As it prepares to begin vertical construction of its Winthrop Center tower, developer Millennium Partners is scaling back its luxury condo component from 500 units to 387.

The developer Monday submitted updated plans for the 53-story tower at 115 Federal St., which broke ground last October with foundation work and underground garage construction.

The new filing reflects Winthrop Center’s most up-to-date designs as Millennium seeks a building permit, Joseph Larkin, a principal with Millennium Partners, said today.

“We’re describing the building and how it’s evolved over the past year,” Larkin said. “The city wanted to know what in the program has changed, and the parking got shallower. That initially was part of the concerns of the abutters when we permitted this building a year ago. The city just wants to make sure what the final dimensions of the building are as we are looking for the final sign-off.”

When Millennium was seeking BPDA approval in 2018, owners of two abutting office towers at 75-101 Federal St. and 100 Summer St. warned that Winthrop Center could cause structural damage to their properties. That prompted Millennium Partners to reduce the parking garage from five to four levels, as reflected in the excavation permit that was approved last year, Larkin said.

Equity Office Properties, then the owner of 100 Summer St., warned in March 2018 that its own 1 million-square-foot tower could settle as much as 1.7 inches because of Winthrop Center’s 5-story underground garage, including excavation to a depth of 75 feet. And Boston-based Rockpoint Group, owner of 75-101 Federal St., said at the time that Winthrop Center’s “top-down” construction technique is untested in a Boston high-rise project. The method reduces timelines with simultaneous vertical construction and foundation work.

Millennium Partners commissioned additional geotechnical studies by engineers Haley & Aldrich. In a May 2018 BPDA filing, Millennium said it would increase the thickness of slurry walls to 4 feet, compared with the standard 2 1/2 to 3 feet. And it agreed to install 179 devices on the abutters’ structures to monitor potential cracks, vibrations and tilting.

Rockpoint Group has since acquired 100 Summer St. in a $806 million transaction that closed Oct. 1.

In this week’s notice of project change, Millennium Partners said it’s planning to reduce the tower’s overall square-footage from 1.65 million square feet to 1.5 million square feet, including a 37,285-square-foot reduction in saleable condo space. The overall condo component, including the residential club section, would shrink by 97,175 square feet.

The final condo count may be further revised based upon the size of penthouses and market demand, according to the filing. The office portion on the lower floors would increase from 750,000 to 772,422 square feet, with a floor previously devoted to conference space converted to general office use.

Millennium Partners is seeking a determination from BPDA Director Brian Golden that the changes do not require further review. The project’s impact advisory group will meet from 6-8 p.m. on Nov. 6 at 77 Franklin St. to review the changes.