Yeah you&#x27;ve got full interop with Java. There is some overhead in terms of executable size, but not significant. As for commercial apps written in Kotlin, I have no way of knowing, but there&#x27;s a lot of open-source projects. It wasn&#x27;t long ago that Kotlin reached 1.0, and prior to that I would myself err on the safe side not recommending it for production yet. It&#x27;s been improving very fast though.