Downtown Boston’s 100 Summer St. tower has landed another major tenant.

Coworking firm WeWork has signed a lease for 117,000 square feet across three floors in the Financial District tower, the company said in a statement. The location, which will hold around 2,300 desks, is projected to open in the fourth quarter of this year.

WeWork occupies 1.2 million square feet at 12 locations in the area, and has been scouting for spaces to fit its new “Headquarters By WeWork” model, as Banker & Tradesman reported earlier this year. Coworking now makes up around 3.2 percent of the region’s office market, occupying 2.6 million square feet in Boston, Cambridge and Somerville, according to Avison Young.

The building already has multiple amenities including a wellness center with bike racks, gym equipment and private showers.

“In our recent impact report, we estimate that 49 percent of WeWork members in Boston said that WeWork has helped their company accelerate its growth,” Dave McLaughlin, WeWork’s general manager for the Tri-State, Northeast and Mid-Atlantic areas, said in a statement. As we open more locations downtown, we’re creating a concentrated and powerful support system for our community, providing more opportunity for the type of collaboration and connection needed to succeed.”

Cambridge biotech Ironwood Pharmaceuticals recently announced it was moving its headquarters to 100 Summer St., leasing 39,000 square feet. The tower is also home to a second co-working firm, a 28,000-square-foot Industrious office.