Project Zomboid Build 41 vs Build 42 Multiplayer: Which to Run?

For most Project Zomboid multiplayer groups in 2026, Build 42 is the right choice: it has been the stable, default branch since 29 July 2026, gets every fix, and adds the new crafting, animals and basements. Pick Build 41 (legacy41) only to finish an old B41 world or keep mods that have no Build 42 version.

What is the difference between Build 41 and Build 42?

Build 42 is the biggest update in Project Zomboid's history. Build 41 is the version most players knew for years, and the one that introduced the multiplayer most servers ran on.

Sources: The Indie Stone's Build 42 stable plans, the 42.20.0 release and the 42.20.4 and 41.78.21 hotfix post.

Is Build 42 multiplayer stable now?

Yes, in the sense that matters: it is on the public stable branch and fully supported. Multiplayer first became playable on the Unstable branch in December 2025 and reached stable with 42.20 on 29 July 2026. The first weeks brought real issues, including "Loading Map" hangs and memory leaks, which hotfixes 42.20.1 to 42.20.3 addressed. 42.21 then fixed disappearing and duplicating zombies in multiplayer.

The Indie Stone still lists known issues, so Build 42 multiplayer is solid but not finished. See our 42.21 update breakdown for the latest fixes.

Can Build 41 and Build 42 players play together?

No. The client and server must be on the same build. A Build 41 game cannot join a Build 42 server, and the server browser only shows servers on your build. Since 42.21, players who try to join a server on a different version get a clear notification.

Can I move a Build 41 world to Build 42?

No. The Indie Stone states plainly that Build 41 savegames are not compatible with Build 42. Even 42.19 Unstable saves could not move to 42.20 because of new map content. A Build 42 server needs a fresh world.

That is the main reason to keep a B41 server: a long running world your group has not finished. When you are done with it, start fresh on Build 42.

Which build is better for modded servers?

Build 41 still has the bigger, more complete mod library, since it had years of development. Build 42 mods are catching up quickly, especially since stable launched, and The Indie Stone has promised more modding support, mapping tools and an animation editor.

Check each mod's Workshop page for the build it supports. Some practical differences on a B42 server:

• Mod IDs in the server config need a backslash in front, for example \ModName.
• Many B41 mods load on B42 and then break in odd ways. If a mod only lists B41, assume it does not work.
• Security hotfixes changed Lua rules in 2026: 42.20.4 removed loadstring and 42.21 restored it, and 42.20.2 changed % handling in mod text.

Our guide to adding mods to a Project Zomboid server covers both builds.

How much RAM does each build need?

Build 42 is hungrier than Build 41 for both RAM and CPU. As a rough guide for a dedicated server:

Our how many players guide goes deeper into sizing by group.

How do you switch a server between Build 41 and Build 42?

On a self hosted server, install with the branch you want:

steamcmd +login anonymous +app_update 380870 -beta legacy41 validate +quit

Leave out -beta legacy41 for Build 42. Use a separate install folder or back up Zomboid/Saves and Zomboid/Server first, because the builds do not share worlds.

Every player then picks the same branch in Steam:

1. Right click Project Zomboid and click Properties.
2. Open Game Versions & Betas.
3. Pick legacy41 for Build 41, or the default for Build 42.

Which should your group pick?

• New group, new world: Build 42.
• Finishing a B41 world: stay on B41 until you are done, then start a B42 world.
• Depends on a mod with no B42 version: B41 for now, and check back after each B42 update.
• Large public server: Build 42, for the active anti-cheat and fixes, and budget more RAM.

Running either build on GamezServers

Our Project Zomboid servers have two server types: Build 42, the default, and Build 41 (legacy) on the legacy41 branch. You can keep a B41 world on one server and start a B42 world on another, and switching type keeps your files on disk. Every start updates the server, and the Java heap is sized to your plan. Plans are 6, 8 and 12 GB on Project Zomboid server hosting.

FAQ

Is Project Zomboid Build 42 out of beta?

Yes. Build 42 became the stable, default branch with version 42.20 on 29 July 2026.

Can I still play Build 41 multiplayer?

Yes. Select the legacy41 branch in Steam, and run the server on the same branch. It received a security hotfix, 41.78.21, on 26 August 2026.

Do Build 41 mods work on Build 42?

Not reliably. Use mods that list Build 42 support on their Workshop page, and remember the backslash in front of each Mod ID.

Will my Build 41 save work on Build 42?

No. Build 41 saves are not compatible with Build 42, so you need a new world.

Does Build 42 need a better server?

Yes. Plan for roughly 2 GB more RAM than the same group needed on Build 41, and a fast CPU.