Project Zomboid 42.21 is now Stable with major multiplayer and server fixes

Project Zomboid Build 42.21 has officially moved to the Stable branch, bringing an important batch of multiplayer fixes for dedicated servers. Zombie duplication, disappearing populations, network synchronization and Steam authentication are all addressed, while two Lua functions important to modders and server administrators have also returned.

After first deploying 42.21 on the Unstable branch, The Indie Stone has now considered the update ready for wider adoption. For multiplayer communities that deliberately wait for Stable releases before updating persistent worlds, this is the milestone that matters.

Project Zomboid 42.21 fixes zombie duplication on multiplayer servers

One of the most important fixes concerns zombie population management in multiplayer.

Build 42.21 corrects major cases where zombies could be duplicated on multiplayer servers. It also addresses situations where zombies could disappear when a player left an area and the corresponding chunk was later loaded again.

The problem could become particularly noticeable on servers configured with large zombie populations, making the fix especially relevant for hardcore communities and long-running persistent worlds.

A more reliable Build 42 experience for persistent multiplayer worlds

The zombie fixes are particularly important because Project Zomboid does not simply treat enemies as disposable entities around the player. On a persistent server, population management is part of the simulation itself.

Unexpected duplication can progressively distort the intended zombie population of an area, while disappearing zombies can have the opposite effect. Both behaviours can therefore affect the balance of a multiplayer world over time.

Moving these fixes to Stable makes Build 42.21 considerably more attractive for server administrators who avoided deploying an Unstable build on an established community server.

Multiplayer synchronization also receives several fixes

Build 42.21 also continues The Indie Stone's work on multiplayer synchronization.

Several networking-related problems have been addressed during the 42.21 development cycle, including situations where higher latency could cause terrain loading issues while driving, passenger teleportation or visible juddering between players.

A desynchronization problem involving player Z-level coordinates has also been corrected.

These improvements are especially useful for public and community servers, where players may connect from very different locations and therefore experience different latency conditions.

Steam authentication and anti-cheat protections are improved

Server security is another part of the update.

The developers have expanded Project Zomboid's multiplayer anti-cheat systems and corrected several exploits, including problems affecting safehouses.

More importantly for public dedicated servers, the update fixes a situation that could allow players to connect without being correctly authenticated through Steam.

This could interfere with SteamID-based bans and make server moderation less reliable. Build 42.21 corrects the authentication behaviour, strengthening the tools available to administrators running public communities.

Lua loadstring and loadstream return for mods and server tools

Build 42.21 also brings an important change for modders and administrators of heavily customized servers.

The Lua methods loadstring and loadstream have been re-enabled.

Both functions had previously been disabled while The Indie Stone investigated potential security issues. Following that investigation, the studio decided they could return in 42.21.

The developers also acknowledged that their temporary removal had caused disruption for mod creators and server administrators relying on them.

Why the Stable release matters more than the previous Unstable build

Most of these changes were already visible while 42.21 was being tested on Project Zomboid's Unstable branch. For a dedicated server, however, an experimental release and a Stable release do not carry the same implications.

Persistent multiplayer worlds can contain hundreds or thousands of hours of collective progression, extensive server configurations and large collections of mods. Administrators therefore have good reason to be more conservative than players experimenting with a local save.

With 42.21 now officially Stable, communities have a much stronger reason to consider moving their Build 42 servers to the new version.

Project Zomboid's multiplayer infrastructure continues to mature

The update follows several major multiplayer changes introduced during the recent Build 42 cycle.

Build 42.20.3 notably increased the configurable multiplayer limit to up to 254 players and introduced additional improvements for server administration.

Build 42.21 now focuses more heavily on the behaviour and reliability of those persistent worlds: zombie populations, network synchronization, authentication, anti-cheat systems and mod compatibility.