Revised plans for a 2.5-million-square-foot development at Boston’s South Station would include up to 550 residential units along with a 360-room hotel, office space and retail.

Hines Interests LP and its recently-added investment partner, Gemdale Properties and Investment Corp., are moving forward on the long-stalled air rights project that would be built above the Atlantic Avenue transit hub.

The revised plans by Pelli Clarke Pelli architects reflect the strong demand for luxury housing downtown.

The project would kick off with a 43-story tower built directly behind the Michael S. Dukakis Transportation Center at the South Station headhouse, containing 711,000 square feet of office space on the first 27 floors and 175 condominiums or apartments on floors 28 through 32. The tower would contain both ground-floor lobbies and a “Sky Street” level on the ninth floor with restaurants and retail space and connections to two towers to be built in subsequent phases.

Previously, the first phase would have only included office space.

The second phase would be built above an expanded parking garage and would consist of a 17-story, 438,000-square-foot building with up to 375 residential units, a hotel, or a combination of the two, depending upon market conditions.

The third phase would consist of a 9-story, 511,000-square-foot office building built atop the existing parking garage. And the bus terminal would be expanded by 106,000 square feet.

Developers met with Massachusetts Department of Transportation officials in June to discuss coordination of the project with the South Station Expansion project, which would add seven new tracks to the transit hub for commuter rail and Amtrak service.

Construction of the first phase could begin as soon as next year, pending state and local permitting.