step 3)
4. Reinstall the server from the Settings tab
5. Restore your B41 backup from the Backups tab

Important: Do not try to load a B42 save on B41 — it will not work. Always restore the matching B41 backup after rolling back.

Common Issues

• Server fails to start with a Java memory error — see Project Zomboid B42 — Server Fails to Start (Out of Memory)
• Server still shows Build 41 in the console — the old files were not fully deleted. Stop the server, repeat Step 3, then reinstall again
• Players cannot connect — their game client is likely still on B41. They need to opt into the unstable branch in Steam (right-click Project Zomboid → Properties → Betas)
• Mods crash the server — most B41 mods are incompatible with B42. Remove all mods first, confirm a clean B42 server starts, then re-add only B42-compatible mods one at a time