Now that United Airlines converted to Shares and the old upgrade and award fare buckets no longer exist, I thought it might be helpful to summarize the new ones as shown in the below chart. The new alphabet soup has gotten a touch more complex depending on your elite status, so I’ve broken out the correct buckets by level.
The first “Upgrade” category covers burning your miles (+co-pay) or using a confirmable instrument (RPU/GPU), but also includes Complimentary Premier Upgrades where applicable from coach to the next cabin. The “Y/B/M Upgrade” section refers to the instant-upgrade program when buying full-fare coach tickets (or M-fares for 1K and Global Services members) in CPU markets (most domestic markets plus a few intra-Asia).
This is the new system in theory at the moment, as I have yet to attempt to book an award in one of the two-character buckets ending with –N. My reservation to Australia that was converted from Apollo shows my upgrade to business as simply being in the R-cabin, though we as customers might only see the first character online after a reservation is booked.
To view a flight’s allocation of inventory, simply click into the “Fare classes” link that appears on the right-hand side of a flight search when you go to make a reservation.