Project Zomboid Build 42.21 has moved from the Unstable branch to Stable. The official Steam announcement (Steam) was published on September 28, 2026 at 12:07:08 UTC; that timestamp does not confirm a separate deployment time.
The update focuses on zombie-management problems in solo and multiplayer, with the clearest impact expected in sessions containing large zombie populations. It also adjusts XXL tree visibility and restores two Lua methods for modders and server administrators.
Zombie duplication and disappearance are the main targets
Build 42.21 addresses zombie duplication in multiplayer and cases where zombies disappeared after a player left and later re-entered a world “chunk.” The announcement says both issues could occur in solo and multiplayer games and were particularly noticeable when the zombie population was high.
The Stable release follows the update’s earlier arrival on the Unstable branch the previous Wednesday. According to the announcement, the community reported no major problems during that phase. Some occurrences of the zombie issues still remain, however, and are scheduled for correction in a future update.
XXL trees should obstruct the view less often
The update changes how XXL trees are hidden during play. They now fade more effectively for players in vehicles and no longer conceal the houses and furniture beneath them. Their overall transparency has also been adjusted.
These visibility changes are still considered a work in progress, so Build 42.21 is not the final word on how oversized trees behave.
Two Lua methods return after security work
Build 42.21 reactivates the Lua methods loadstring and loadstream. They had been disabled in version 42.20.4 while the developers worked on security vulnerabilities, then returned after a further investigation.
The change matters most to mod creators and server administrators, who regain access to methods previously removed as part of that security response. The announcement credits Scribl, also known as Boris, and Rasmus Moorats, also known as nnsee, with helping report the vulnerabilities addressed in 42.20.4.
A Stable release with more fixes ahead
For players, Build 42.21 improves several visible and practical problems without claiming that zombie behavior is fully resolved. Modders and server administrators also recover two Lua methods, but their return remains tied to the security investigation that originally led to their removal.
Build 42.21 brings these changes to Stable for solo and multiplayer sessions, especially those with dense zombie populations, while further corrections and tree-visibility work remain ahead.
More Project Zomboid coverage:the Project Zomboid page.
