Private equity giant KKR is spending big to get a piece of Boston’s luxury apartment market, paying $332M for a Seaport tower.

KKR closed on the purchase of NEMA Boston at 399 Congress St. last week from Crescent Heights, according to Suffolk County land records. The sale of the 21-story, 414-unit tower, which sold for $802K per unit, is the largest multifamily transaction of the year thus far in Boston.

KKR also secured a $169M mortgage from Capital One on the property, according to public records. Representatives for the parties didn't immediately respond to requests for comment Monday afternoon.

The sale eclipses Blackstone’s $325M purchase of two residential buildings in East Cambridge from AvalonBay Communities last month.

Multifamily values have grown faster than those of any commercial real estate asset class, even industrial, and have been the fastest-growing in the commercial real estate industry, according to a June Real Capital Analytics report. KKR on Monday announced it had acquired a Phoenix multifamily asset and has purchased a combined $1.2B of Class-A apartments over the past 10 months.

KKR also has invested in at least two Boston-based tech companies and lent $375M to BentallGreenOak and Synergy for their purchase of Boston’s Center Plaza, a 741K SF office complex.

Miami-based Crescent Heights delivered NEMA Boston in November. The developer, which has a national portfolio of multifamily and office properties, bought the Seaport site for $36M in 2016 from local developer Denis Dowdle. Crescent built the tower, part of the firm’s NEMA brand, with a $157M construction loan from The Union Labor Life Insurance Co., Suffolk County records show.

Crescent Heights also owns The Regatta Riverview, a 24-story, 436-unit East Cambridge apartment building, and has completed NEMA residences in San Francisco and in a 76-story, 800-unit skyscraper in Chicago.