OpenAI, one of the darlings of the San Francisco office market, has vacated its headquarters at 3180 Mission St.

An entity affiliated with Elon Musk, a co-founder of OpenAI, placed the building up for sublease this month, the San Francisco Business Times reported.

An unnamed source told the Business Times that OpenAI was leaving the building, also known as the Pioneer Trunk Factory, because of competition with Musk's new artificial intelligence firm, xAI. An OpenAI spokesperson refuted that claim, confirming the company left the office but saying it did so because it outgrew the space.

Musk parted ways with OpenAI in 2018 and filed suit against the company in February, alleging it had shirked its mission and put profit over the public good. In filings made as part of that lawsuit, attorneys for Musk wrote that he was paying monthly rental expenses for the Mission Street space, the Business Times reported.

Musk withdrew that suit in June only to bring it back earlier this month.

Representatives for Musk didn't respond to requests for comment Monday afternoon.

OpenAI made waves in the fall of 2023 when it signed the largest office lease in the Bay Area since before the pandemic. The company took over two buildings from Uber totaling 486K SF. Open AI is also rumored to be interested in leasing 315K SF at 550 Terry Francois.

The company's leases, along with others made by AI firms, have offered a glimmer of hope in the otherwise glum San Francisco office market.

Bisnow reached out to Raise Commercial Real Estate, a tech-centric brokerage firm that has represented OpenAI in its real estate transactions, but didn't receive a response.

JLL, which will handle the subleasing at the Pioneer Trunk Factory, didn't respond to a request for comment.

CORRECTION, AUG. 30, 12:52 P.M. PT: This story has been updated to accurately reflect that OpenAI did not close a lease at 550 Terry Francois in San Francisco.