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Moving a Project to a New Minecraft Version

Update a plugin or mod you already have for a newer Minecraft release: what to ask for, what the Build tab setting really does, and what happens to Java.

It is a code change, so the AI does it

The Minecraft version your jar is built for is written in the project's own build file — pom.xml or build.gradle, and the api-version in plugin.yml. Moving to a newer Minecraft means changing that file, and usually some code with it: methods and classes move between releases.

So this is a request to the AI, not a setting you flip. You do not need a new project — the one you have is updated in place, and everything you had stays in Version History.

Updating the project

1. Open the project and set the switch above the message box to Build.
2. Name the platform and the exact version in one request: "Update this plugin to Paper 1.21.4", or "Move this mod to Fabric 1.21.11". Write it as an instruction — "will it work on 1.21.4?" is a question, and you get an answer instead of a change.
3. The AI rewrites the build file and the calls that no longer fit, and on a plugin or mod project the run compiles the result before it hands back — the reply ends with a Build check line.
4. Press “Build & Export”, download the new jar, put it on the server in place of the old one and restart.

What the Minecraft Version setting does, and does not do

Project Settings → Build carries a Minecraft Version list, which appears once Use global build settings is switched off. It is handed to the AI as the version to write for, so it is worth setting to your server's version — but a version named in your newest message wins over it.

What it does not do is change the jar on its own. Set it, press Build without asking the AI, and you get the same jar again, built for whatever your files say. The build log then tells you so:

> [WARNING] Project Settings → Build say Minecraft 1.21.4, but this project's build files target 1.20.1, so it was built for 1.20.1. To move the project to 1.21.4, ask the AI in chat to update it — the build does not rewrite your code to another version.

Read that line as a to-do, not a failure: the jar is fine, it is simply for the older version.

Newer Minecraft brings newer Java with it

From Minecraft 1.20.5 on, plugins and mods are compiled for Java 21, and from 26.1 on for Java 25. If the project's Java Version is set lower, the build raises it to what that Minecraft version needs instead of failing — so picking Java 17 there does not give you a Java 17 jar for a 1.21 project.

That means the server has to run that Java too. If it does not, it refuses the plugin with UnsupportedClassVersionError, and lowering the setting will not get you round it: update Java on the server. When the Server Console Shows an Error covers the rest of the console messages.

It is a normal run, and a big jump can need several

The update is billed like any other Build run. A jump across several releases can also need repair rounds before it compiles, and a round whose changes are kept is billed on the same run — see Auto-Fix.

Two habits make it cheap: save a version in Version History before you ask, so one click undoes everything; and keep the old jar until the new one has actually started on your server. A plugin that compiles is not yet a plugin that runs.

Try it now: Describe your plugin and see the plan, free and with no account. Open the plugin generator

Where to next

• Not sure which version: Which Servers It Runs On — Every version you can pick, and why 26.1 comes after 1.21.11.
• New jar in hand: Installing It on a Server — Swapping the new jar onto the server.
• Red text on start: Server Console Errors — What a version mismatch looks like in the console.
• If the update broke it: Version History — The way back if the update goes wrong.

17 of 22 in Minecraft Studio · Last checked 12 September 2026 · Previous: Hosting a Minecraft Server