TERA is officially going free-to-play this February. The exact date has yet to be released, but En Masse Entertainment has collected all of the other pertinent details in a lengthy F2P FAQ that you can find on the official website.
The new game service will feature three tiers: Founder, Elite, and Standard. Standard is TERA's free offering, while Elite is the usual $14.99 per month subscription option. Founder status is acquired by purchasing and redeeming a copy of the game and is good for life. Some of the free-to-play limitations include character slots (two per server with the option to purchase more), bank slots (72 with the option to purchase more), and various brokerage fees and taxes. There are no race, class, or content limitations, although Elite players do get dungeon cooldown bonuses.
A full list of account tier differences may be found in the official FAQ. You can also check out the F2P announcement trailer after the cut.