Jetbrains has been using Kotlin in house since at least 2011. At my company we started using Kotlin when it turned 1.0 in Feb 2016. It's been a huge success wit

Jetbrains has been using Kotlin in house since at least 2011. At my company we started using Kotlin when it turned 1.0 in Feb 2016. It's been a huge success with programmer productivity and happiness. Currently have 18000+ lines of Kotlin in production. Whenever given the chance we refactor large Java classes that are 1500ish lines to 300ish lines of Kotlin. Compared with switching from Obj-C to Swift, the transition was relatively seamless. No bridging header for interop with Java. Also Android Studio/IntelliJ has very mature language support for Kotlin that should keep most IDE driven developers happy.