Note that this is from 2009. Although the main details have not changed, the int type is more commonly 64 bits now (since 64 bit architectures are much more common)
package main
import "fmt"
import "reflect"
func main() {
i := 3
z := reflect.ValueOf(i)
fmt.Printf("%s\n", z.Kind())
}
// $./test
// int
// $
There is also a set of predeclared numeric types with implementation-specific sizes:
uint either 32 or 64 bits
int same size as uint
uintptr an unsigned integer large enough to store the uninterpreted bits of a pointer value