Talking Kotlin

Sebastian and Márton host a special, audio-only episode where they discuss everything that’s new and noteworthy in the Kotlin 2.3 release. They touch on new language features like the unused return value checker and explicit backing fields, previously added features that became stable in this release, new APIs for time and UUID handling in the standard library, and improvements across all Kotlin platforms — from Native to Wasm and JS.
Resources:
What’s new in Kotlin 2.3
KotlinConf
Golden Kodee Community Awards
Hosts:
Sebastian Aigner – Website | Bluesky
Márton Braun – Website | Bluesky
Timeline:
(0:00) Intro
(1:13) Nested type aliases (stable)
(1:46) Data-flow based exhaustiveness checks (stable)
(3:28) Return statements in expression bodies
(4:19) Unused return value checker (experimental)
(12:57) Explicit backing fields (experimental)
(18:51) Context-sensitive resolution (experimental)
(20:11) Clock and Instant in the standard library (stable)
(21:52) UUID v7 support and better parsing
(26:14) Java 25 bytecode
(26:36) Faster Native release builds
(27:45) Swift Export: enums and varargs
(29:08) C and Objective-C library import (beta)
(30:49) Apple target support changes
(32:15) Fully qualified names in Kotlin/Wasm
(34:10) New exception handling for wasmWasi
(35:32) Suspend function export to JS
(37:51) LongArray export to JS
(38:40) Unified companion object access in JS
(41:05) @JsStatic inside interfaces
(41:43) Default exports in JS
(43:45) Compose stacktraces for minified Android apps
(45:23) Breaking changes 🐜
(46:14) Documentation updates
(47:24) KotlinConf, Golden Kodees Awards
(48:11) Wrap-up

Sebastian and Márton talk to Vadim Briliantov, the Technical Lead for Koog: an agentic framework built by JetBrains. We learn about what AI agents are, and why building them in Kotlin with Koog is a great choice. We also discuss all the different ways AI agents can connect to other systems and your existing code, and look at advanced features for agents like custom strategies, model switching, and history compression.
Resources:
JetBrains/koog on GitHub
Koog Documentation
Hosts:
Sebastian Aigner – Website | Bluesky
Márton Braun – Website | Bluesky
Guest:
Vadim Briliantov – LinkedIn | Medium | GitHub | Bluesky | Twitter/X
Timeline:
(0:00) Intro
(1:11) Vadim’s history at JetBrains
(4:21) What’s an AI Agent?
(5:47) Koog!
(7:12) Applications for agents
(12:43) Koog’s building blocks
(15:05) Strategies, feedback loops
(23:55) The Kotlin DSL
(26:12) Persistent state
(29:48) Subgraphs
(32:33) Tools
(39:52) MCP support (and A2A)
(44:01) Entry point and type safety
(49:39) Spring and Ktor support
(51:27) LLM Providers
(53:30) Model switching
(56:02) History and memory
(59:22) Enterprise-ready
(1:02:12) History compression
(1:11:47) Markdown?!
(1:14:37) What’s next?
(1:18:22) Going open-source
(1:20:32) Conclusion

Sebastian and Márton chat with Marcin Moskała about coroutines.
Resources:
Coroutines Mastery course
Coroutines | Kotlin Documentation
kotlinx.coroutines
Taming Asynchronous Beasts | Marcin Moskała
Coroutine Debugging in IntelliJ IDEA | Alexey Merkulov
Lifecycles, Coroutines and Scopes | Alejandro Serrano Mena
Collect Like a Pro | Manuel Vivo
Untangling Coroutine Testing | Márton Braun
JetBrains/lincheck – Concurrent testing framework
#talking-kotlin on Kotlin Slack
Hosts:
Sebastian Aigner – Website | Bluesky
Márton Braun – Website | Bluesky
Guest:
Marcin Moskała – kt.academy
Timeline:
(0:00) Introduction
(1:18) Branding discussion
(3:23) Handling preconceptions
(4:54) What are coroutines?
(7:17) Lightweight threads?
(11:07) Where coroutines live
(13:27) Sequence Builder Example
(17:37) The design of coroutines
(20:52) What Makes Coroutines special vs other languages?
(26:56) Coroutines vs Loom
(34:55) Easy to start, hard to master
(41:07) Common mistakes
(49:33) Flows
(58:52) Thinking about Flows
(1:02:41) Derailing the conversation
(1:03:55) Flows for single values
(1:12:27) Structured concurrency
(1:18:53) The 4 advantages
(1:24:40) Seb tries web dev / The web is broken?!
(1:31:15) collectAsStateWithLifecycle
(1:32:00) Gardening break
(1:36:23) Scopes and contexts
(1:43:22) Testing coroutines
(1:50:29) Lincheck
(1:51:32) Turbine
(1:55:05) Coroutines Mastery course
(2:01:43) Wrap-up

Sebastian and Alex chat about the kotlinx.rpc project, in a special episode recorded in the Munich JetBrains office. They explore all the different components of the library, how you can use it to define RPC services and clients, integrate with Ktor and existing gRPC definitions, and more. While the library is still experimental, it’s already feature-packed, and it has ambitious plans for the future!
kotlinx-rpc on GitHub
#kotlinx-rpc on Slack
kotlinx.serialization on GitHub 
gRPC

Host: Sebastian Aigner
Website
Bluesky

Guest: Alex Sysoev
LinkedIn
GitHub

Sebastian and Márton are joined by Denis Borisevich from RIEDEL Communications, and learn about how Kotlin is used behind-the-scenes to power media, sports, and entertainment broadcasts watched by millions around the globe. Tune in for an exciting story about how Kotlin, Ktor, and Arrow are being used in production for a use case where robust software is mission-critical.
Resources:
Riedel Communications
TornadoFX
Unsigned integer types
Arrow
Ktor
Eurovision
Hosts:
Sebastian Aigner – Website | Bluesky
Márton Braun – Website | Bluesky
Guest:
Denis Borisevich – LinkedIn
Timeline:
(0:00) Introductions
(2:42) Events powered by Riedel
(3:50) The Kotlin part
(6:44) Routing video signals
(9:12) Error handling in milliseconds
(10:31) The Kotlin part, continued
(13:29) TornadoFX!
(19:19) On introducing Compose
(23:30) Java to Kotlin migration
(26:30) Learning Kotlin after C++
(28:44) Unsigned ints in Kotlin
(32:09) Arrow!
(33:00) Server-side Kotlin
(36:25) Functional programming
(42:10) Why Kotlin over others?
(45:55) Kotlin/Java interop
(47:12) A 2-week long test suite
(51:35) Confidence in Kotlin
(53:05) Future plans
(56:00) Wrap-up