SAN FRANCISCO - OpenAI on Friday officially rejected Elon Musk's nearly 100-billion-US-dollar offer to acquire the nonprofit organization that controls the AI startup.

In a letter to Musk's lawyer Marc Toberoff, OpenAI's attorney, William Savitt, said the OpenAI's board had reviewed the proposal and determined that Musk's bid "is in fact not a bid at all".

The "proposal, even as first presented, is not in the best interest of OAI's (OpenAI, Inc.) mission and is rejected," Savitt wrote. "The decision of the OAI board on this matter is unanimous."

OpenAI Chairman Bret Taylor said in a statement that the company "is not for sale".

"Any potential reorganization of OpenAI will strengthen our nonprofit and its mission to ensure AGI (artificial general intelligence) benefits all of humanity," he wrote.

A team of investors led by Musk on Monday submitted a 97.4-billion-US-dollar bid to buy the nonprofit that controls OpenAI.

The Musk-led team positioned the move as an effort to refocus OpenAI on open-source AI.

"It's time for OpenAI to return to the open-source, safety-focused force for good it once was. We will make sure that happens," Musk said in a statement.

Musk co-founded OpenAI in 2015 alongside Sam Altman and others but left it in 2018. In November 2024, Musk's legal team filed a motion for an injunction as part of a lawsuit against OpenAI, challenging its effort to transition from nonprofit status.

OpenAI has been trying to convert into a for-profit entity. SoftBank is close to finalizing a 40-billion-dollar primary investment in OpenAI at a 260-billion-dollar valuation, according to a report by CNBC earlier this month.