Boston's 600-foot-tall One Congress tower is less than a year from completion, and it appears close to filling up the majority of its office space.

The development team is in talks with InterSystems Corp. to lease more than 400K SF in the tower, Banker & Tradesman reported, citing two anonymous sources.

Health data company InterSystems was founded in 1978 and is currently headquartered at Cambridge's One Memorial Drive, a 409K SF office tower acquired last year by MetLife Investment Management and Norges Bank. Banker & Tradesman reported that InterSystems is in talks to take the upper floors of One Congress and that the developers are no longer entertaining proposals for large blocks of space, indicating a deal could be close.

The team of Carr Properties, National Real Estate Advisors and HYM Investment Group in January 2019 signed State Street Corp. to move its headquarters to a 510K SF space in the bottom half of the skyscraper. The 43-story, 1M SF project broke ground in June 2019.

HYM and Carr Properties, reached separately by Bisnow Thursday afternoon, declined to comment. InterSystems and CBRE, which is leasing the building on behalf of the developers, didn't respond to requests for comment.

Carr Properties, a D.C.-based developer that built Fannie Mae's new headquarters in 2018, joined on as a development partner for One Congress in September 2018, its first project outside the D.C. area. In July 2019, Carr announced that it increased its ownership stake in One Congress to 75%.

In December, law firm K&L Gates signed a deal to move its Boston office to a 53K SF space in the One Congress tower.

Designed by Pelli Clarke & Partners, One Congress topped off at 600 feet in July, and it is scheduled to be completed in January 2023. It is part of the 2.9M SF Bulfinch Crossing development in Downtown Boston, near the Haymarket MBTA stop.