Project Zomboid Build 42.21 Stable Released

Build 42.21 landed on the Unstable branch on 24 September 2026 and was promoted to Stable on 28 September 2026 after community testing confirmed stability. This patch addresses long-standing zombie persistence issues, refines the XXL tree cutaway behavior that frustrated drivers, polishes split-screen play, and expands the anti-cheat system for multiplayer servers. Critically, the Lua loadstring and loadstream methods that were temporarily removed in the 42.20.4 security hotfix have been re-enabled after further investigation resolved the underlying security concerns. This page covers the key changes survivors need to know.

Zombie chunk and duplication fixes

The headline fixes in 42.21 address two problems that haunted hardcore and multiplayer players since Build 42 shipped:

• Zombie disappearance fix: Zombies no longer vanish when a player leaves and re-enters a game chunk. This was especially noticeable in high-zombie-population sandbox settings and impacted the hardcore survival experience. Fixed for both single-player and multiplayer.
• Zombie duplication fix in MP: Related to the chunk issue, multiplayer servers no longer produce zombie duplicates when players move between areas. The team asked players to report any remaining duplication instances.

Project Zomboid Build 42.21 Stable First Look

XXL tree cutaway improvements

A common complaint since the Build 42 launch was the new XXL trees occasionally blocking player movement and hiding structures, especially problematic when driving. Build 42.21 delivers several tweaks:

• XXL trees now cut away better for players inside vehicles
• Trees no longer hide houses and furniture they overhang
• Overall tree transparency has been adjusted for better visibility

The developers describe this as work in progress and welcome feedback on the adjustments.

loadstring and loadstream re-enabled

After the 42.20.4 security hotfix temporarily removed loadstring and loadstream Lua methods, The Indie Stone investigated further and determined the methods could be safely re-enabled. Mod authors whose mods were broken by the removal should find their Workshop items working again in 42.21 Stable. Authors who implemented workarounds may want to verify their mods function correctly with the restored methods.

Welder occupation change

Characters with the Welder occupation now start the game with Welding recipes instead of Blacksmithing recipes. This aligns the occupation bonus with its name and gives Welders a clearer early-game identity for crafting and base work.

Expanded gameplay systems

• 86+ fluid containers can now purify water in appropriate oven types, significantly expanding water processing options
• Washing machines now clean dirty rags, strips, and bandages, a quality-of-life improvement for medical supply management
• Fridges and freezers warm gradually on the day power goes out instead of instant temperature shift
• Refrigeration now applies correctly to food items stored inside a bag placed in a fridge or freezer
• Antibiotics can now be packaged using the pack-in-box crafting recipe
• Explosives now work in basements, opening new tactical possibilities for underground encounters
• Subbiomes on the map no longer generate trees on dirt tiles
• Floorboard stash containers found using annotated maps now have more appropriate names
• Increased brightness on several lamp and illuminated tiles

Split-screen improvements

The small but dedicated split-screen community receives meaningful fixes:

• Read book statuses and XP boosts are no longer shared incorrectly between players
• Fishing now operates as expected in split-screen mode
• Fixed a crash that occurred when sharing a moving vehicle with another player

Multiplayer anti-cheat and server improvements

Build 42.21 significantly expands the anti-cheat system with:

• Various new cheat methods now guarded against
• Safehouse exploits remedied
• Server browser now displays last wipe instead of last restart
• Connect button disabled when no server is selected
• Fixed Steam authentication exploit that allowed players to enter dedicated servers without proper Steam verification, previously prevented SteamID bans from working

High-ping improvements address issues at 150+ ping where players experienced map not loading in front of the car, passenger teleportation, and general multiplayer juddering. A Z-level desync fix better synchronizes player coordinates across the network.

Formalized Unstable testing pipeline

The Indie Stone has clarified their release process going forward: new updates deploy to Unstable first for community testing, potentially receive additional tweaks based on feedback, then move to Stable. The time between Unstable and Stable will vary by update complexity. Unstable is no longer treated as an unofficial Stable branch—it is explicitly a testing channel. Build 42.21 followed this process: community tested on Unstable for four days before Stable promotion.

What this means for stable players

Build 42.21 is the current Stable release. Players on the default branch should have received the update automatically through Steam. Verify your main-menu build string reads 42.21 and enjoy the zombie persistence fixes, XXL tree visibility improvements, and the restored Lua methods. Multiplayer server operators should update promptly to benefit from the expanded anti-cheat protections.

Key takeaways

• Zombie persistence and duplication fixes are the most impactful changes for hardcore and MP players
• XXL tree visibility improvements address a common Build 42 pain point
• Welder occupation now correctly starts with Welding recipes
• Split-screen and multiplayer received substantial polish
• loadstring and loadstream re-enabled—verify Workshop mods after updating
• Unstable is now explicitly a testing channel with formal Stable promotion process

Pair this page with the Build 42 Overview for the Big Glow Up context and Roadmap and Build 43 for what comes next.