Build 42 vs Build 41 on a Project Zomboid Server: What Changes
Since 29 July 2026, Build 42 has been the normal version of Project Zomboid on Steam, multiplayer included (it's on 42.21 now). For a server, four things change: Build 41 saves don't load in 42, lots of mods have to be swapped, it needs more RAM, and everyone has to be on the same version. If your group would rather stay on 41, you can.
When multiplayer came to Build 42
Build 42 first came out without multiplayer, on Steam's unstable branch. Multiplayer reached that branch at the end of 2025, with 42.13, and the normal version on 29 July 2026, with 42.20. Since that day, anyone who buys or updates the game on Steam gets 42.
Since then there have been patches with lots of server work. 42.20.3 (August 2026) supports up to 254 players and lets admins in even when the server is full. 42.21 (28 September 2026) fixes zombies that duplicated or vanished when the map reloaded, improves driving with high ping, closes a hole that let people join without going through Steam (so SteamID bans really work), shows the date of the last world wipe in the server list (not the last restart), and tells players when their version doesn't match the server's.
Supporting 254 players doesn't mean it runs well with 254: the game itself warns in the .ini that with more than 32 at once there can be map loading problems and desync.
Rather not set it up yourself? Project Zomboid servers from €12 a month, no contract and a full refund within 72 hours. Or create a free Project Zomboid server, no card needed.
What changes for your server
Saves. A Build 41 world doesn't open in 42: they store data differently and there's no official converter. Saves from the earlier unstable 42 (up to 42.19) don't open in 42.20 either, because the map changed. You'll need to start a new world.
Mods. They have to be made for 42: many unported 41 mods don't even show up, and others load but fail silently. How they're written in the .ini changes too: on 42, each Mod ID on the Mods= line has a backslash in front (Mods=\ProximityInventory;\RainCleansBlood). Without it, they don't load. The Workshop mods guide explains it all.
RAM and CPU. Build 42 simulates more (animals, for example, live and move around even with nobody nearby) and needs more memory. We tested it on 4 GB and it runs with barely half a gig to spare, so the rule of thumb is 6 GB minimum and 8 GB with lots of mods. The Project Zomboid RAM guide explains it for your group.
The game itself. Animals and farming, basements, a new crafting system with professions, and a map with new content since 42.20. For players it's a different game (what Build 42 brings to group play); for admins, more to keep an eye on in the settings (the animal ones, among others, in the SandboxVars file: the sandbox settings).
Is it worth staying on Build 41?
Build 41 is still available and still gets security patches (the latest, 41.78.21, in August 2026), but no new content. Its advantage is that it has been stable for years and almost every Workshop mod works on it.
If you're starting from scratch, go with 42: it's where everything new lands, and more and more mods are moving to it. If you have a months-long 41 world with a long list of mods that don't exist for 42 yet, it makes sense to finish it on 41 and switch afterwards.
How to stay on Build 41 (legacy41)
Build 41 is on a Steam beta branch called legacy41. What can't happen is some of you on 41 and others on 42: the server only lets in players on its own version.
Every player, in their own Steam
Right-click Project Zomboid → Properties → “Betas” (in the new Steam, “Game Versions & Betas”) and choose legacy41. Steam downloads 41 and keeps it that way until you change it.
The server, on the same branch
Steam's dedicated server (Project Zomboid Dedicated Server) is switched the same way, from its properties. If you install it with SteamCMD, you choose the branch when downloading it.
Back up before switching
Switching branches doesn't delete saves, but a world opened on the wrong version can get corrupted. Copy the Zomboid folder in your user directory before touching anything.
Moving from 41 to 42 without losing anything
Keep the 41 world
Copy its folder (in Saves/Multiplayer) somewhere else. Even though it won't open in 42, you'll have it if you ever go back to 41.
Swap the mods
Check each mod on the Workshop: it should say it's for Build 42 and have been updated since July 2026. Look for alternatives to the ones that aren't; these work in multiplayer on 42.
Start a new world
With the server stopped, move the old world's folder aside and start it up: a new one is created. The guide to resetting a Project Zomboid world explains it step by step.
Go over the settings
Build 42's SandboxVars has settings 41 didn't (animals, among others). Look at them before anyone joins: some only count in a new world.
With NapNodes
Our servers install Steam's normal branch, currently Build 42 (42.21), and no Project Zomboid server goes below 6 GB because of what 42 needs. In the panel's “Mods” tab, any mod marked as Build 41 only shows a warning, and the panel adds the backslash that 42 needs.
If your group needs Build 41, write to us in “Help” before touching anything: switching branches means reinstalling the server's game, and a world from one branch doesn't open on the other.
Frequently asked questions
Does Project Zomboid Build 42 have multiplayer?
Yes. It reached the unstable branch at the end of 2025 and Steam's normal version on 29 July 2026, with 42.20.
Can I move my Build 41 save to Build 42?
No: Build 41 saves don't open in 42 and there's no official converter. Keep the folder in case you go back to 41 and start a new world.
How do I go back to Build 41 on Steam?
Right-click the game → Properties → “Betas” (or “Game Versions & Betas”) and choose legacy41. Everyone in the group and the server have to be on that same branch.
Do Build 41 mods work on Build 42?
Only if the author has ported them. Check on their Workshop page that they say Build 42 and have been updated since July 2026; in the Build 42 .ini, each Mod ID has a backslash in front.
What's the latest version of Project Zomboid?
On Steam's normal branch, 42.21, since 28 September 2026. Your version is shown at the bottom of the game's main menu; if it doesn't match the server's, here's how to update.
Shall we set it up for you?
Project Zomboid servers from €12 a month, never oversold: your RAM is yours alone. And if you'd rather start without paying, there's a free Project Zomboid server, no card needed.
Not sure whether your server is online? Check it in a second with the Project Zomboid server status checker: players, version and password, free.
Free tool: Project Zomboid settings editor. Paste your .ini and SandboxVars.lua (or start from scratch), change their 400+ options with a search box, and download them.