After being released in South Korea in November last year, Aion Classic was officially launched in the West.
The Aion Classic brings back the original four core classes: Warrior, Scout, Mage, and Priest, with all the balance and progress of the original release, and two upgrades for each class. It has slower progress, past dungeons, and hunting areas back in the past.
Aion Classic is using an "optional subscription" model. You can play for free; but, you are severely limited (to the point where only the most casual of casual players could survive without a sub).
The game will also feature a battle pass (called "Daeva Pass") that has both free and paid reward tracks. While we don't know what the pass includes in NA yet, the KR version of the pass included minor levels of game play advantage such as extra pvp Aion Classic Kinah that can be used towards acquiring better gear.
The cash shop in Korea for Aion Classic thusfar (and the game has been out there since November) has been all cosmetics from what I understand. Now you can buy Cheap Aion Classic Gold on z2u site.