Kotlin 2.3 Release History and End-of-Life Status

Kotlin 2.3.0 Release Notes

The Kotlin 2.3.0 update, introduces a mix of feature stabilizations, new experimental tools, and compiler improvements across platforms. This Beta release focuses on improving code safety, type checking, and contextual resolution while finalizing several features that have now reached Stable status.

Highlights include:

• Stable support for nested type aliases.
• Exhaustive “when” expressions now validated using data-flow checks.
• New time tracking APIs: kotlin.time.Clock and kotlin.time.Instant.
• A new unused return value checker to detect ignored results in code.
• Enhanced context-sensitive resolution with improved diagnostics.
• Kotlin/Native now enforces type checks on generic boundaries by default in debug mode.
• Kotlin/JVM compilation now uses the Build Tools API (BTA) by default.

IDE Integration

Kotlin 2.3.0 is fully supported in the latest versions of IntelliJ IDEA and Android Studio. No manual plugin updates are required — simply update your build.gradle.kts file to use 2.3.0 as the Kotlin version.

Stable Features

Several previously experimental features are now officially stable in this release:

Language Updates

Kotlin 2.3.0 introduces improvements to the compiler’s handling of context-sensitive resolution and adds a new experimental mechanism for detecting unused return values.

Experimental: Unused Return Value Checker

A new compiler checker warns when a function’s return value (that isn’t Unit or Nothing) is ignored. This helps developers catch logical errors where results are produced but not used.

Example:

fun formatGreeting(name: String): String {
    if (name.isBlank()) return "Hello, anonymous user!"
    if (!name.contains(' ')) {
        // Warning: the result below is ignored
        "Hello, " + name.replaceFirstChar(Char::titlecase) + "!"
    }
    val (first, last) = name.split(' ')
    return "Hello, $first! Or should I call you Dr. $last?"
}
    

To enable this checker, add the following compiler flag to your Gradle build file:

kotlin {
    compilerOptions {
        freeCompilerArgs.add("-Xreturn-value-checker=check")
    }
}
    

You can mark specific files or classes with @MustUseReturnValues to ensure their functions are checked, or suppress warnings using @IgnorableReturnValue for functions where ignoring the result is acceptable.

Experimental: Context-Sensitive Resolution

Kotlin continues refining its context-sensitive resolution feature. In this release:

• The compiler now includes sealed and enclosing supertypes in contextual searches.
• It emits warnings when ambiguity arises due to conflicting declarations.
• Support for code highlighting, analysis, and completion is currently available in IntelliJ IDEA 2025.3 EAP builds.

Kotlin/Native Improvements

Type checks on generic type boundaries are now enabled by default in debug mode. This change ensures better consistency with Kotlin/JVM and Kotlin/JS by throwing runtime ClassCastException errors when invalid casts occur.

fun main() {
    val list = listOf("hello")
    val x = (list as List<Int>)[0] // Throws ClassCastException in debug mode
    println(x)
}
    

Gradle and Build Tools

Kotlin/JVM compilation now uses the Build Tools API (BTA) by default in the Kotlin Gradle plugin. This update modernizes the internal compilation process and allows developers to test BTA integration ahead of full adoption in Kotlin 2.3.20. The feature will be temporarily disabled again in Beta2 for stability testing.

Conclusion

The Kotlin 2.3.0 release brings a significant step forward for developers working with Kotlin across multiple platforms. With stable features, better compiler checks, and enhanced build tooling, it offers a more predictable and safer coding experience.

As the Kotlin team continues refining the Beta series, developers are encouraged to try out these updates, report issues, and prepare for the upcoming stable 2.3.0 release.

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