The report cites a memorandum of lease filed in New York City records as showing that Castle Hook has signed a 15-year lease covering the entire 52nd and 53rd floors of the 53-storey development.

Financial terms have not been disclosed, although rents for the tower’s upper floors are reportedly being marketed at as much as $400 per square foot. The agreement also includes options for a further 10 years.

Castle Hook currently lists its headquarters at 767 Fifth Avenue, the building commonly known as the General Motors Building. It has not been disclosed whether the new agreement represents a relocation or an expansion of the hedge fund’s existing office footprint.

The lease adds to a growing concentration of investment firms at 625 Madison Avenue, which is being developed by Related as a major new office tower on Manhattan’s Upper East Side.

Global investment firm General Atlantic announced earlier this month that it would take 152,000 square feet across five floors at the development, becoming a major anchor tenant. Private equity firm Veritas Capital has also been linked to approximately 92,743 square feet at the property, according to a recent Colliers Manhattan office market report.