KotlinConf 2026 Brings Official VS Code Extension, Stable Context Parameters in Kotlin 2.4-RC, and New Productivity Data
JetBrains unveiled an official Kotlin extension for VS Code in alpha, previewed Kotlin 2.4-RC feature stabilizations, and published research showing Kotlin development cycles are 15–20% shorter than Java.
Overview
JetBrains held KotlinConf 2026 in Munich on May 21–22, delivering a keynote that covered language improvements arriving in Kotlin 2.4, an official Kotlin extension for Visual Studio Code entering alpha, and a data-backed study showing Kotlin engineers complete development cycles 15–20% faster than their counterparts working in Java. The announcements reinforce a pattern visible across recent Kotlin releases: broader tooling reach, deepening Kotlin Multiplatform adoption, and incremental stabilization of features that were experimental in earlier releases.
The Machine Herald previously covered the Kotlin 2.3.20 release, which brought name-based destructuring and a Kotlin/Wasm runtime that runs up to 4.6x faster.
Official VS Code Extension in Alpha
The headline tooling announcement at the conference was the alpha release of an official Kotlin extension for Visual Studio Code. According to the Kotlin Blog, the extension — named Kotlin by JetBrains — provides “code completion, diagnostics, navigation, quick fixes, formatting, and project import.”
The extension is powered by the Kotlin Language Server, which JetBrains describes as being built on IntelliJ IDEA’s code-insight infrastructure: “Kotlin-aware features in VS Code are backed by the same foundation we use for Kotlin support in IntelliJ IDEA.” The language server is hosted on GitHub as a partially closed-source project; the repository notes that “the language server is based on the most recent IntelliJ IDEA version and proprietary parts of JetBrains Air and Fleet products, making it partially closed-source.”
The extension is available on the Visual Studio Marketplace under extension ID JetBrains.kotlin-server. It is compatible with any editor that supports the Language Server Protocol, not just VS Code. JetBrains described the launch as “part of our ongoing work to support Kotlin developers across different tools and workflows,” and explicitly flagged the release as an alpha requiring user feedback.
This build on earlier VS Code Kotlin efforts: InfoWorld reported that JetBrains introduced a Java to Kotlin converter extension for VS Code on February 19, 2026. Alina Dolgikh, Kotlin product manager at JetBrains, said at that time that “developers can expect a reliable conversion that respects Kotlin idioms and syntax requirements.”
Kotlin 2.4-RC: Context Parameters and Explicit Backing Fields Graduate to Stable
The KotlinConf keynote outlined the Kotlin 2.4 release candidate’s feature set, with context parameters and explicit backing fields moving from experimental to stable. Both features had been under development since earlier Kotlin 2.x releases. Context parameters enable expressive APIs by allowing functions to declare contextual requirements; explicit backing fields give developers direct control over the underlying storage of a Kotlin property.
Starting with Kotlin 2.4, the Kotlin standard library will carry an “18-month security support policy,” according to the keynote blog post, with security fixes backported across active release lines. The keynote also noted that Swift Export — Kotlin’s mechanism for generating Swift-compatible APIs from Kotlin/Native code — is moving to Alpha in the 2.4 release.
On the toolchain side, collaboration with Google on Kotlin Symbol Processing achieved a “17%” reduction in execution time for complex builds, per the keynote post. For Kotlin/Native specifically, a rewrite of coroutine lock handling in R8 delivered up to “50%” savings on composed performance benchmarks. Build times on Kotlin/Native also improved by “25%” when measured against the Google Docs codebase.
Productivity Study: 15–20% Faster Cycles Than Java
Alongside the conference, JetBrains published a research study examining development speed. According to the Kotlin Blog, the analysis covered “telemetry from IntelliJ IDEA Ultimate over a 20-month window, from November 2023 to June 2025, covering roughly 320,000 developers and 28 million development cycles.”
The study defines a cycle as “the wall-clock time from the first edit of a source file after a push to the next push on that file” and “compared the same developers before and after their migration from Java to Kotlin, against developers who stayed on Java.” The headline result: “on comparable work, Kotlin developers spent about 15%–20% less time than developers working in Java.”
Broken down by task size, the study found that Kotlin cycles were on average about 15.7% shorter for small tasks, about 20.3% shorter for medium tasks, and about 15.1% shorter for large tasks. Java projects showed a contrasting trend: “Java projects slowed down over the 20-month window. Cycles became 9%–17% longer as codebases grew.”
Ecosystem and Multiplatform Growth
The keynote cited broader adoption figures: “92%” of professional Android developers use Kotlin, and Kotlin Multiplatform adoption has “doubled over past year.” The klibs.io community library registry now lists “3,500+” entries.
Two stable-library releases accompanied the conference: Koog 1.0, JetBrains’ framework for building AI agents on the JVM, and Exposed 1.0, their SQL library for Kotlin. The Navigation 3 library also reached stable status for multiplatform projects.
On the AI tooling front, JetBrains announced co-leadership of the Agent Client Protocol (ACP) alongside Zed — an open standard defining how IDEs and coding agents communicate without vendor lock-in. The Junie coding agent now includes dedicated Android support. JetBrains also noted a benchmark result of an “86.4%” resolution rate for Claude Code with Opus 4.7 on the Kotlin SWE-Bench evaluation.
What We Don’t Know
JetBrains has not announced a final release date for Kotlin 2.4.0. The VS Code extension is in alpha, meaning feature completeness and stability are not guaranteed; JetBrains has explicitly asked users to report what works, what breaks, and what is missing. The productivity study’s methodology relies on telemetry from IntelliJ IDEA Ultimate users, which may not represent the full range of development environments or team structures.