Kotlin 1.3.40: https://youtrack.jetbrains.com/issues/KT?q=%231.3.40
I don’t know anything about 1.4. I guess the Kotlin team will publish a couple of blog posts about the features in it before it will be released, but I don’t remember seeing anything.
The answer I remember seeing to the question “when will it be released” has always been “when it’s ready” but v1.4 is probably some time away, since we don’t have any concrete information about it. Also if they keep up the speed of releases I guess 1.4 will be released at the end of this year. v1.2 was released in November and v1.3 a year later in October. So I guess 1.4 will be release around that time as well.
The only feature I can think of that will be part of v1.4 (probably) is the new type inference backend. It’s already part of kotlin as an experimental optional system but I guess they will switch to it when v1.4 is released