Kotlin reached 2.5 million developers worldwide in 2025, defined by three converging vectors: K2 mode becoming the default for IntelliJ IDEA code analysis alongside JetBrains-reported 40%+ compilation time reductions in its IntelliJ monorepo, Compose Multiplatform for iOS reaching stable with 96% of teams reporting no major performance concerns, and an aggressive pivot toward AI-native development with Koog (open-source agent framework) and Mellum (JetBrains code LLM with a Kotlin-fine-tuned variant).

The year brought significant partnerships: JetBrains and Spring formalized Kotlin as first-class (27% of Spring developers have used Kotlin), JetBrains and Azul demonstrated ~30-38% throughput gains on optimized JVMs, and Meta joined the Kotlin Foundation as its first Gold Member. Enterprise adoption accelerated: Google Workspace runs KMP in production in the Google Docs iOS app, JetBrains reports Duolingo ships weekly to 40M+ users with KMP, and JetBrains reports AWS usage in their SDK spanning 300+ services.

However, friction emerged: JetBrains discontinued Fleet IDE, Kotlin dropped to 25th on TIOBE sparking debates about methodology versus domain strength, and K1 deprecation in IntelliJ triggered community reports of legacy Spring Boot 2 project breakage. The replacement—an agentic development environment—signals the company's bet on AI-supervised coding.

Actions for 2026: migrate to K2 compiler now that K1 is deprecated in IntelliJ IDEA 2025.3, upgrade from KAPT to KSP for annotation processing, evaluate Compose Multiplatform now that iOS is stable, plan for Spring Boot 4 GA with Kotlin 2.2 baseline.

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January 27 — Kotlin 2.1.10 bug-fix release for 2.1.0.

February 11 — Ktor 3.1.0 released with Server-Sent Events, CIO engine extensions, and first CIO server for JavaScript.

February 13 — JetBrains announces KMP support deprecation in Fleet, shifting multiplatform tooling focus to IntelliJ IDEA and Android Studio.

February 24 — Ktor 3.1.1 fixed the issue later tracked as CVE-2025-29904 (HTTP Request Smuggling).

March 12 — CVE-2025-29904 published by NVD—medium-severity (CVSS 5.3) HTTP Request Smuggling in JetBrains Ktor before 3.1.1 (updated October 2). Fixed in Ktor 3.1.1+.

March 20 — Kotlin 2.1.20 released with K2 kapt enabled by default, Gradle Isolated Projects compatibility, Kotlin/Wasm debugging/build improvements, and standard library additions like common atomic types and new time-tracking functionality. JetBrains AI Assistant arrives in Android Studio as Beta.

March 27 — Ktor 3.1.2 delivers fixes for Base64 decoding, WebSocket handling, and Kotlin 2.1.20 alignment.

April 2025 — TIOBE Index shows Kotlin falling to #25 (Ruby #24, Swift #26). TIOBE CEO Paul Jansen states Kotlin "seems to have lost traction."

April 2025 — IntelliJ IDEA 2025.1 enables K2 mode by default.

April 2025 — Jetpack Compose April '25 release delivers autofill integration, reduces experimental APIs from 172 to 70.

April 23 — GitHub Copilot code review adds Kotlin support.

May 5 — Ktor 3.1.3 released with performance optimizations.

May 6 — Compose Multiplatform 1.8.0 released. iOS reaches stable with feature parity to Jetpack Compose, VoiceOver support, native-like scrolling, SwiftUI interop, and ~9MB overhead. 96% of teams report no major performance concerns.

May 2025 — JetBrains and Azul unveil strategic collaboration: Kotlin on Azul Zing JVM achieves 24-27% latency reduction and ~30-38% throughput improvement versus OpenJDK ($100/core/year for Zing).

May 13 — Kotlin 2.1.21 adds Xcode 16.3 support.

May 21-23 — KotlinConf 2025 in Copenhagen with 2,150 attendees. Announcements: Koog AI agent framework open-sourced, Mellum (JetBrains code LLM with a Kotlin-fine-tuned variant) unveiled, Compose Hot Reload demonstrated (instantaneous UI changes on devices without restart), official Kotlin LSP for VS Code announced for Alpha. Meta and Block join Kotlin Foundation.

May 2025 — JetBrains announces strategic partnership with Spring—Kotlin formalized as first-class citizen. 27% of Spring developers have used Kotlin.

May 2025 — JetBrains Amper update 0.7.0 continues the build tool's push toward simpler, declarative configuration.

June 12 — Ktor 3.2.0 released with built-in dependency injection, HTMX module, typed configuration DSLs, Gradle version catalog support.

June 23 — Kotlin 2.2.0 released. Key features: stable guard conditions in when-with-subject, context parameters preview, multi-dollar string interpolation, Java 24 bytecode support, Swift Export enabled by default, non-local break/continue.

July 4-29 — Ktor 3.2.1, 3.2.2, 3.2.3 released in quick succession addressing CORS, streaming, and memory leak bugs.

July 7 — kotlinx-datetime 0.7.1 ships with type aliases easing migration to new stdlib kotlin.time.Instant.

July 2025 — Stack Overflow Developer Survey 2025 results: Kotlin at 15th place (10.8% of respondents), 51% wanting to continue using it—among the most "loved" languages.

July 2025 — Android Studio Narwhal Feature Drop introduces Gemini Agent Mode for multi-stage development tasks.

August 8 — kotlinx-rpc 0.9.1 decouples from kotlinx.serialization, enables strict mode by default.

August 14 — Kotlin 2.2.10 bug fix release addressing K2 adoption issues.

August 2025 — Jetpack Compose August '25 release adds Modifier.dropShadow() and Modifier.innerShadow(), enhanced crash debugging.

August 2025 — Next Edit Suggestions launches in Beta—AI recommendations across entire files.

September 10 — Kotlin 2.2.20 released. Kotlin/Wasm graduates to Beta, Swift export available by default, stable KMP library compilation, stack canaries for security, unified shared source set for JS/Wasm.

September 11 — Ktor 3.3.0 released with OpenAPI generation preview and WebRTC client support.

September 2025 — Compose Multiplatform 1.9.0 released. Compose for Web moves to Beta with ARIA accessibility, browser history management, WebElementView for HTML embedding, Frame Rate Configuration for ProMotion displays.

October 23 — Kotlin 2.2.21 released with Xcode 26 support.

October 2025 — Android Studio Otter 2025.2.1 reaches stable with Gemini AI integration.

November 2025 — Meta joins Kotlin Foundation as first Gold Member; Block joins at Silver level.

November 18 — Kotlin 2.3.0 RC published with unused return value checker and explicit backing field syntax.

November 20 — Spring Boot 4.0 reaches GA with Kotlin 2.2 baseline and JSpecify integration. Kotlin support details follow in December.

November 2025 — JetBrains and Inflearn offer KotlinConf 2025 session recordings free online with multilingual subtitles, covering 76 talks.

December 8 — IntelliJ IDEA 2025.3 releases as "Unified IDE"—Community and Ultimate editions merged, more features free.

December 8 — JetBrains announces Fleet discontinuation effective December 22. Admits Fleet "did not create enough value." Pivots to a new agentic development environment.

December 2025 — JetBrains deprecates K1 compiler in IntelliJ IDEA: ~98% of projects using K2, ~1% forcing K1 mode.

December 16 — Kotlin 2.3.0 released. Key features: experimental unused return value checker, explicit backing fields syntax, Java 25 bytecode support, up to 40% faster Kotlin/Native release builds, new inlining optimization pass, smaller binary sizes, Kotlin enums export as true Swift enums with variadic function support, Wasm exception handling default, Beta C/Objective-C library import, return statements in expression-bodied functions default, improved UUID generation, stable Time Clock API, Gradle 9.0 compatibility, Android Compose compiler meaningful stack traces in release builds.

December 2025 — In the 2025.3 line, AI Assistant expands BYOK options and agent support; the supported model roster includes Claude 4 Sonnet, Gemini 3 Pro, and Grok 4.

December 2025 — Android Studio Otter 2 Feature Drop adds Agent Mode with Android Knowledge Base and Gemini 3 Pro Preview.

K2 performance gains are now documented across IDE and build workflows. JetBrains reports 40%+ compile time reductions in its IntelliJ monorepo, while K2 benchmarks show a ~1.94x faster Anki-Android clean build and 376% faster incremental analysis, with IDE code analysis and completion seeing ~39% and ~26% improvements in IntelliJ IDEA 2025.3. K2-Enabled features on the roadmap include Rich Errors, when guard conditions, and multi-dollar interpolation for template-heavy code.

Performance wins show up beyond the compiler: Kotlin on Azul Zing reports ~30-38% throughput gains and ~24-27% latency reductions, Gradle 9.0 improves Kotlin DSL feedback by 2.5x, KSP can be up to ~2x faster than KAPT, and Kotlin/Native release builds are up to 40% faster in 2.3.0. Tooling continues to move off KAPT toward KSP and Kotlin 2.x-aware rules.

Kotlin sits at 2.5 million developers worldwide and ranks 15th in the Stack Overflow 2025 survey (10.8%), with 51% wanting to continue using it. RedMonk places Kotlin at 14th, while TIOBE puts it at #25; JetBrains' 2025 developer ecosystem survey (24,534 developers across 194 countries) lists Kotlin as 6th in "want to adopt next" and 8% of backend developers' primary language. Kotlin usage in Spring is also measurable, with 27% of Spring developers reporting they have used it, and the Kotlin Slack community has crossed 100K users.

Adoption is increasingly enterprise-visible: Google Workspace runs KMP in production for the Google Docs iOS app, Duolingo ships weekly to 40M+ users with KMP features, and AWS reports its Kotlin SDK spans 300+ services across 8 platforms. JetBrains' KotlinConf stage highlights add further evidence of scale, citing Kotlin migrations or production deployments at companies like Uber, N26, ING, McDonald's, Netflix, Mercedes-Benz.io, Roblox, and others.

When: IntelliJ IDEA 2025.3 deprecated K1; removal timing is not yet specified.

Context: ~98% of projects already use K2, with ~1% still forcing the old mode. Legacy projects on Kotlin 1.5/1.6 (Spring Boot 2 era) may face IDE issues, with community reports of breakage.

Action: Upgrade to Kotlin 2.x and run ./gradlew build with K2 to identify compatibility issues. Migrate Spring Boot 2 projects to Spring Boot 3+ as prerequisite.

When: Now. KAPT may enter formal deprecation in 2026.

Context: KSP (Kotlin Symbol Processing) is typically faster than KAPT. Major libraries (Room, Moshi, Dagger) fully support KSP. KAPT is slow and incompatible with K2's full performance benefits.

Action: Audit build.gradle.kts for KAPT usage. Migrate annotation processors to KSP equivalents. Use ksp() instead of kapt() in dependency declarations.

When: Now. iOS stable since May 2025, Web Beta since September 2025.

Context: 96% of teams report no major performance concerns on iOS. VoiceOver support, native-like scrolling, and SwiftUI interop remove previous blockers. ~9MB overhead per app.

Action: Evaluate Compose Multiplatform for new cross-platform projects. Existing KMP projects: migrate shared UI from platform-specific to Compose. Web targets: evaluate Beta for internal tools.

When: Expected June-July 2026.

Context: Likely features: name-based destructuring stabilization, enhanced nullability checks, Context Parameters graduation to stable (enabling cleaner DI patterns), stable K2 compiler plugin API. Release cadence: six months for language releases, three months for tooling releases.

Action: Track Kotlin 2.3.20 (March-April 2026) for early feature previews. Enable experimental features in test projects to provide feedback.

When: Stable expected late 2026.

Context: Kotlin/Wasm graduated to Beta in September 2025. Exception handling enabled by default in 2.3.0. Unified shared source set for JS/Wasm simplifies multiplatform web targeting.

Action: Evaluate for compute-intensive web applications where TypeScript performance is insufficient. Test with Compose for Web for full-stack Kotlin.

When: Now. Spring Boot 4.0 GA with Kotlin 2.2 baseline.

Context: JetBrains-Spring partnership formalized Kotlin as first-class. Spring Boot 4 eliminates platform types through JSpecify integration, adds native kotlinx.serialization starter, with a Kotlin support deep dive. 27% of Spring developers have used Kotlin.

Action: Upgrade Spring Boot 3.x projects to 4.0. Enable kotlinx.serialization starter for JSON handling. Leverage JSpecify null-safety annotations.

When: Broader preview expected 2026.

Context: JetBrains discontinued Fleet and is building a new agentic development environment where developers supervise AI agents. Success depends on whether developers embrace supervisory AI workflows.

Action: Monitor agentic IDE preview releases. Evaluate against existing IDE + AI Assistant workflow. Consider for greenfield projects where AI-first development is acceptable.

When: Ongoing. Monitor Ktor releases.

Context: CVE-2025-29904 (HTTP Request Smuggling) and CVE-2025-12543 (Undertow Host Header Bypass) demonstrated attack surface in Kotlin web frameworks. Ktor 3.x received rapid patches throughout 2025.

Action: Pin Ktor to 3.3.0+ for new projects. Audit existing deployments for versions <3.1.1. Enable automatic dependency updates via Dependabot or Renovate.

When: Stable expected 2026. Beta since Kotlin 2.2.0.

Context: Swift Export enables producing Apple frameworks from Kotlin. Kotlin 2.3.0 exports enums as true Swift enums with variadic function support. Up to 40% faster release builds.

Action: Evaluate for KMP projects targeting iOS. Replace manual Objective-C interop with Swift Export where possible. Test enum and variadic function exports.

When: May 20-22, 2026 in Munich, Germany.

Context: First "Golden Kodee Community Awards" ceremony. February 2026 marks 10 years since Kotlin 1.0 (February 2016)—expect retrospective celebrations and long-term vision announcements.

Action: Track CFP announcements for submission deadlines. Plan attendance for enterprise roadmap alignment.

When: Ongoing through 2026.

Context: Java: Project Valhalla's value types may preview in 2026, potentially overlapping with Kotlin value classes. Java has caught up with records, pattern matching, and Project Loom virtual threads. Swift: SwiftWasm targets WebAssembly, potentially competing with Kotlin/Wasm. An opinion piece argued Kotlin needs a "big new killer feature" to maintain its edge.

Action: Monitor Java 23+ for Valhalla preview. Differentiate with KMP, DSL capabilities, and AI tooling. Evaluate Kotlin/Wasm against SwiftWasm for web targets.

When: Various dates through 2026.

Context: Multiple deprecations affecting legacy projects:

Action: Audit projects for deprecated features. Migrate kotlin-android-extensions to View Binding or Compose. Upgrade minimum deployment targets for Apple platforms.

When: Ongoing. Koog, Mellum, Junie, and the AI Assistant 2025.3 line are available now.

Context: Mellum is a JetBrains code LLM with a Kotlin-fine-tuned variant open-sourced in 2025, leveraging K2's semantic understanding for "compiler-verified" AI with reduced hallucinations. Koog enables building AI agents in type-safe Kotlin with Model Context Protocol (MCP) support. Junie demonstrated at KotlinConf as AI pair programmer handling multi-module tasks. JetBrains cites Kotlin as ~30% less code and ~25% fewer bugs than Java, making it more "AI-friendly." Stack Overflow 2025 shows 46% of developers distrust AI accuracy (only 3% highly trust)—adoption requires validation. Agent Client Protocol (ACP) developed with Zed aims to standardize AI agent integration across IDEs.

Action: Evaluate Mellum/AI Assistant for Kotlin-specific code completion. Consider Koog for AI agent development if currently using Python frameworks. Implement code review for AI-generated code.

When: Expanding in 2026.

Context: JetBrains partnered with Xebia Academy for intensive Kotlin Upskill Program in 2025. Trend likely to expand with more official training pathways for enterprises.

Action: Evaluate official training for teams adopting Kotlin. Track new certification offerings.

When: Ongoing. Monitor dependencies continuously.

Context: In September 2025, one npm supply-chain campaign targeted 18 popular packages with billions of weekly downloads, with payloads aimed at crypto wallets. Separately, the self-propagating "Shai-Hulud" worm compromised hundreds of packages and harvested credentials; Shai-Hulud 2.0 escalated execution to the preinstall phase. These incidents primarily impacted JavaScript ecosystems but could affect Kotlin/JS and KMP projects with JS targets. No Kotlin-specific incidents reported, but the ecosystem relies on Gradle and Maven Central. Qodana used by JetBrains on Kotlin codebase for quality assurance.

Action: Enable Gradle dependency checksum verification. Configure OWASP Dependency Check or GitHub Dependabot. Audit build.gradle.kts dependencies in multiplatform projects, especially JS targets.