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JetBrains released Kotlin 2.3.0 on December 16, 2025. The release stabilizes nested type aliases and data-flow-based when exhaustiveness, enables explicitly typed returns in expression bodies by default, and updates Kotlin’s JVM, Native, Wasm, JS, and build tooling. It is no longer the latest Kotlin release: JetBrains’ release history lists Kotlin 2.4.20, released September 7, 2026, as the latest release in the 2.4 line. Treat 2.3.0 as an upgrade reference for projects that need that version, not as the current default target.
What’s new in Kotlin 2.3.0?
The release adds language and platform changes across Kotlin/JVM, Kotlin/Native, Kotlin/Wasm, Kotlin/JS, Gradle integration, the Compose compiler, and the standard library. The most visible language changes affect type aliases, exhaustiveness checks, and return statements.
Language and compiler changes
- Nested type aliases are Stable. A type alias can now be declared inside another declaration, allowing related types to be grouped with the code that uses them.
- Data-flow-based exhaustiveness checks for
whenare Stable. The compiler can use information from data flow when determining whether awhenexpression covers all cases. - Explicitly typed returns in expression bodies are enabled by default. This permits
returnstatements in expression-bodied functions when the function has an explicit return type. - An unused return-value checker is introduced. It can help identify calls whose returned values are discarded.
- Context-sensitive resolution changes. The release adjusts how the compiler resolves references in context-sensitive situations.
Kotlin/JVM
Kotlin/JVM can generate classes using Java 25 bytecode. This is a bytecode-target capability; it does not by itself establish that every Java 25 API is available to a project. Check the JDK used to compile and run the application, along with any library or deployment requirements.
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Kotlin/Native and Kotlin Multiplatform
- Swift export improves, including support for native enum classes and variadic function parameters.
- C and Objective-C library import moves to Beta. Beta is not a stability guarantee; compatibility limitations can remain. The documented
@ExperimentalForeignApiopt-in still applies to some interop APIs. - JetBrains reports that Kotlin/Native release-task builds can be “up to 40% faster, depending on the project size,” with the improvement especially noticeable in Kotlin Multiplatform projects targeting iOS. This is JetBrains’ benchmark claim, not a promise for an individual project.
Kotlin/Wasm, Kotlin/JS, and the standard library
- Kotlin/Wasm: fully qualified names and a new exception-handling proposal are enabled by default. The release also adds compact storage for Latin-1 characters.
- Kotlin/JS: experimental suspend-function export, a
LongArrayrepresentation, and unified companion-object access are among the changes. - Standard library: time-tracking functionality becomes Stable, while UUID generation and parsing are improved.
See JetBrains’ Kotlin 2.3.0 release notes for the complete feature list and platform details.
#1 Best Overall
Check Gradle and Android Gradle Plugin compatibility
Kotlin 2.3.0 is fully compatible with Gradle 7.6.3 through 9.0.0, according to JetBrains. Newer Gradle releases may still work, but the release notes warn that users can encounter deprecation warnings or lack support for some newer Gradle features.
For Android builds, the release notes specify Android Gradle Plugin (AGP) 8.2.2 as the minimum and 8.13.0 as the maximum supported version for Kotlin 2.3.0. Check the Kotlin and AGP documentation for your exact configuration before changing either version.
Rank #2
| Build configuration | Kotlin 2.3.0 guidance |
|---|---|
| Gradle | Fully compatible with 7.6.3 through 9.0.0, per JetBrains’ release notes. Newer versions may work, with possible warnings or missing support for new Gradle features. |
| Android Gradle Plugin | Release-note range: 8.2.2 minimum through 8.13.0 maximum. |
| AGP 9.0.0 built-in Kotlin support | In the described setup, the Kotlin kotlin-android plugin is no longer necessary and can cause a configuration error. |
| Kotlin Multiplatform Android target with AGP 9 | Google’s com.android.kotlin.multiplatform.library plugin and its android block are the direction identified by the release documentation. |
The AGP 9 details are configuration-specific, not a blanket instruction to remove a plugin from every Android project. Use the Kotlin Gradle configuration guidance and current Android documentation to determine the correct setup.
What can break when upgrading?
The Kotlin 2.3.x compatibility guide describes changes from Kotlin 2.2 to 2.3 and distinguishes source, binary, and behavioral compatibility. It does not cover how Kotlin code appears to other programming languages. Review these changes against the project’s compiler flags, build system, and deployment targets before upgrading.
Language-version settings
- Compiler support for
-language-version=1.8is removed. - Language version 1.9 is unsupported on non-JVM platforms.
The compatibility guide says Kotlin 2.2 warned about these configurations, while Kotlin 2.3.0 turns them into errors. Search build scripts and compiler arguments for affected settings and update them where appropriate.
Ant builds
Support for the Ant build system is removed. Projects that still rely on Ant need a different build setup to use Kotlin 2.3.0.
Apple deployment targets and Intel targets
Kotlin/Native raises its minimum supported Apple OS versions in 2.3.0:
| Platform | Previous minimum | Kotlin 2.3.0 minimum |
|---|---|---|
| iOS | 12.0 | 14.0 |
| tvOS | 12.0 | 14.0 |
| watchOS | 5.0 | 7.0 |
JetBrains documents an override for older iOS and tvOS minimums, but warns that successful compilation is not guaranteed and the override may break builds or apps at runtime. Do not treat it as a safe way to preserve support for older operating systems.
Best Value
The macosX64, iosX64, tvosX64, and watchosX64 targets are demoted to support tier 3. JetBrains says CI testing and source or binary compatibility across compiler releases are not guaranteed at that tier. The 2.3.0 release page also described eventual removal in 2.4.0; because the 2.4 line has shipped, consult current target-support documentation rather than assuming that older forward-looking plan still describes present support.
For the full migration scope, use the Kotlin 2.3.x compatibility guide alongside the release notes.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.How do I update to Kotlin 2.3.0?
JetBrains’ version-specific release guidance is to change the Kotlin version in the project’s build scripts. The Kotlin plugins supporting 2.3.0 were bundled in the latest IntelliJ IDEA and Android Studio versions at the time of that release; that statement does not identify which IDE builds are current in 2026.
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- Check the target first. Confirm that your project needs Kotlin 2.3.0 rather than a later supported line, and check its Gradle, AGP, language-version, build-system, and Apple-target requirements.
- Update the Kotlin version in your build scripts. Change the version declaration used by your project’s build configuration to
2.3.0. The exact file and syntax depend on how the project declares plugins and dependencies. - Use a compatible IDE and plugins. Check current IntelliJ IDEA or Android Studio documentation for Kotlin plugin support rather than relying on the 2025 release-page wording.
- Build and test all relevant targets. Address compiler errors from removed language-version settings, verify Android plugin configuration, and test deployment targets and interop code that the upgrade affects.
JetBrains documents the release and its update context on the Kotlin 2.3.0 release page. For the current position of 2.3.0 in the release line, see the Kotlin release history.
Should you move to Kotlin 2.3.0 now?
Choose based on the project, not on the release number alone. Kotlin 2.3.0 may be relevant when you need its stabilized language features or platform changes and your build and deployment targets fit its compatibility constraints. If you are starting an upgrade today, first assess whether the project should target a later supported Kotlin line: JetBrains’ release history lists Kotlin 2.4.20 as the latest release in the 2.4 line as of October 4, 2026.
Quick Recap
- Compare the feature you need with the migration work it requires.
- Check the project’s Gradle and AGP versions against the documented range.
- Review Apple OS minimums and the support tier of any Intel Apple targets.
- Find affected language-version flags and any remaining Ant build usage.
- Confirm whether 2.3.0 or a later supported line is the right destination for this project.
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