Kotlin in 2025: What's New? A Practical Overview for Developers

Kotlin in 2025: What's New? A Practical Overview

2025 has become a landmark year for the Kotlin ecosystem. The language, which started as an "improved Java" for Android, has finally transformed into a universal tool covering server-side development, web frontend, native applications, and even Data Science. In this article, we will break down the key changes that have occurred in Kotlin by 2025 and demonstrate them with real code examples.

1. Kotlin Multiplatform (KMP) — Stability and Maturity

The main event of recent years is Kotlin Multiplatform exiting beta and achieving stable product status. If KMP was previously perceived as an experimental technology, in 2025 it is the primary way to write cross-platform business logic.

What changed:

• Full support for kotlinx.serialization for all platforms "out of the box".
• Improved integration with Swift and Objective-C via the new @ObjCName.
• An official Gradle plugin has been introduced that automates module configuration.

Example: Shared code for Android and iOS

// commonMainimport kotlinx.serialization.Serializableimport kotlinx.serialization.json.Json

@Serializabledata class User(val name: String, val age: Int)

class UserRepository {    private val json = Json { ignoreUnknownKeys = true }        fun parseUser(data: String): User {        return json.decodeFromString(data)    }        fun greet(user: User): String {        return "Hello, ${user.name}! You are ${user.age}."    }}

Now this code works on Android (via Kotlin/JVM) and iOS (via Kotlin/Native) without any changes. In 2025, you don't need to add additional experimental annotations for this — everything is stable.

2. New Package Manager and Improved DSL

In 2025, the JetBrains team introduced an updated version of Gradle (8.10+) with a native DSL for Kotlin. The main innovation is a declarative description of dependencies with automatic version conflict resolution.

Example of the new build.gradle.kts syntax:

plugins {    kotlin("multiplatform") version "2.1.0"    kotlin("plugin.serialization") version "2.1.0"}

kotlin {    jvm()    iosArm64()    iosSimulatorArm64()        sourceSets {        commonMain.dependencies {            implementation("org.jetbrains.kotlinx:kotlinx-coroutines-core:1.9.0")            implementation("org.jetbrains.kotlinx:kotlinx-serialization-json:1.7.0")        }        jvmMain.dependencies {            implementation("io.ktor:ktor-server-netty:3.0.0")        }    }}

// New block for automatic version updatesdependencyLocking {    lockAllConfigurations()    lockMode = LockMode.STRICT}

Built-in support for Version Catalogs (libs.versions.toml) has also been added, which is now generated automatically on the first run.

3. Compiler Performance and New Language Features

Kotlin 2.1 and 2.2 brought significant improvements in compilation speed. According to JetBrains tests, incremental builds are 30-40% faster compared to Kotlin 1.9. This was achieved thanks to the new backend based on IR (Intermediate Representation), which is now used by default for all platforms.

Key language features of 2025:

• Guard conditions in when — you can now add additional checks directly in the condition.
• Context receivers — a stable feature for dependency injection without frameworks.
• Extended inline classes — support for multiple parameters and methods.

Example: Guard conditions

fun process(value: An