# Kotlin v2.4.20-RC2 — Kotlin 2.4.20-RC2

- Product: Kotlin (https://whatsnew.fyi/product/kotlin)
- Vendor: JetBrains
- Date: 2026-08-26
- Version: v2.4.20-RC2
- Original notes: https://github.com/JetBrains/kotlin/releases/tag/v2.4.20-RC2
- Permalink: https://whatsnew.fyi/product/kotlin/releases/v2.4.20-rc2
- Labels: Pre-release

What's New is an index, not a publisher: every entry below links to the vendor's own release notes, which are the authoritative source. Entries are labelled where they are hand-curated sample data, pre-releases, or drawn from a secondary source such as a developer blog.

Reuse: the summaries, labels and curation here are © What's New. Quote freely with attribution and a link back; wholesale republication of the corpus is not permitted — terms: https://whatsnew.fyi/terms. The vendors' own release notes remain their publishers'.

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- **fixed** — Fixed StackOverflowError in CastsOptimization when two nullable local variables are assigned to each other across nested loops in Kotlin/Native
- **fixed** — Fixed a bug that prevented execution of non-local return statements inside lambdas called from when expressions in Compose compiler
- **fixed** — Fixed IllegalStateException caused by @Serializable enum in Kotlin/JS
- **fixed** — Fixed IncrementalCompilationComponents instances not being called anymore
- **fixed** — Fixed Webpack configuration being generated after user defined chunks from the webpack.config.d directory in Kotlin/Wasm

##### Changelog

###### Compiler

- [`KT-88316`](https://youtrack.jetbrains.com/issue/KT-88316) K/N: StackOverflowError in CastsOptimization when two nullable local variables are assigned to each other across nested loops

###### Compose compiler

- [`b/549552317`](https://issuetracker.google.com/issues/549552317) Fixed a bug that, in certain cases, prevented execution of non-local return `statements` inside lambdas called from `when` expressions.

###### JavaScript

- [`KT-88571`](https://youtrack.jetbrains.com/issue/KT-88571) K/JS: "llegalStateException: Internal error: cannot find external signature" caused by  `@Serializable` enum in 2.4.20-RC

###### Tools. CLI

- [`KT-88475`](https://youtrack.jetbrains.com/issue/KT-88475) IncrementalCompilationComponents instances are not being called anymore

###### Tools. Gradle. Wasm

- [`KT-88566`](https://youtrack.jetbrains.com/issue/KT-88566) K/Wasm: Webpack configuration generated after user defined chunks from the webpack.config.d directory