Cambridge’s newest luxury apartment complex, the 355-unit Twenty 20 NorthPoint, has opened at 20 Child St.

A ribbon-cutting ceremony was held Wednesday for the 20-story tower, which is part of the planned 5.2-million-square-foot NorthPoint mixed-use development.

Boston-based HYM Investment Group LLC and Canyon Johnson Urban Fund III are partnering on the project designed by CBT Architects and built by John Moriarty Assoc.

During today’s event, a stairway that connects the development to the Gilmore Bridge and the MBTA’s Orange Line was scheduled to be dedicated in memory of Brian P. Murphy, the Cambridge assistant city manager who died Feb. 5.

“The staircase will play a central role in creating a new connection between Charlestown and Cambridge and between the Orange Line and the Green Line,” Thomas N. O’Brien, managing director of The HYM Investment Group LLC, said in a statement. “It embodies the late Brian Murphy’s leadership philosophy, which was central to how he related to the people of this city.  We are honored to speak to that legacy by dedicating this staircase to him.”

The Bozzuto Group will serve as leasing and management company for the apartment complex, which includes high ceilings, oversized windows and high-end fixtures. Community amenities include a bicycle garage, rooftop terrace, fitness center, indoor basketball court, and fourth-floor courtyard with outdoor fireplace and deck.

Twenty|20 includes 41 affordable units, 8,600 square feet of retail space and 184 parking spaces, in addition to its 314 market-rate rental units, which are split among studios, lofts, and one, two and three-bedroom apartment units.