Kotlin v2.4.21 released!

NewsBot · 8 October 2026 12:25

Kotlin v2.4.21 has been released.

Changelog

Backend. Wasm

KT-89267 K/Wasm: calling a (T) → R lambda with an argument that isn’t a T traps instead of throwing ClassCastException

JVM. Reflection

KT-89280 NoSuchElementException in argumentsMakeSenseOnlyForMutableContainer for Java non-static inner class of generic outer class

KT-80710 Reflection: change KCallable representation to avoid dependency on K1

JavaScript

KT-89449 Kotlin/JS: Member names no longer minified in production

KT-89363 KJS. Regular class with companion can’t extend external class

Tools. Compiler plugins. Serialization

KT-89275 Kotlin/Wasm: Invalid Wasm is emitted for a @Serializable generic class with a class upper bound

Tools. Gradle. Native

KT-89285 SwiftPM import results in flooded log

KT-86251 K/N: Flaky linkDebugTestLinuxX64 failure with “truncated or malformed archive” on libstdlib-cache.a

Tools. Scripts

KT-89247 Kotlin Script: NoClassDefFoundError on 2nd execution with transitive dependency from imported script

KT-89220 JSR-223: generic Java bindings break all subsequent eval() calls

KT-88458 Audit closeable resource usage

KT-88453 VirtualFileScriptSource.text leaks an unclosed file stream — script source file handle held until GC, blocks file deletion on Windows

Link: Release Kotlin 2.4.21 · JetBrains/kotlin · GitHub