OAKLAND, California — Elon Musk is set to testify in court as soon as Tuesday in his legal showdown against Sam Altman.

The outcome of the trial could determine the future of OpenAI, the tech giant that the two billionaires co-founded as a nonprofit in 2015. Musk, who left the board of OpenAI in 2018, seeks to stop the ChatGPT maker from becoming a for-profit company — having publicly accused OpenAI of becoming a “closed source, profit-maximizer.”

“Without Elon Musk there would be no OpenAI, pure and simple,” Steven Molo, Musk’s lawyer, told the court in his opening argument on Tuesday.

Jury selection wrapped up on Monday for a trial scheduled to run for four weeks. Witnesses are expected to include not only Musk, the CEO of xAI, Tesla and SpaceX, and Altman, the CEO of OpenAI, but possibly also Microsoft CEO Satya Nadella, top AI researchers, and current and former OpenAI board members.

OpenAI completed its restructuring in October. Its reimagined for-profit entity, which continues to be controlled by a nonprofit foundation, removed its profit cap and later raised $122 billion in its latest funding round. Musk, in his lawsuit against Altman, has claimed that OpenAI’s transformation “requires lying to donors, lying to members, lying to markets, lying to regulators, and lying to the public.”

Musk, who claims OpenAI benefited from his money, advice, recruiting efforts and connections, is now seeking an estimated $134 billion in damages.

Altman’s side, meanwhile, has claimed that Musk never gave OpenAI the $1 billion he’d promised, alleging that Musk quit when Altman and fellow co-founders Greg Brockman and Ilya Sutskever refused to “bow to Musk’s demands for control of the enterprise or, alternatively, its absorption into Musk’s electric car company, Tesla.”

“ChatGPT drew a new spotlight onto OpenAI,” Altman’s lawyers wrote in a counterclaim, citing the 2022 explosion of generative AI that was driven by the launch of ChatGPT. “Musk had nothing to do with it.”

The lawsuit is the culmination of Musk’s long-standing feud with Altman, which had been simmering even before they became rival tech executives in the AI space. Both were in the courtroom for the first day of arguments on Tuesday.

The trial is taking place just across San Francisco Bay from OpenAI’s headquarters.