Incompatible Gradle and Kotlin comes with IntelliJ IDEA 2025.3.1

IntelliJ Platform
1

I created a new plugin project:
With: JDK: 25 Oracle OpenJDK 25
and: Add sample code

And dependencies:

  • XML
  • Java
  • Kotlin

I then pressed [Create]

I got: Gradle ‘SimpleSimulaPlugin’ build scripts found, I pressed [Load Gradle Project]

I got: Found invalide Gradle JVM configuration
JDK 25 isn’t compatible with Gradle 9.0.0. Please fix JAVA_HOME environment variable.

After quite a while I got: A seemingly ok project.

I then pressed: [Run IDE with Plugin]
I got a lot of errors:

  • Project JDK is not defined
  • Kotlin: Unknown JVM target version: 25
    Supported versions: 1.8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24
  • Incompatible Gradle JVM
  • The autoGenerated: MyMessageBundle is full of errors:
    • e: file:///C:/GitHub/WorkSpaces/Intellij/SimpleSimulaPlugin/src/main/kotlin/org/simula/simplesimulaplugin/MyMessageBundle.kt:14:22 This annotation is not applicable to target ‘type usage’. Applicable targets: field, local variable, value parameter, expression

I use:
IntelliJ IDEA 2025.3.1
Build #IU-253.29346.138, built on December 18, 2025
Source revision: 9478cb03fae44
Runtime version: 21.0.9+1-b1163.86 amd64 (JCEF 137.0.17)
VM: OpenJDK 64-Bit Server VM by JetBrains s.r.o.
Toolkit: sun.awt.windows.WToolkit
Windows 11.0
GC: G1 Young Generation, G1 Concurrent GC, G1 Old Generation
Memory: 2048M
Cores: 16
Registry:
ide.experimental.ui=true
Non-Bundled Plugins:
org.jetbrains.completion.full.line (253.29346.138)
intellij.webp (253.28294.218)
Subversion (253.29346.170)
DevKit (253.29346.50)
com.intellij.spring (253.29346.157)
com.jetbrains.restClient (253.29346.170)
intellij.jupyter (253.29346.138)
org.jetbrains.plugins.kotlin.jupyter (253.29346.138)
org.jetbrains.idea.maven (253.29346.138)
com.intellij.mcpServer (253.29346.142)
Kotlin: 253.29346.138-IJ

2

Hi, JetBrains IDEs 2025.3 still use JBR 21 runtime and you will not be able to use JDK 25 classes and bytecode target for plugins until we switch to 25.

The plan is to update runtime to 25 in 2026.1 versions starting with EAP

Kotlin: Unknown JVM target version: 25
3 
Any idea when that will be?
4

EAP 2026.1 starts approximately in the middle of January 2026