The world's largest owner of commercial real estate is getting ready to take more space for its own workers.

Blackstone is finalizing a deal to expand its headquarters at Rudin’s 345 Park Ave. from 750K SF to just over 1M SF, one of the largest office leases in Manhattan in recent years.

The deal would entail Blackstone extending its lease by about six years through the end of 2034. The company has long been based out of the 44-story tower — it first leased 70K SF there in 1988. With the expansion, it would occupy 28 floors, or roughly 55%, of the massive Midtown building.

Blackstone's expansion will coincide with upgrades at the 1.9M SF tower, which opened in 1969, including adding a fitness center. Business Insider first reported the deal.

“We are expanding our commitment to our New York-based workforce, Midtown Manhattan and New York City with this extension,” a Blackstone spokesperson told Bisnow in a statement. “The Rudin organization continues to be a wonderful long-term partner to our firm. We are excited that 345 Park Avenue will remain our global headquarters.”

Blackstone has quickly grown its workforce since 2020, going from 3,165 to 4,735 employees at the end of last year. To house its employees, the firm has reportedly been on the search for 1.5M SF.

With this transaction, Blackstone becomes New York City’s seventh-largest office tenant, with 1.4M SF, according to the firm's spokesperson.

In 2022, Blackstone added 200K SF to its Midtown office at 601 Lexington Ave., bringing its total occupancy in the building to 330K SF. The deal was among the biggest office leases that year.

It also last expanded at 345 Park Ave. not too long ago. The firm took over an additional 80K SF in 2021.

“For over 30 years, Blackstone has proudly maintained its global headquarters at 345 Park Avenue, and we look forward to continuing this strong partnership,” a Rudin spokesperson said in a statement. “The decision of a premier financial services firm such as Blackstone to extend and expand its footprint is a testament to the long-term resiliency of New York City.”

But Blackstone still has its eyes on growth. The company is considering a deal to anchor a new office tower, Business Insider reported, similar to JPMorgan Chase's under-construction supertall at 270 Park Ave. or Citadel's deal to take 800K SF across the street from Blackstone HQ at 350 Park Ave.

UPDATE, JUNE 13, 8:55 A.M. ET: This story has been updated to include a statement from Rudin.