Reference semantics are part of the type.

So "var i: int" is value, "var i: ref int" is a heap allocated reference that's deterministically managed like a borrow checked smart pointer, eliding reference counting if possible.

You can turn off GC or use a different GC, but some of the stdlib uses them, so you'd need to avoid those or write/use alternatives.

Let me say though, the GC is realtime capable and not stop the world. It's not like Java, it's not far off Rust without the hassle.