The Indie Stone released Project Zomboid Build 42.21 to the stable branch on September 28, 2026, five days after it went into public testing, according to the studio’s Steam announcement. It is the first incremental update since Build 42 itself reached stable this summer, and the studio says testers reported no major issues, so the build shipped as tested.
What Build 42.21 Changes
The Indie Stone singled out three headline changes:
- Zombies stop vanishing. A bug that made zombies disappear after a player left and re-entered a chunk of the world is fixed in single-player and multiplayer, along with the worst zombie duplication in multiplayer. It hit high-population games hardest. The studio says some instances remain and are due to be fixed in the next update.
- XXL trees get out of the way. They cut away better when you are in a vehicle, no longer hide the houses and furniture they overhang, and are more transparent overall. The studio calls this a work in progress.
- loadstring and loadstream are back. The 42.20.4 hotfix disabled both Lua methods over security vulnerabilities; after further investigation, The Indie Stone has re-enabled them.
The 42.21 testing notes list the rest. Welders now start with Welding recipes instead of Blacksmithing, 86 more fluid containers can purify water in the right oven, washing machines clean dirty rags and bandages, fridges and freezers warm gradually on the day the power goes out, and explosives now work in basements. Split-screen play stops sharing read-book status and XP boosts incorrectly, and multiplayer gets expanded anti-cheat, a fix for an exploit that let players join dedicated servers without Steam authentication, which kept SteamID bans from working, and smoother high-ping driving.
The Indie Stone also says this should now be the standard routine for every release: Unstable first for player testing, then Stable. During testing the studio said 42.20.4 saves should not be affected, though it recommended backing up a save before trying the new build.
What This Means for Players
If you run large zombie populations, this update is aimed squarely at you: hordes should now stay put when you walk away and come back. Modders and server admins get the bigger relief. Mods that broke after 42.20.4 because they relied on loadstring may work again, so check each mod’s Workshop page before assuming it is dead. Our 50 best Project Zomboid mods list labels every pick by the build it supports.
If you want more survival with friends, our best PC co-op games of 2026 list includes Grounded 2, and our best horror games of 2026 list covers the scarier end of the genre.
Source: The Indie Stone, “Build 42.21 Stable Released,” Steam, September 28, 2026.