Direct answer

Use Steam Library → Project Zomboid → Properties → Betas. Select legacy41 for a Build 41 world, the preserved 42.19 option for a 42.19 world, or the default Stable line for new Build 42.20.x worlds. Back up before changing anything.

Do this first

  1. Close Project Zomboid and back up the world.
  2. Open the game's Properties in Steam.
  3. Choose Game Versions & Betas.
  4. Select the branch matching the save's source.
  5. Wait for Steam, then confirm the version before loading.

Which branch belongs to which world

The release provides two preservation lanes: legacy41 for Build 41 and 42.19 for the last unstable world. Stable is for current 42.20.x play, not a converter.

  • legacy41: finish or revisit Build 41 worlds.
  • 42.19: preserve a world made on that unstable build.
  • Stable: create and maintain current 42.20.x worlds.

Keep mods separated too

A Workshop item may target Build 41, Build 42, or both. Use separate presets and record the working collection for each branch. A correct branch with the wrong mod set can still fail.

Verify before Continue

Check the displayed version, selected Steam branch, and save's source. In multiplayer, repeat the check on the dedicated server and every client.

FAQ

Quick answers

Does legacy41 delete Build 42 saves?

The branch changes the installed game version. Keep separate backups and do not open a world with a version that did not create it.

Can friends use different branches on one server?

No. Server and clients need the same game line and compatible exact version.

Evidence log

Sources checked

Official sources establish universal facts; forum and specialist sources are used for symptoms, vocabulary, and cross-checking.

OfficialProject Zomboid Build 42.20 Released

Official Stable status, legacy41 instructions, and the explicit Build 41/42.19 save boundaries.

OfficialB42 Checklist

Official pre-launch checklist confirming that Build 41 saves do not carry into Build 42.