How Major Metros Run on KMP

Every time you tap through a subway gate in New York City, you’re using Kotlin Multiplatform! In this episode, we sit down with Paweł Kwieciński from Masabi to explore how they brought a decade-old Java codebase to KMP, powering ticket validation across mobile apps, embedded devices, and backend systems for public transit agencies worldwide. Resources: Masabi J2ObjC (Java to Objective-C translator) Google Workspace Migration to Kotlin Large Scale Changes with AI – Uber | Ty Smith KotlinX DateTime Ktor (Client & Server) Burst library (archived) Java ME (Micro Edition) Mbed TLS SQLDelight Compose Multiplatform JetBrains AI Assistant & Junie Hosts: Sebastian Aigner – Website | Bluesky Márton Braun – Website | Bluesky Guest: Paweł Kwieciński Timeline: (0:00) Introduction (1:12) What is Masabi? (3:03) How does Kotlin fit into this? (6:30) System architecture overview (8:33) Embedded SDK and mobile apps (10:33) Ticket inspectors and validators (13:22) Offline operation (16:29) The KMP decision (24:42) Evaluating alternatives (27:21) Planning the migration (33:28) First lines of Kotlin (43:45) Translating Java to Kotlin (53:22) AI-assisted code translation (56:39) Early AI era challenges (1:05:01) Testing challenges (1:08:22) KMP dependencies (1:11:34) Domain-specific dependencies (1:16:55) Java ME and C interop (1:23:22) Backend-client sharing (1:26:59) Current status (1:31:48) Future plans: CMP (1:36:26) Wrap-up

You can listen to How Major Metros Run on KMP online on Radio and Podcast. Open the player on this page to stream the available audio.

How Major Metros Run on KMP is an episode from Talking Kotlin by Talking Kotlin.

This episode is 01:39:25 long.

This episode was published on Mar 5, 2026.

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