MOUNTAIN VIEW — OpenAI has leased a Mountain View office hub that will allow the artificial intelligence company to employ several hundred people and launch a major expansion into Silicon Valley.

The company officially signed a rental agreement to occupy office buildings totaling roughly 439,000 square feet at 350 and 380 Ellis St., according to documents filed Wednesday with the Santa Clara County Recorder’s Office.

“This decision by OpenAI to make this big move will open the way for more AI companies to expand in Silicon Valley rather than in San Francisco,” said David Sandlin, an executive vice president with commercial real estate firm Colliers. “You definitely see tech companies take a bandwagon approach.”

Newmark commercial real estate executives Phil Mahoney, Mike Saign and Jon Mackey represented the property owner in the deal. Newmark and JLL represented OpenAI.

The 350 Ellis St. offices total about 264,700 square feet, while the 380 Ellis site totals about 184,300 square feet, according to Property Shark.

OpenAI leased the buildings for 10 years, county real estate records show. The agreement also allows for two extensions of the original lease — each would be for a period of six years.

The components of the rental agreement that were included in the official filing also indicate that OpenAI could be in a position to greatly cement its presence in Mountain View.

The creator of ChatGPT obtained a right of first refusal to purchase the buildings, real estate documents show.

The filing didn’t reveal additional details of the company’s right to become an owner of the site.

It wasn’t immediately clear on which date the lease commenced, but real estate files show the lease was signed prior to the filing.

The office hub has been described as “exquisite,” according to a brochure circulated for the property.

KKR Real Estate Finance Trust seized ownership of the office hub through a deed in lieu of foreclosure posted in 2024. New York City-based investment firm KKR & Co. Inc. manages the KKR real estate unit.

The foreclosure proceeding placed a value of $120.6 million on the property, one-third of the $357.6 million that a group of real estate investors paid for the site in 2021.

Some signs have emerged lately that suggest office market activity and the overall commercial real estate market in Silicon Valley have begun to rebound in solid fashion.

Major rental deals powered the South Bay office market in 2025 to its best year of leasing activity since the COVID-19 outbreak, commercial real estate firm Savills reported in January.

“Full-year leasing volume for 2025 reached 7 million square feet, the highest level post-pandemic,” Savills stated in the report.

The overall leasing volume in 2025 was 26% higher than in 2024, Savills reported.

The OpenAI lease and other recent AI deals at office sites in downtown Sunnyvale and West San Jose show the office market is not only in recovery mode but is rebounding, Sandlin said.

“Office activity is definitely ramping up in Silicon Valley,” Sandlin said. “The South Bay office market will be much better in 2027 than it is now, and it is better now than it was 12 months ago.”