[pron]

Kotlin announced that until the upcoming 1.0 release there will be breaking changes, but not after. Binary compatibility will not be 100% guaranteed, but it's a high priority.

[justthistime_]

So there will be basically no change to the status quo?

Looks like Kotlin will join Ceylon in terms of promising things and then failing to ship them. Post-1.0 Ceylon is still breaking compatibility.