The 4.5 million-square-foot Cambridge Crossing—or CX for short—on a 45-acre parcel where Somerville, Cambridge, and Boston meet is supposed to have 2.1 million square feet of tech and office space in five buildings and as many as 2,400 condos and apartments (as well as 2,500 residences already in the footprint).

There will also be 11 acres of open space, and the project will be near the relocated Lechmere stop that’s part of the Green Line extension.

The plans from San Francisco-based DivcoWest are currently moving through the approval processes in Cambridge, Somerville, and Boston, so a definitive timeline is not yet set; though the company did break ground on a 430,000-square-foot science-and-tech hub there in October 2017.

Developers Boston Properties and Delaware North officially broke ground in January 2016 on the humongous project at the old Boston Garden site along Causeway Street. It continues to unfold.

Ultimately, the development will mean more than 1.5 million square feet of shops, restaurants, offices, hotel rooms, and residences, as well as an expansion of nearby TD Garden and transit improvements to North Station.

Phase I is underway and should wrap in 2018. It is due to include flourishes such as the city’s largest supermarket; a 15-screen movie theater; 10,000 square feet of outdoor space for a new entrance to TD Garden and North Station; and 175,000 square feet of what the developers are calling “creative office space.”

Phase II will include a 440-unit, 38-floor residential tower and a 260-key, 10-floor micro-hotel; and Phase III will be an office tower running to 21 stories.

The 415-foot, 503-unit Avalon North Station officially opened in December 2016, marking the completion of one of the tallest new apartment buildings in Boston and one with significant new public space in the North Station area.

The 38-story tower at 1 Nashua Street—its original name was the Nashua Street Residences—includes flourishes such as a 35th-floor lounge with a game room and a terrace; a 24-hour concierge; a 24-hour fitness center; a pet spa; bike storage; and 220 parking spaces.

The tower was also Boston’s first residential high-rise with so-called destination-controlled elevators, according to developer AvalonBay Communities. The devices basically shepherd users to their floors faster.

Finally, the development came with a public arcade providing airy access to North Station and its Green and Orange lines.

When completed—developer HYM Investment Group says by September 2019—so-called Bulfinch Crossing is expected to include 812 residential units; 196 hotel rooms; 1.15 million square feet of office space; and 85,000 square feet of retail.

The redevelopment on the Government Center Garage will also include around 1,100 parking spaces for residents and the public; and a one-acre “rooftop amenity,” according to an earlier release from the developers.

The first building to go up will be a 45-story, 486-unit apartment building on New Sudbury Street. Bulfinch Crossing will be 558 feet at its highest point.