Project Zomboid: How to Continue a Build 41 or Unstable 42.19 Save

Choose the branch for the save you intend to finish

To continue an old Project Zomboid run after the Build 42 Stable transition, first distinguish a Build 41 save from an Unstable 42.19 save. The Indie Stone provides different Steam branches for them because Build 41 saves do not work in Build 42, and 42.19 saves do not work in 42.20 after the map additions. A branch choice preserves access to the old version; it is not a save-conversion tool. [1]

Select legacy41 to continue a Build 41 world

For a Build 41 run, open the game’s Steam library entry, right-click it and select Properties. In Game Versions & Betas, select legacy41. The developer specifically includes Build 41 server owners and online players in this route, so a group staying on its old game should coordinate the branch choice rather than assuming the default Stable update will keep that world compatible. [1]

Steps

1. Right-click Project Zomboid in Steam → Properties → Game Versions & Betas → legacy41 for the Build 41 save. [1]

Select 42.19 for an unfinished Unstable 42.19 run

For the separate case of an Unstable 42.19 run, use the same Steam Properties menu but choose 42.19 instead. The developer introduced this branch specifically so those games could be finished after 42.20 arrived. Do not substitute legacy41 simply because the save is older than the current Stable release; the two options target different generations of the game. [1]

Steps

1. Choose 42.19 under Game Versions & Betas if the unfinished save was created on Unstable 42.19. [1]

Separate compatibility branches from current Stable fixes

The later 42.21 announcement describes the release process as an Unstable test followed by changes if needed and eventual promotion to Stable. Staying on an old compatibility branch is therefore a decision to continue the old run, rather than a claim that it automatically contains every current Stable improvement. In 42.21, for example, zombie population bugs and XXL-tree visibility received changes, with some cases still acknowledged as work in progress. [2]