To expand on the earlier answer:
As far as the Kotlin language is concerned, everything is an object: all values inherit from
Any?. (That is, they are either an instance of
null.) This includes numeric literals, as the code in the question shows, along with string literals, character literals, boolean literals, lambdas, numeric variables, &c.
Now, in Kotlin/JVM (if you’re compiling to Java bytecode), the compiler will implement some of those using Java primitives where it can, for efficiency. But that’s completely transparent; the effect is always the same as if full objects were always used.
(If you’re interoperating with Java code, that may need to know. But it’s transparent to Kotlin code.)