Data basis: The Indie Stone’s official Steam announcements for Project Zomboid (appid 108600), read 2026-08-27 via the Steam news API. Dates, version numbers and quoted text below come from those announcements and are exact as of that read. Nothing here is from a third-party wiki or guide site. Where a patch note is ambiguous, this page says so rather than resolving it.
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.
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 lists two fixes. The first is “Fixed security vulnerabilities.” The second spells out the cost:
Mod makers should be aware that as part of this fix, the loadstring and loadstream methods have been removed. If your mods used these methods you will need to update your mods.
The announcement gives one migration path and one escape hatch. If you were using these methods to
run code sent from the server, the developers say you “will need to create the necessary methods
and call them by sending the appropriate commands.” If that does not fit your case, they ask you to
report it in the #mod_portal channel of the official Discord and explain how you were using them.
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.
What could not be confirmed
- Which specific mods 42.20.4 breaks. The announcement names none, and this page will not compile a speculative list.
- Whether the memory leak is resolved. Two hotfixes addressed it; the developers still solicit reports. Both facts are stated above; neither settles it.
- The size of the balance changes without figures — the butcher-hook meat increase is described as “increased” with no value.
- Anything about 42.19.2 UNSTABLE or 41.78.21 LEGACY beyond their appearing in the same 26 August announcement title. This page tracks the stable branch only.
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.
Sources
All five announcements are from The Indie Stone’s official Steam news feed for Project Zomboid (appid 108600), read 2026-08-27.
- 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
