while Kotlin has only a single

Int

type conceptually, the compiler will represent it with a boxed Integer or primitive int as appropriate, automatically

this is all covered in the documentation, https://kotlinlang.org/docs/basic-types.html#numbers-representation-on-the-jvm

a

<http://kotlin.Int|kotlin.Int>

is never a mutable box. on JVM, it is represented by either a primitive

int

wherever possible, or an immutable boxed

java.lang.Integer

where not

you should consider

Int

to be like other value types: they have no identity, so instances (and whether they're the same or not) aren't even part of the language model