Global Entry interview on arrival for me was essentially confirming who I was, asking what trips I currently had booked to the US and their purpose, and then explaining how the system worked. And I have to say, the system is pretty good - on a recent arrival into JFK the terminal took my photo and then instantly issued me with a chit to take to the desk. I didn’t have to scan my passport, or show it to anybody. Best £140ish I’ve ever spent