Direct answer

Build 41 saves do not migrate to Build 42, and 42.19 saves do not migrate to 42.20 Stable. Preserve those worlds on legacy41 or 42.19. Back up a 42.20.x world before a same-line hotfix and keep the untouched copy until it loads cleanly.

Do this first

  1. Identify the version that created the world.
  2. Copy the save before launching another branch.
  3. Select legacy41 for Build 41 or 42.19 for an unstable 42.19 world.
  4. Use a new world for Stable Build 42.20 content.
  5. Match every multiplayer client to the server branch.

Compatibility by source version

The source version is decisive. A world does not become compatible just because the target branch is newer.

  • Build 41 → legacy41: stated preservation path.
  • Build 41 → 42.20: not compatible.
  • 42.19 → 42.19 branch: stated preservation path.
  • 42.19 → 42.20 Stable: not compatible because map content changed.
  • 42.20.x → later 42.20.x: back up first and read the hotfix notice.

Multiplayer adds another boundary

A server world, server executable, client executable, and mod set can each be on a different version. Confirm all four before treating a failed load as save corruption.

  • Record server and client versions.
  • Preserve server save and configuration together.
  • Test an update with a copy, not the only world.

What not to do

Do not overwrite the only copy of a long-running world or repeatedly open it across branches hoping for conversion. The safe outcome may be separate worlds on separate branches.

FAQ

Quick answers

Can a Build 41 save be converted to Build 42?

The official release says Build 41 saves are not compatible. Keep that world on legacy41.

Will a 42.19 save work on 42.20?

The developer says no because additional map content was added; use the preserved 42.19 branch.

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.