The other program is a day-of-departure upgrade program. Under this program, a customer is offered an upgrade to F for a nominal fee only if there are more F seats than there are elites awaiting an upgrade
I fear this changed recently? Sunday evening I flew IAH>MSY on an H ticket, 16 front seats in the 738.
I'm Plat - checked in Saturday pm and offered F buy-up for $2 - yes, two dollars

Declined. Three hours before departure PDA showed 6 First booked and 1 upgrade; I was high on the upgrade list. Did eventually clear along with 9 other pax.
Has the system been tweaked? I favor CO over WN as they usually show me a better time. If they're starting after chump-change for the privelege, they'll have lost the edge.