Kotlin in 2025: What's New and Why It Matters

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Kotlin in 2025: Overview of Major Changes and New Features

The year 2025 has been a landmark year for the Kotlin programming language. Developers from JetBrains and the community have introduced a number of key updates that make Kotlin even more attractive for backend development, mobile applications, as well as for data science and web development. In this article, we will break down the main innovations that were released or became stable in 2025, and see how they are changing the ecosystem.

1. Stable K2 Compiler: Performance and Compatibility

The main event of the year is the full transition to the K2 compiler, which has moved from experimental status to stable. K2, based on a new architecture (Frontend on Kotlin/Native), provides a significant performance boost and improved IDE support.

Compilation speed: K2 shows a 1.5–2 times speedup compared to the previous compiler.
Smart suggestions: Thanks to the new analyzer, IntelliJ IDEA and Android Studio now highlight errors and suggest refactoring more accurately.
Backward compatibility: All existing Kotlin 1.x code is fully compatible with K2.

Example of using new syntax made possible by improved type inference:

// Kotlin 2025 — improved type inferenceval numbers = listOf(1, 2, 3)val doubled = numbers.map { it * 2 } // K2 automatically infers type List<Int>println(doubled) // [2, 4, 6]

// New syntax for sealed classes (now possible without declaration in the same file)sealed interface Result {    data class Success(val data: String) : Result    data class Error(val message: String) : Result}

2. Kotlin Multiplatform (KMP) 2.0: Unified Codebase for All Platforms

In 2025, the second major version of Kotlin Multiplatform was released. Now KMP is not just a technology for Android/iOS, but also a full-fledged solution for backend (JVM, Native, WASM) and web (Kotlin/JS).

Key improvements:

Stable Kotlin/Wasm: WebAssembly support has become stable. This allows running Kotlin code in the browser with near-native performance.
Improved Gradle integration: The new configuration system (Kotlin DSL 2.0) simplifies setting up multiplatform projects.
Shared libraries: It is now possible to write common code for UI (Compose Multiplatform) and business logic without duplication.

// Example of a common KMP module for networkingimport io.ktor.client.*import io.ktor.client.request.*import io.ktor.client.statement.*

// This code works on Android, iOS, JVM, and JSsuspend fun fetchData(url: String): String {    val client = HttpClient()    val response: HttpResponse = client.get(url)    return response.bodyAsText()}

3. New Language Features: Context Functions and Improved Coroutines

Kotlin continues to evolve its paradigm. In 2025, several experimental but already testable features were added:

3.1 Context Functions (Context Parameters)

This feature allows passing implicit parameters (context) to functions without using this or global variables. This simplifies writing tests and working with DI.

// Declaring a context functioncontext(Logger)fun logMessage(message: String) {    log(message) // log is taken from the context}

class Logger {    fun log(msg: String) = println("LOG: $msg")}

fun main() {    val logger = Logger()    with(logger) {        logMessage("Hello, 2025!") // Works thanks to the context    }}