Project Zomboid 42.20.1 hotfix targets multiplayer lag and memory leaks

Project Zomboid's stable branch received hotfix 42.20.1 on August 5, 2026, focused on multiplayer server performance, a memory leak, and several build 41-to-42 transition issues. The update should not break saves. If you hit any bugs, the team asks you to confirm they can be replicated on a fresh save with no mods installed before reporting them on its bug reports forum.

• Improved Lua checksum validation for multiplayer anti-cheat.
• Fixed significant performance problems with chunk unloading on multiplayer servers, which should fix most of the bugs players saw on high-pop servers due to server lag.
• Fixed errors and crashes that could occur when selecting Multiplayer while certain languages were selected.
• Fixed vehicles temporarily disappearing for players after another player disconnected.
• Fixed an issue that allowed broken build 41 worlds to be hosted on build 42 servers.
• Fixed a missing menu for players switching from build 41 to build 42.

• Improved memory usage by reusing discarded world data.
• Fixed a memory leak that could cause performance degradation and crashes over time.
• Fixed a rare exception that could occur during exploration.
• If you still get an out-of-memory error in a new save, submit a bug report with your logs and a profiler video from debug.

• Added support for mods to write .json files.
• Fixed percent symbol handling in translation files; mod translations should now use %% to display a single %.

Join the pinned Project Zomboid Discussions thread for more on the update.