Java 21 to Java 25 on your Minecraft server

Minecraft 26.1 moved the game from Java 21 to Java 25. On our servers you never install Java or pick it: the panel chooses the Java version from your Minecraft version. So "migrating to Java 25" means moving the server to a 26.x version in the JAR Manager, and there are a few things to check around that move.

Checked against Minecraft 26.3 (the latest release when this was written), the Paper documentation and the panel's JAR Manager, October 2026.

Which Minecraft versions use which Java

Mojang's patch notes for 26.1 say "The game now requires Java 25", and its version files give the same answer for every release from 26.1 to 26.3. Releases from 1.20.5 to 1.21.11 use Java 21. The Paper documentation lists Java 21 for 1.20 to 1.21.11 and Java 25 for 26.1 and newer.

26.1 was also the first release with the new year-based version name. After 1.21.11 came 26.1, 26.2 and 26.3, so there is no 1.22.

What this means on your server

• A server on 1.21.x stays on Java 21. Nothing breaks and nothing needs migrating until you choose a 26.x version.
• You cannot choose Java. There is no Java selector and no editable startup command. Under the version picker, the JAR Manager shows a line such as "Runs on Java 25. We switch it for you." and applies it whenever the server is switched or reinstalled.
• Add-ons are checked on the move. The reinstall box in the steps below compares your installed plugins or mods with the new version and tells you how many have no build for it.

Move to a 26.x version

1. Open Backups and press Create backup.
2. Open JAR Manager under More. Pick your Server software and a 26.x Minecraft version. The Java line under the picker should now read Java 25.
3. Press Apply change. The box "Reinstall server?" checks your add-ons against the new version and tells you how many have no build for it. If it offers Disable the N that won't run (kept, not deleted), leave it ticked, as it is by default.
4. Leave Take a backup first ticked, then press and hold the button, which reads Hold to Confirm & reinstall, for about three seconds until it completes. If some add-ons have no build and you unticked the disable box, the button reads Hold to Switch anyway instead, and those add-ons stay enabled.
5. Watch the Console until the server is up. Your world is kept, but configuration files may be reset.
6. Open the Plugins or Mods tab, switch to Installed and press Check for updates, so each add-on moves to a build for the new version.

If the server will not start

Read the end of the Console log first. If the reinstall box listed add-ons with no build, start with those, and the Installed view marks one that failed with Failed to load. Disable it, restart, then find a build for your version. Fix Minecraft Java error exit codes explains the codes the panel can show.

On a server running a modpack, the install box in the Modpacks tab names the Minecraft version the pack installs, so check it there before you pick a different version. Switching software in the JAR Manager removes an installed modpack (its mods stay in the folder), so on a modpack server change the pack version from the Modpacks tab instead.