Cottonwood Management took the wraps off its new “Echelon” brand scheme – and chef Ming Tsai mixed custom cocktails for the occasion – at the site of a 1.3-million-square-foot residential and retail project that recently began construction in Boston’s Seaport District.

A ceremonial groundbreaking was held Tuesday at the 3.5-acre site at Seaport Boulevard and B Street. Three towers – two containing a combined 448 condominiums and a 285-unit rental building – will rise above a 125,000-square-foot retail podium. The $900 million project will be the Seaport District’s second-largest residential property after the 832-unit Benjamin and Via apartment towers, currently nearing completion on Seaport Boulevard.

Regent Hotels will provide resident services for the condo units.

Kohn Pedersen Fox and CBT Architects designed the complex including 50,000 square feet of amenity space such as two outdoor pools and two roof decks. A condo sales office will open this fall, with completion of the project projected in late 2019 and early 2020. The Collaborative Cos. of Boston has been named sales and marketing agent.

WilliamsNY developed the Echelon name and branding strategy for Los Angeles-based Cottonwood.

Cottonwood acquired the property for $120 million in November 2015 from Seaport Square master developer Boston Global Investors.