With this newest transaction, which calls for an April 2010 move-in date, Twitter will occupy a total of 63,222 square feet of office space in the building—nearly six-times the size of its previous 11,000-square-foot headquarters' location on Bryant St.

The company needed space that would accommodate its growth efficiently, while at the same time maintaining a central San Francisco location, explains Victoria Burkheimer, vice president of acquisitions for Westcore Properties. "The building's desirable south of Market location, coupled with its high-tech feel including exposed ceilings and creative finishes, were key drawing points for Twitter." She continues.

According to Burkheimer, Twitter was negotiating simultaneously on the sixth and third floors while Westcore worked to facilitate moving existing tenants to make both floors available. "Westcore was able to facilitate the move of Bebo, an existing tenant, from the sixth floor to the second by signing a termination agreement with Moderati who was in the process of trying to sublease its space on the second floor," says Burkheimer. "This created two full floors for Twitter, released Moderati from its lease obligation, and provided Bebo with a more suitable space for its current needs." The building is now at 100% occupancy.