Project Zomboid server patch notes, build by build

The Indie Stone's patch notes cover everything at once: trees, recipes, controllers, and somewhere in the middle the three lines that make a server turn its players away or lose its mods. This page keeps only those lines (client version, saves, mods and Lua, anti-cheat, server settings, multiplayer performance), build by build, newest first, each with its date and a link to the official post.

To set up the server itself (preset, Workshop mods, RAM, bringing an existing world), see the Project Zomboid dedicated server guide. To rent one by the hour, see Project Zomboid on TickServ.

Current stable version: 42.21, promoted to Stable on 28 September 2026. The Indie Stone keeps two separate branches: legacy41 to stay on Build 41, and 42.19 to finish a game started on Unstable 42.19.

What TickServ does with each new build

The server fetches the server image on every start. A stopped server therefore comes back on the latest published version of that image, with nothing for you to do. It follows Steam's Stable branch: no Build 41, no Unstable.
What doesn't move: the ports (16261 and 16262, UDP) and where your world lives (Saves/Multiplayer/), saved on shutdown and restored on the next start.
The image can lag behind Steam. It is built by a third party: on 28 September it stayed on 42.20 for about a day while players' games were already on 42.21. We wrote up that day here.
What we tell you, and when. Every time it starts, the server reads the game version it runs (42.21.0), the one Project Zomboid compares, character for character, with each player's. As soon as it differs from your previous session, even for a plain hotfix, you get a notice in your dashboard, and in your Discord channel if you linked one. If there is one, the last backup from before the change is then set aside, outside the usual rotation, for 14 days (one at a time: the one from before the first change is the one that stays).

42.21 — Stable on 28/09/2026

The first incremental update since Build 42 went Stable. It shipped to Unstable on 23 September and to Stable on 28 September; The Indie Stone says this is now the procedure for every release: Unstable first, Stable after.

Saves: existing 42.20.4 saves should not be affected, according to the Unstable post.
Version mismatch: a player trying to join a server running a different game version now gets a notification telling them so.
Steam authentication: some players could enter dedicated servers without being properly authenticated through Steam, which made SteamID bans useless. Fixed.
Wider anti-cheat: more cheats are now guarded against, and safehouse exploits are closed.
Mods: loadstring and loadstream, disabled in 42.20.4, are re-enabled.
Zombies: duplication in multiplayer has been tackled, along with zombies vanishing when a player left a chunk of the map and came back. The studio says some cases remain, scheduled for the next update.
Server browser: the "Server Update" column now shows the last wipe, not the last restart.
Desync: fewer problems when driving with high ping (around 150 ms and above), and a Z-level desync is fixed.

Sources: Stable post, 28/09, Unstable post, 23/09, full notes on the forum.

42.20.4 — hotfix, 26/08/2026

Security, at a cost for mods: security vulnerabilities are fixed, and as part of that the Lua methods loadstring and loadstream are removed. A mod that used them needs updating; a server that sent code for clients to execute has to use commands instead. This removal was reverted in 42.21.
Hotfixes ship the same day for the 42.19 (42.19.2) and legacy41 (41.78.21) branches.
According to the studio, the update should not break saves.

Source: post of 26/08.

42.20.3 — hotfix, 17/08/2026

Slots: player limit handling is improved, with support for up to 254 players, and an admin can get in when the server is full.
Loading: the client hanging forever on "Loading Map" is fixed.
Memory: several causes of a memory leak that degraded performance until a crash are addressed, along with other memory optimisations.
No save breakage expected.

Source: post of 17/08.

42.20.2 — hotfix, 05/08/2026

Mods and the % sign: files must use %% to display %. A temporary workaround still accepts both, but it will be removed in a future Unstable update. Meanwhile the log flags the files concerned: an error about it comes from a mod that hasn't been updated yet, not from your server.
Nothing else on the server side.

Source: post of 05/08.

42.20.1 — hotfix, 05/08/2026

High-population servers: a performance problem with chunk unloading is fixed; the studio says it caused most of the bugs seen on those servers.
Anti-cheat: Lua checksum validation is stronger.
Build 41 worlds: a B42 server can no longer host a broken B41 world.
Memory: a leak that degraded performance until a crash is fixed.
Players: vehicles no longer vanish when another player disconnects.
Mods: they can now write .json files.

Source: post of 05/08.

42.20.0 — Build 42 goes Stable, 29/07/2026

This is the version that took Build 42 out of Unstable. For a server, two breaks first:

Build 41 saves don't load in Build 42. The studio says so plainly, and offers the legacy41 branch to server owners who want to stay on 41 (their players have to pick it too).
Unstable 42.19 saves don't load in 42.20, because of the new map content. The 42.19 branch lets you finish those games.

Then, on the multiplayer side:

Anti-cheat reworked and re-enabled: antiCheatItem is gone because the check now runs server-side; NoClip and PacketException are still in progress. Better anti-cheat logging, and some false positives fixed.
New settings and tools: the "Show coordinates" server option shows or hides the coordinates line on every connected client, and each player's ping now appears in the Players and Users lists.
Server fixes: special characters in a server name could prevent its files from being created; a server could hang during chunk generation; an exception could occur at dedicated server startup; a player's visited-map data didn't survive a server restart.
Exploits closed: several ways to spawn items, gain XP illegitimately, and copy a dedicated server's map data.
Settings fixed: HidePlayersBehindYou now applies when disabled, and "Enable melee PVP in Factions" no longer turns on firearm PvP too. The cap on the "Zombie count before deletion" sandbox option goes from 500 to 5000.
Mods: a security patch released with this version may affect some mods, and the modding API gets back functionality lost with the 42.14 security patch. XML files are now part of checksum verification.
Logs: more consistent network (ZNet) and packet logging, object pool statistics added, and the "SERVER STARTED" line prints properly again.

Sources: Stable post, 29/07, Build 42 Stable plans, 24/07, B42 checklist, 28/07.

Announced, not out yet

The Indie Stone has announced a "Build 42 Support Update" for the rest of 2026: optimisation, more modding support, and player-requested features. The studio also promises multiplayer improvements throughout Build 42 patching, the release of its mapping tools, and a modding guide. No date has been given.

How this page is kept up to date

Whenever The Indie Stone posts in the game's Steam announcements, we add an entry at the top of this page with its date and link. We only write what the official posts or the full forum notes say: nothing inferred, nothing assumed. A post that doesn't touch servers (a fundraiser, a merch drop) gets no entry. The last revision date is shown at the top of the page.

Host a Project Zomboid server by the hour · The Project Zomboid dedicated server guide