[jacurtis]

First class is always full. If you have status with the airlines you can get free upgrades to first class now. So they start releasing upgrades like 3 days ahead of time for the best statusholders. Then 2 days before they release upgrades for the middle tiers, and same-day or day before is the lower tiers. They basically try to shift everyone up a tier in the flight and the extra coach seats that those people left behind will get filled with the basic-economy fliers, which is why they don't let them reserve seats: they just use them to fill in the gaps on the flight.

You are more likely to have an empty seat next to you in the back of the plane than in the first class.

[jethro_tell]

Yes, its always full bit it's not always sold. An upgrade is the airline turning an unsold seat into a potential future sold seat or customer good will.

But they don't get full price for it in any way. They'll take money to seat kids there if you wanna pay.