ZeniMax General Manager Matt Firor confirmed TESO's subscription model in an interview with GameStar. "Charging a flat monthly (or subscription) fee means that we will offer players the game we set out to make, and the one that fans want to play," Firor said. "Going with any other model meant that we would have to make sacrifices and changes we weren't willing to make."
Firor was adamant that this was the right move for the game. "The Elder Scrolls Online was designed and developed to be a premium experience: hundreds of hours of gameplay, tons of depth and features, professional customer support -- and a commitment to have ongoing content at regular intervals after launch. This type of experience is best paired with a one-time fee per month, as opposed to many smaller payments that would probably add up to more than $14.99/month any way."
TESO will offer 30 days of play with the purchase of the client. The subscription price will be $14.99/€12.99/£8.99 a month, and Firor said that the studio will announce pricing discounts in the future.
[Update: Fixed quotation.]