KotlinConf’26: Kotlin Toolchain, Koog Stable, What to Do Now

KotlinConf’26 is running in Munich this week (May 20–22), and the keynote wasn’t just a language version update. JetBrains shipped a unified Kotlin Toolchain to replace the Gradle configuration maze, declared Koog production-stable for AI agents across the JVM stack, locked in context parameters for Kotlin 2.4, and handed KMP a Duolingo-sized stamp of approval. Here’s what each announcement means for your codebase — and what to actually do about it.

Kotlin Toolchain: One CLI to Replace Gradle

This is the biggest quality-of-life change in Kotlin’s build story in a decade. The Kotlin Toolchain is a single CLI entry point covering create, build, run, test, format, doc generation, and agent integration. Amper — JetBrains’ YAML-based build system — is the engine inside it, and it’s available now for JVM and multiplatform projects.

The practical wins: Amper auto-provisions JDK 21, supports Ktor, Spring, Android, and KMP out of the box, and replaces Gradle’s notoriously verbose configuration with a clean module.yaml file. Gradle will stay around for projects that need its plugin ecosystem, but for new Kotlin projects, the Toolchain is the right default now.

JetBrains plans to expand it with LSP integrations, AI skills, and native dependency provisioning. For now, start with kotlin toolchain create — and a build config that doesn’t require a PhD.

Koog Is Production-Stable — and It’s a Real LangChain Alternative

Koog, JetBrains’ AI agent framework for the JVM, is now production-stable with full semantic versioning and a no-breaking-changes guarantee on stable APIs. It runs across JVM, Android, iOS, JS, and WasmJS — meaning an agent you write in Kotlin can deploy to a Spring Boot backend, an Android app, and a browser without rewriting the core logic.

The features that matter most for backend teams: agent persistence (agents recover state after a restart), built-in fault-tolerance with retries, and a pluggable HTTP factory that works with Ktor, OkHttp, or Java’s built-in HTTP client. For Spring users, the integration is minimal — Koog’s PromptExecutor is auto-configured from your existing Spring AI ChatModel. For Ktor users, it’s one install(Koog) call with YAML configuration.

Java teams aren’t left out. Koog now has a fully idiomatic Java API using fluent builders and a xxxBlocking pattern, with fixed reentrant call issues that previously caused deadlocks in Kotlin↔Java call chains.

This puts Koog in direct competition with LangChain4j. Koog’s advantages: Kotlin-coroutines-native, type-safe workflow DSLs, and now ACP-connected for IDE integration. LangChain4j has a broader plugin ecosystem, but for teams already on Kotlin, Koog is the better pick. The Spring AI integration takes under 30 minutes to set up.

Context Parameters Are Stable: Remove That Compiler Flag

Context parameters — Kotlin’s mechanism for passing implicit dependencies cleanly through call chains — graduate to stable in Kotlin 2.4. The immediate action item: remove -Xcontext-parameters from your freeCompilerArgs. You no longer need it.

More importantly, context receivers — the older experimental feature from Kotlin 1.6.20 — are heading toward deprecation. Refactor them to context parameters now. Context arguments and callable references for context parameters are still in progress, so hold off on those.

KMP Has Already Crossed the Chasm

The keynote numbers are hard to argue with. Top apps doubled their KMP usage in a year. Duolingo ships to 40M+ weekly users on KMP. PayPal, Booking.com, Netflix Studio, and Google Docs iOS are in production. Adoption sits at 23%, up from 7% two years ago.

Navigation 3 — the Compose-first navigation library — is now stable for Android, iOS, desktop, and web via Compose Multiplatform 1.10. If your team is still on the “wait and see” timeline with KMP, the wait is over.

Agent Client Protocol: Build Agents That Live in IDEs

JetBrains and Zed co-lead the Agent Client Protocol (ACP) — an open standard that lets any AI coding agent work in any supporting editor, similar to how LSP normalized language tooling. Koog agents are ACP-compatible, meaning agents you build with Koog can be installed directly into JetBrains IDEs and Zed via the ACP Agent Registry (live since January 2026).

For most teams this is a watch-this-space item. For teams building custom internal agents, it’s worth implementing now for free IDE distribution.

What to Actually Do This Week

• Run kotlin toolchain create on your next new project — skip the Gradle boilerplate
• Add Koog to an existing Spring Boot or Ktor service — the Spring AI integration wires in 30 minutes
• Remove -Xcontext-parameters from your build config and start migrating context receivers before they’re deprecated
• Read the Kotlin 2.4 RC release notes — stable lands in June or July, and there are more changes to prepare for
• Check the full KotlinConf’26 keynote post for the complete announcement details