Seeing as how there is no longer a Super Street Fighter IV forum, I guess this would go here.
Owners of Super Street Fighter IV can now download Arcade Edition, featuring 4 new fighters and fighter changes/balances from the arcade cabinet version of the game.
You can get yours here, or via the in-game marketplace.
And if you want to view replays of the new fighters before you buy, you will need to download the Update Kit, found here (also available through the in-game marketplace.)
*If you download AE, you dont need the kit, FYI
A full retail release will be available as a standalone title on June 24th, for those that don't have SSFIV, or don't bother wilth DLC.