Dropbox has just signed the largest Class-A commercial lease ever inked in San Francisco.

The tech company signed a 15-year lease with Kilroy Realty Corp. for the entire 736K SF office at The Exchange on 16th in San Francisco. This mega-lease follows close behind Facebook’s lease at 181 Fremont for the entire 436K SF of office.

The Exchange on 16th, a four-building complex, is under construction in Mission Bay and Dropbox will occupy the office in three phases starting in the fourth quarter of 2018 through the fourth quarter of 2019.

The $570M LEED Platinum office project was designed by Rios Clementi Hale Studios and offers courtyards, light-filled open office space, rooftop gardens and 14K SF of retail.

The Exchange on 16th is next to the 280 Freeway and near Muni’s T–Line. It is accessible to nearby residential neighborhoods, including Potrero Hill, the Mission District and Dogpatch. The Exchange also is within walking distance of the San Francisco Giants, the new Golden State Warriors stadium and other entertainment.

Other companies involved with the project include Flad Architect as architect of record, general contractor Hathaway Dinwiddie and structural engineer Nishkian Menninger. According to the developer’s website, CBRE has been marketing the office space.