Who knows. But to add to the discussion, I got a ticket on the PFD sale this year, and it was a "K" class fare - definitely falls into the "hot deals" category. So here's what we seem to be able to deduce from the website, jackal's T fare, my PFD special, and some seatcounter.com sleuthing on my relaxing post-Iditarod afternoon:

F - purchased 1st class fare

U - first class upgrade seat (mileage/complimentary status upgrades/coupons)

Y (sometimes called YAS) - Full Flex (automatically upgradeable for MVP's and MVPG's anytime U is available)

S, B > M > H - Value (automatically upgradeable for MVPG's anytime U is available)

Q > L > V > G - Bargain

T - hot deals (jackal's fare)

K - hot deals (my PFD fare)

Several disclaimers/points to bear in mind:

• Above ordered fare basis codes are essentially guesses based on seatcounter.com and alaskair.com available information
• Delineation between Bargain and Hot Deals codes may be inaccurate
• Lower fare basis code availability does not always translate to lower fares being offered on the website: for instance, K or T availability on seatcounter.com does not mean a lower price than a ticket in even V or G unless a special promotion or sale is currently running...I think
• All of the above is my best guess based on available information...I don't have full knowledge of this stuff.