The owner of the largest Passive House office tower in the world has landed a huge refinancing deal three years after the building opened. 

Millennium Partners locked down a $575M securitized loan for the office portion of its Winthrop Center in the Financial District, JLL announced Wednesday. The financing was provided by Morgan Stanley and Barclays.

The mixed-use building is one of the tallest in downtown Boston, at 691 feet. The building includes 824K SF of office space and 317 condominium units.

A JLL team led by Riaz Cassum, Andrew Gray, Robyn King and David Mega represented the borrower in the deal.

"This sizeable commitment from institutional lenders is a testimony to proven sponsorship, the asset's quality and the fundamental strength of both Boston's ultra-luxury condominium and trophy office markets," Cassum said in a statement.

At least 80% of the building has been leased to tenants including Deloitte, McKinsey and M&T Bank. Most recently, energy technology company Schneider Electric signed a 75K SF lease at the building in November, tripling the size of its North American headquarters.

The building was developed to the rigorous Passive House sustainability standard.

The office loan was part of an $856M financing package JLL worked on for Millennium Partners. Earlier this month, the landlord announced it secured a 20-year, $281M C-PACE loan for the residential portion of the property.

That deal, financed by Nuveen Green Capital, represented the largest commercial property assessed clean energy loan ever originated in New England.

The $1.4B tower began construction in 2018 and was completed in 2023. Millennium Partners also owns the 442-unit Millennium Tower and the 256-unit Millennium Place, both in Downtown Crossing.

Winthrop Center's deal comes after another Class-A office building in Boston landed a big refinancing earlier this month. WS Development and PSP Investments secured a $660M loan for their 708K SF One Boston Wharf in the Seaport. The building is fully leased to Amazon.