The Indie Stone moved Build 42.21 from Project Zomboid’s Unstable beta to the public Stable branch on 28 September 2026, five days after it entered Unstable testing on 23 September. The build is narrow by design — the studio calls it an incremental update — and its headline items are the two multiplayer complaints that have dominated player discussion since Build 42 went stable: zombies that disappeared when a player left and re-entered a “chunk” of the world, and zombies that duplicated on multiplayer servers. It also takes a second pass at the XXL trees added with the Build 42 map overhaul, and restores two Lua commands the studio disabled in its previous hotfix.
What changed: Build 42.21 went Stable on 28 September, fixing zombie despawn on chunk re-entry in both single- and multiplayer, tackling MP zombie duplication, and re-enabling the
loadstringandloadstreamLua commands. Why it matters: the despawn bug hit large zombie-population saves hardest, so long-running single-player worlds and busy servers see the biggest practical difference. Who should care: players running high-population sandbox worlds, dedicated-server admins, and modders whose tooling depended on the two restored Lua commands.
42.21 at a glance
| Area | What 42.21 changes | Practical effect |
|---|---|---|
| Zombie despawn | Zombies no longer disappear after a player leaves and re-enters a world chunk, in SP and MP | Long sessions in dense areas stop quietly draining the horde |
| MP duplication | “Several issues of zombie duplication in MP” fixed outright, plus one additional case | Server population counts drift less over a session |
| XXL trees | Cutaway improves for players in vehicles; trees no longer hide the houses and furniture they overhang; transparency adjusted | Driving sightlines are clearer, by the studio’s own description still in progress |
| Lua modding | loadstring and loadstream re-enabled after being disabled in the 42.20.4 hotfix | Mods and admin tooling that relied on them should work again |
| Anti-cheat | Expanded anti-cheat system; new cheats guarded against; safehouse exploits remedied | Fewer server-side abuse routes |
| Steam auth | Fixed players entering dedicated servers without correctly authenticating via Steam | SteamID bans work again on affected servers |
| High-ping driving | Driving fixes at ping around 150 ms or above; RakNet throughput scaling repaired | Less map pop-in ahead of the car, fewer passenger teleports |
| Split-screen | Crash when both local players share a moving vehicle fixed; read-book status and XP boosts no longer shared incorrectly | Same-screen play is usable again at the point it broke |
The despawn fix, and what it does not promise
Both Project Zomboid posts describe the same failure from slightly different angles. The Stable announcement frames it as “issues in which zombies would disappear after a player left and re-entered a ‘chunk’ of the game world in both SP and MP,” while the earlier Unstable post supplies the detail that matters most for judging who was actually hurt: the problem was “particularly obvious in larger zombie population games and as such impacted a lot of our hardcore players.”
That population qualifier is the useful part. A chunk in Project Zomboid is a slice of the world the game loads and unloads as you move; the bug meant that unloading and reloading a slice could lose its zombies, which is nearly invisible in a low-density sandbox and very visible in a horde-population one. The studio says the fix required finding the cause at its root rather than papering over the symptom, and it now applies to single-player and multiplayer alike.
It is not a closed file, and the studio says so plainly. The Stable post reports that “there are still some instances of this which we have on our radar and will be fixed in our next update.” Read 42.21 as a large reduction in how often the despawn happens, not as a guarantee that your horde is safe.
The duplication half of the story carries the same caveat. The Unstable post says the issues “have also been tackled,” then asks players to keep watching: “we’d ask you to be on the look out for any other instances you spot once Unstable is live.” The full patch notes list “Fixed additional case of zombie duplication” among a long run of multiplayer entries. Taken together, the two posts describe a class of bug narrowed rather than a class of bug proven dead.
XXL trees: clearer sightlines, still unfinished
The XXL trees arrived with the Build 42 map work and quickly became a driving problem. The studio’s own summary of the feedback is that the trees were “occasionally getting in the way of the player — especially when driving,” and 42.21 changes their cutaway behaviour in three named ways: they “now cutaway better for players in vehicles,” they “no longer hide houses and furniture they overhang,” and their “overall transparency has been adjusted for better overall visibility.”
The studio does not present this as finished. The Stable post says the work “will make your life easier, but is a work in progress and will receive more love in future,” and in the official patch thread a studio account answered a follow-up question on the same point by saying the trees “are a work in progress, and will be modified further.”
Players have already reported that the new cutaway over-applies. In the patch thread one poster asked whether it is now intended behaviour that “when I get into my car ALL XXL trees are cutoff” — a player observation about the new behaviour, not a studio statement of intent. The Indie Stone’s reply on that post, quoted above, says the trees are still a work in progress rather than confirming the over-application as intended. Worth knowing before you judge the change on your first drive.
loadstring and loadstream come back
In the 42.20.4 stable hotfix The Indie Stone disabled the loadstring and loadstream Lua commands to address security vulnerabilities. Build 42.21 reverses that. The studio’s wording is direct: “After investigating further into the security issue, we’ve decided to re-enable those commands. Sorry for the disruption, modders/server admins!”
The reason the reversal matters is scope. Those commands are not a small surface for mod authors or server operators, and disabling them mid-branch broke tooling that had been working for years. The Stable post also thanks the people who reported the underlying security problem, naming Scribl (Boris) and Rasmus Moorats (nnsee) for “their aid in flagging security vulnerabilities that were fixed in 42.20.4.”
Multiplayer beyond the horde
The despawn and duplication fixes are the headline, but the multiplayer changelist runs much wider. The anti-cheat system was expanded, with “various new cheats now guarded against” and safehouse exploits remedied. A Steam authentication exploit was closed — the notes describe it as “an issue where players could enter dedicated servers without correctly authenticating via Steam, which prevented SteamID bans,” which is the difference between a cheater being bannable and being able to return.
Server-browser behaviour changed in two small, practical ways: “Server Update will display the last wipe, not the last restart,” and “Connect” is now disabled when no server is selected.
Driving on a bad connection got specific attention. The studio says it “fixed issues when driving with high ping (~150+) so instances of the map not loading in front of the car, passenger teleportation and general MP-associated juddering will be improved,” and separately that it fixed the RakNet reliable data stream failing to scale throughput at a ping of roughly 150 ms. A Z-level desync fix is also in, described as better synchronising player coordinates.
One dedicated-server operator posting in the patch thread reported running a server with 60–90 players at peak and said several areas they had reported — including the texture-loading issue where assets appeared only as shadows, and the world-reuser thread mutating map objects — appeared to be addressed in the list. That is a player assessment posted in the thread, not a studio confirmation, and that operator said they still intended to verify each one against the new build.
Balance and quality-of-life
The balance pass is modest but touches routines most survivors run daily. Washing machines now clean dirty rags, strips and bandages; fridges and freezers warm gradually on the day the power goes out, and refrigeration is applied correctly to food in a bag inside one; characters with the Welder occupation start with Welding recipes instead of Blacksmithing recipes; explosives now work in basements; antibiotics can be packaged with the “pack in box” crafting recipe. The count of fluid containers usable for water purification in the appropriate oven type rises by 86.
Two items are worth flagging for accuracy. The pathfinding change — characters avoid walking over farming plants where possible — comes with an explicit studio clarification in the patch notes: “Player characters do not damage crops when they step on them. This is purely a cosmetic change.” And characters now automatically re-equip items after exercise, which removes a small repeated inventory chore.
Split-screen gets its two worst bugs fixed
The studio acknowledges its split-screen audience is small, and the changelist reflects a targeted rather than broad pass. The game crash that occurred “when the local and co-op player are both in the same moving vehicle” is fixed, read-book status and XP boosts are no longer shared incorrectly between split-screen characters, fish bubbles stop disappearing when a second character joins, and Player 1 can fish even when Player 2 is far away. Split-screen controls also recover after a gamepad disconnect.
What this means for your save
Existing savegames on Build 42.20.4 “should not be affected by this update,” per the studio, but it still recommends backing up a save manually before loading it on the beta branch — the caveat exists because 42.21 went through Unstable first, and Unstable is where save-breaking surprises tend to surface. If you do hit a bug, the studio’s stated process is to confirm it reproduces on a fresh save with no mods installed before reporting it, and it notes that bug reports posted outside the official forums are likely to be missed.
The release rhythm behind the patch
42.21 is also a statement about how The Indie Stone intends to ship from here. The Stable post calls the Unstable-first process “the standard procedure for all releases” going forward: a build goes to Unstable, players test it, the studio makes changes, and it then goes to Stable — so long as the community reports nothing major. In this instance it reports that nothing major came back, so the go button was pressed.
The Unstable post adds the intent behind the cadence: the studio is “trying to move faster, with Unstable not acting as an ‘unofficial Stable’, but instead being used for testing and feedback.”
Not everyone reads it that way. In the patch thread one poster argued the sequence is backwards — that Build 42.20 reached Stable carrying new, untested features, leaving the Unstable branch more stable than the stable one. A studio account agreed with the criticism and endorsed the direction: “You’re right, and this is the strategy we’re moving toward. Please help us bake and prove it stable!” That reply is the clearest statement available of why 42.21 landed five days after it entered testing rather than five weeks.
For readers weighing this patch against how other survival sims handle the same class of problem, our 7 Days to Die V3.3.0 guide covers how another horde-survival game rebalanced its inventory and base design in the same month, and the survival-craft primer breaks down the gather-build-survive loop these patches are all ultimately tuning.