Boston Global Investors, the development firm that led the master planning for the 6.3-million-square-foot Seaport Square development in Boston, has sold 55 Seaport Blvd.

The 13,400-square-foot office and retail building includes its own headquarters.

Zurich Alternative Asset Management paid $23.5 million for the 13,400-square-foot building, or nearly $1,754 per square foot.

Completed in 2016, the building is 100 percent leased including a Capital One branch and 360 Cafe filling the ground-floor retail space.

Newmark Knight Frank’s capital markets team in Boston represented the seller.

“55 Seaport Blvd. represents an exceptional ‘bite-sized’ investment in one of Boston’s most active development districts,” Matthew Pullen, Newmark executive managing director, said in a statement.

Newton-based WS Development is leading the development of the remaining 12.5 acres in the master-planned district after acquiring the remaining undeveloped parcels from BGI in 2015 for $359 million.