Alaska Airlines will only sell upgrades for cash 24 hours before departure, if there's confirmed upgrade space. This is great news, especially for elite members. It means your Alaska Upgrade to First Class will not be sold to someone else paying cash. This is fair. Alaska also doesn't have last seat availability for cash upgrade. You must actually have U-class upgrade space to be able to upgrade for cash. Not just a sale seat. You can't pay cash instantly to upgrade to a U-class seat as long as there are seats available.