This question is based off of an experience I had on AS where I was allowed to buy up to F at the gate relatively cheaply. It rebooked into U class (so no extra miles) but it was still a good experience for domestic F. Last November I flew SAN-LAX-HNL-SFO-SAN on PMUA. Once in a while I would log in and review the itinerary for special offers. There were a couple of times where opportunities to buy up to F were available. What caught my eyes was that SFO-SAN was $55 to upgrade well before day of departure. I didn't feel it was worthwhile to do as I was coming off a four-hour flight in Y and that segment is short (about 75-ish minutes in the air). This November I have SAN-DEN-SAN booked for an upcoming trip, and to bump to F costs $428 each way. Obviously I'm not going to pay that - but now I'm wondering if there are good windows of opportunity to pay a little more and less than the prevailing rate to get a better flight experience. Has anyone done this before? If so, when should I start looking for a better opportunity to do so? Or is post-merger UA Revenue Management smarter than I am and I should just drop the idea entirely or wait to get to the gate?