All depends on availability. I have a trip to Tokyo this month on AA, and another to London next month, and they're both upgraded already with systemwides. I check availability before booking my flights to make sure they will clear (looking for C class availability). In the case of my London flight, there was no advance availaibility on the nonstop LAX-LHR, so I'm going via JFK to secure the upgrades up front. I hate waiting for upgrades to clear at the gate. The last time I did that on international was on UA SFO-SYD a couple years ago, which fortunately did clear, but now I book depending on where I can get the upgrade right now.