Here's when Elder Scrolls Online's Thieves Guild DLC will release - CNET

Along with the release date, new details on the content have also be divulged. You can read them below. You can also watch the new trailer above.

• Brand New Story Content: Help restore the Thieves Guild in Abah's Landing, currently besieged by the mercenary force known as the Iron Wheel. After a high-stakes heist gone horribly wrong, the Iron Wheel will stop at nothing to destroy the Guild. Hours of story content await as you solve the mystery of the Iron Wheel and restore glory to the Thieves Guild.
• New Criminal Activities.: Leveraging ESO's Outlaw Refuges, Thieves Guild quests take you all over Tamriel to engage in--and profit from--criminal activity such as stealing, looting, and pickpocketing. Heists, a new quest type, allow you to hone your thieving skills by adding trespassing and stealth/hiding mechanics that enable you to break into warehouses and homes in Abah's Landing to relieve merchants and citizenry of their goods. Beware of the guards!
• New 12-Player Trial: With both Normal and Veteran difficulty modes, the Maw of Lorkhaj 12-Player Trial will test your allies and your courage. Breach the gates of an ancient Khajiiti shrine, and confront the ghostly legions of Namiira in eerie lamp-lit corridors--complete with ruthless new enemies--terrifying bosses, and a wealth of treasure from the depths of Oblivion.
• All-New Skill Line: Want to enhance your character with all-new thieving, sneaking, and stealing-related passive skills? You're in luck! The Thieves Guild in Abah's Landing will teach you these skills as your progress through the ranks of the organization.
• Thieves Guild-Exclusive Rewards and Items: Ea new items through in-game quests and browse Thieves Guild-themed items coming to the Crown Store soon.

The Thieves Guild DLC was first announced during QuakeCon 2015 and is part of developer ZeniMax Online's efforts to keep the game fresh. Another expansion which adds The Dark Brotherhood content is also expected later this year.

The game was released in April 2014 for PC and dropped its compulsory monthly subscription in January 2015. It now has a pay-once model with further support from microtransactions. Console versions of the game debuted on PlayStation 4 and Xbox One in June 2015.