Project Zomboid: Playing Build 42, and What the Unstable Branch Is For
Build 42.20 went stable on 29 July 2026. B42 is no longer a beta branch you opt into, it is the supported build, and Project Zomboid passed its all-time peak player count the day it landed. If anything below describes B42 as unstable or upcoming, read it as history: the branch it refers to is now the default. The one live caveat is mods, since a lot of Workshop items have not been republished for stable yet, so a list that worked last week can fail today.
Build 42 is the massive Next-Gen update for Zomboid, featuring animals, crafting overhaul, and basement/skyscraper tech. Since 42.20 on 29 July 2026 it is the default public build, so you no longer opt into a beta to play it. The Unstable beta still exists and runs ahead of public, currently 42.21, and that is what the warnings below are about.
1. Expect Bugs on Unstable
"Unstable" means exactly that. On that beta a server may crash, a save may corrupt, and mods break as the build moves. The public build does not change under you the same way.
2. No Going Back
Once a world is loaded in B42, it cannot be downgraded to B41. Always make a backup.
3. Mod Compatibility
A B41 mod needs a B42 update to work, and plenty of Workshop items still have not had one. Check each mod says it supports B42 before adding it to a server list.
How to Switch Server Version
Option 1: The Switcher (Supercraft Panel)
Nothing to switch: the Stable option installs Build 42, so a new server is already on it. To move an older server up to the current build:
- Go to Update / Switch Version.
- Pick the version you want, or leave it on the latest.
- Check "Wipe World" only if you are jumping from Build 41, because B41 saves do not load in B42.
- Click Update & Restart.
Option 2: SteamCMD (Manual)
If self-hosting, the public build is Build 42 and needs no beta flag:
app_update 380870 validateAdd -beta unstable only if you specifically want the build that runs ahead of public.
Client Instructions
You cannot join a B42 server with a B41 client. A client that is not opted into any beta is already on Build 42, so most players need to do nothing. If yours is still on the Build 41 legacy beta:
- Right-Click Project Zomboid in Steam -> Properties.
- Go to Betas.
- Select "None" to return to the public Build 42 build, or "unstable" only to follow the build ahead of public.
- Wait for download (~3-4 GB).
Notable B42 Features to Test
- Animals: Look for deer and cows in rural areas.
- Basements: Try digging a cellar (requires new tools).
- Lighting: The new propagation engine makes nights much darker and flashlights more realistic.
Host your Project Zomboid server with Supercraft and Build 42 is installed for you, with the version picker to move it up as new builds land.