JetBrains announced the release of Kotlin Toolchain 0.12.0 on September 2, 2026. It adds experimental support for publishing Kotlin Multiplatform libraries across multiple targets, along with the ability to build WebAssembly applications ready for use on the web. The release also brings improvements to Android, iOS, and Compose tools, as well as changes to runtime requirements and dependency management.
Publishing Multiplatform Libraries
Library publishing was available in version 0.11 only for JVM libraries. Version 0.12 expands the feature to Multiplatform libraries with the same configuration. Kotlin Toolchain publishes the common API, a file for each platform, source files, and module metadata that helps build tools automatically select the appropriate components.
The support also includes C interop bindings, which are published in common and platform-specific formats, allowing library users to consume the same C interface used for the build without configuring interop manually. JetBrains explains that the result can be used from Gradle projects like any other Multiplatform library. Compose Multiplatform library resources are not yet included in the publishing process, and this point is still being tracked under issue KTC-5698.
From a Wasm Library to a Web Application
wasm-js/app modules can now be built as a ready-to-use web application. Supported capabilities include running Wasm applications with the kotlin run command, customizing index.html and other resources, and fetching transitive npm dependencies from Kotlin Multiplatform libraries.
In practice, this reduces the distance between creating a Wasm component and preparing it as a runnable web application, but it does not change the fact that Wasm support is still provided as a preview in this release.
Improving the Compose Experience and Development Environments
Compose Hot Reload is now supported from the command line through kotlin run --compose-hot-reload-mode, with a faster first reload and reduced resource consumption. The release also supports restarting the application from the DevTools menu and adds an MCP-compliant server through which agents can interact with running applications, reload or run them, display window snapshots, and extract a composable tree.
Android modules and kmp/lib modules targeting Android now receive Compose Preview support, along with Android Lint, Live Edit, Layout Inspector, and navigation and completion related to Android resources. The release also improves the development environment's recognition of Compose resources, as well as updates to Res classes, navigation, and refactoring.
New Requirements and Project Changes
Kotlin Toolchain now sets JDK 17 as the minimum for compiling code, while settings.jvm.release can still be used to target older runtime environments. The minimum Kotlin compiler version has also increased from 2.1.10 to 2.2.20. JetBrains additionally recommends using relative paths to the project root that begin with the // prefix to define local dependencies, while the old relative-path method continues to work for now.
To reduce the number of published files in response to upcoming Maven Central quotas, .asc.sha1 signature files are no longer published. By default, publishing is now limited to the .md5 and .sha1 checksums, with .sha256 and .sha512 available on explicit request.
What Should Developers Know?
Accessing the latest release features requires IntelliJ IDEA 2026.2.1 or later, with the latest Kotlin Toolchain plugin installed. The new default versions include Kotlin 2.4.10, JDK 25, JUnit Platform 6.1.3, KSP 2.3.11, Ktor 3.5.2, as well as updates to DataFrame and Kotlinx.rpc.
Kotlin Toolchain remains in the Alpha stage and is under active development, so the new features—particularly Wasm support and resource publishing—should be treated as non-final. JetBrains says that klibs.io uses Toolchain in production. It is a project built on JDK 21 and Spring Boot 4 with Spring AI, PostgreSQL, and OpenSearch, after converting nine convention plugins into Kotlin Toolchain templates and implementing the Jib and Git Properties add-ons as local plugins.