Build 42 reached the public stable branch on 29 July 2026, after roughly nineteen months on the unstable branch. In the four weeks since, it has had four hotfixes. The most recent, 42.20.4, landed on 26 August and removes two Lua methods that existing mods rely on. Dates, version numbers and quoted text below come from The Indie Stone’s official Steam announcements for Project Zomboid (appid 108600) — nothing here is from a third-party wiki or guide site, and where a patch note is ambiguous, this page says so rather than resolving it. 42.20.4 is still the newest stable hotfix in the feed as of the verification date below; this page will get a new row if that changes.
If you are running mods, that last one matters today. The rest of this page is the timeline.
For what changed between Build 41 and Build 42 as a whole — rather than between 42.19 and 42.20 — see which Build 41 knowledge expired in Build 42.
The five 42.20 releases
| Version | Date | Gap | Where the fixes landed |
|---|---|---|---|
| 42.20.0 Stable | 2026-07-29 | — | Everything: map, balance, controller, MP, SFX, technical |
| 42.20.1 | 2026-08-05 | 7 days | MP performance, memory, % in translation files |
| 42.20.2 | 2026-08-06 | 1 day | % handling again, this time outside translations |
| 42.20.3 | 2026-08-17 | 11 days | Memory leaks again, server player limits, lighting |
| 42.20.4 | 2026-08-26 | 9 days | Security — and the mod-breaking change below |
The one-day gap between 42.20.1 and 42.20.2 is the tell: the percent-symbol fix shipped, then needed a second pass the next day.
42.20.4 removes loadstring and loadstream
This is the only entry on this list that requires action from you rather than just information.
The 26 August note’s fixes are “Fixed security vulnerabilities,” followed by a line for mod
authors: the loadstring and loadstream Lua methods have been removed, and any mod that used
them to run code sent from the server needs to be rewritten. That security fix is one of four
disclosed in 2026 — for the other three, the legacy-branch removals, and the full migration
path, see Project Zomboid’s 2026 security year, branch by branch.
What this means as a player: a mod that has not been updated since 26 August and used either method will break. The announcement does not name affected mods, and this page will not guess at a list. Check your mod’s changelog or its workshop comments before assuming it is fine.
What it does not mean: this is not a save-breaking change. Every one of the five announcements opens with the same line — “While this update should not break saves” — and 42.20.4 is no exception.
The memory leak was addressed twice, and is not declared fixed
This is the pattern that a single patch note cannot show you, and the reason this page exists.
42.20.1 listed, under FIXES: “Fixed a memory leak that could lead to performance degradation and crashes over time.”
42.20.3, twelve days later, listed: “Addressed multiple causes of a memory leak that could lead to performance degradation and crashes over time,” plus “Implemented several memory optimisations.”
Both notes then carry the same follow-up sentence, word for word: if you still hit an out of memory error on a new save, submit a bug report with logs and a profiler video.
Read those together and the honest summary is that memory pressure in 42.20 was attacked in two separate hotfixes and the developers are still asking for reports. That is not the same as “still broken” — 42.20.3 explicitly says multiple causes were addressed. But it is also not “fixed,” and anyone telling you 42.20.3 closed the issue is reading one note instead of two.
The black-and-gray-box problem in 42.20.3 is labelled the same way, and more explicitly: “Reduced instances of black and gray boxes appearing when travelling quickly through the world,” immediately followed by “Additional causes of this issue are still being investigated and will be addressed in a future update.” Reduced, not resolved, and the note says so itself.
The percent-symbol change, and why mod authors got two notes
42.20.1 fixed percent handling in translation files and told mod authors that mod translations
“should use %% to display % characters.”
42.20.2, the next day, extended the fix to files generally, added a temporary workaround so both
the old and new forms keep working for now, and started writing errors into the log so authors can
see what needs changing. It also fixed quick tips that were displaying % as %% — the fix
overshooting into the UI.
The workaround is explicitly temporary. If you maintain a mod, the escaped form is the one that survives.
Where 42.20.0’s effort actually went
The stable release note is long, and its shape is worth stating plainly: multiplayer took the overwhelming majority of it. The MP section runs to well over a hundred entries, against a much shorter list for singleplayer FIXES, SFX and technical work combined.
Several of those MP entries are exploit closures rather than bug fixes — arbitrary item spawning
through animal attachment commands, through modData, illegitimate XP gain, manipulation of foraged
items, and copying dedicated server map data. Anti-cheat was reworked and re-enabled, with
antiCheatItem moved server-side, and the note flags NoClip and PacketException as still work in
progress.
Balance changes in the same release were comparatively few. The ones with numbers attached: the
Sandbox “Zombie count before deletion” ceiling moved from 500 to 5000, and Extinction mode’s
WouldInfectionFactor moved from 1.0 to 2.0. Meat yield from large animals with a butcher hook
went up, without a figure given.
How to use this page
- Running mods and updating today: assume anything using
loadstringorloadstreamis broken until its author says otherwise. This is the only item here with a hard deadline. - Hitting crashes after long sessions: you are in the memory-leak territory that 42.20.1 and 42.20.3 both touched. Update to 42.20.4, then, if it persists, file the report the developers keep asking for — logs plus profiler video from debug.
- Running a server: 42.20.3 raised supported player limits to 254 and added administrator access when servers are full. 42.20.1 fixed the chunk-unloading performance problem that the note says caused “most of the bugs players were getting on high-pop servers due to server lag.”
- Seeing black or gray boxes while driving: known, reduced in 42.20.3, still under investigation by the developers’ own statement. Nothing to do but wait.
- Blocked on a recipe you think you should have: that is a Build 42 crafting-gate question, not a hotfix question — why you can’t craft that recipe covers the gating rules.
Versions and dates on this page are as published by The Indie Stone. When a later hotfix changes any of the above, this page gets the correction and a new revision date rather than a quiet edit. This page tracks the stable branch only — 42.19.2 UNSTABLE and 41.78.21 LEGACY, which shipped in the same 26 August announcement, are out of scope here.
Sources
All five announcements are from The Indie Stone’s official Steam news feed for Project Zomboid
(appid 108600), read 2026-08-27, rechecked against the live feed on 2026-09-13, and re-read in full
on 2026-09-22 to confirm every quoted line and figure above and to check for any newer stable
hotfix — none found; 42.20.4 (26 August) remains the newest. The old steamcommunity.com/.../ announcements/detail/<id> links this page previously cited now redirect to the general
announcements feed instead of the individual post, so the links below point at the equivalent
store.steampowered.com/news permalinks, which still resolve to the specific announcement.
- Build 42.20.0 Stable Released — 2026-07-29
- 42.20.1 STABLE Hotfix Released — 2026-08-05
- 42.20.2 STABLE Hotfix Released — 2026-08-06
- 42.20.3 STABLE Hotfix Released — 2026-08-17
- 42.20.4 STABLE & 42.19.2 UNSTABLE & 41.78.21 LEGACY Hotfixes Released — 2026-08-26
