Build 41 and Build 42 use completely different, incompatible save formats — there is no official conversion tool, and there never will be one, since the internal data structures for crafting, item definitions and terrain changed too fundamentally to bridge. Your B41 world isn’t deleted by switching branches, but if you don’t back it up before doing anything else and then let something overwrite it, it’s gone for good. Do the backup first, always.
Build 42 is no longer a beta you opt into
Version 42.20 replaced Build 41 as the default Stable branch after 19 months of public testing. New servers and new Steam installs get Build 42 automatically now — Build 41 is the one you have to deliberately choose, via the “legacy41” beta branch, not the other way around as it was before July 29th.
Worth knowing if you were testing on the old Unstable branch: saves from Build 42 Unstable versions up to 42.19 are also incompatible with 42.20 Stable, because of additional content added for the stable release. A 42.19 world is in exactly the same situation as a Build 41 one — it needs its own backup and can’t be opened in 42.20 either.
Migrating to Build 42
Zomboid/Saves/Multiplayer/<servername>/. Most host panels have a one-click cloud backup option; use it, or pull the folder yourself over SFTP..ini file, B42 requires a backslash before each Mod ID on the Mods= line — new syntax that didn’t exist in B41. Bringing over your old B41-format mod list without adding the backslashes is the single most common reason mods fail to load after migrating.Staying on Build 41 is a completely reasonable choice
If your community is deep into an active B41 run, or your server depends on mods that haven’t been ported yet, there’s no pressure to move immediately. Steam kept Build 41 available permanently through the “legacy41” beta branch — pin your server to it, and a future accidental reinstall can’t pull Build 42 out from under your save.
Every player needs to select “legacy41” under Game Version & Betas in their own Steam client too, or they’ll hit a version mismatch trying to join. There’s no partial compatibility between builds in either direction.
B42 needs more RAM at the same player count
The larger map, deeper crafting simulation and new animal husbandry system (livestock and wildlife, both individually tracked) all add continuous overhead beyond what B41 needed at the same player count.
Most host panels let you change a server’s RAM allocation directly rather than requiring a full rebuild — check yours before assuming you need to migrate to a new plan entirely.
See our full RAM requirements breakdown for exact figures by group size.
