Definitely not available with someone else's miles. You have no option to identify 'which miles' are to be used. To illustrate: I wanted to auto upgrade two pax on the same PNR. This could not be done, as there were not enough miles in MY account to upgrade both of us. I could not specify that each of us had to be upgraded with miles out of our own accounts. I contacted the call centre and the agent confirmed this!

I wonder how auto upgrade works when there are multiple auto upgrade requests for one available upgrade? First come first serve? Status? Or original booking class (like the op-ups)?