Deliberations begin Monday in the blockbuster trial pitting Elon Musk against AI giant OpenAI and its CEO Sam Altman, whom Musk accuses of abandoning the company's founding mission.

The three-week trial in Oakland, outside San Francisco, has seen a parade of Silicon Valley titans take the stand, with Musk arguing that OpenAI's pivot to a profit-driven business betrayed its original nonprofit mandate.

The world's richest person is suing OpenAI over its transformation from a scrappy nonprofit into the $850 billion juggernaut behind ChatGPT.

If successful, Musk's lawsuit could deal a lethal blow to OpenAI, which helped trigger the AI revolution with its release of ChatGPT in 2022 and is now one of the world's most valuable private companies.

Musk claims Altman and co-founder Greg Brockman improperly used a $38 million donation he had intended to sustain OpenAI as a research lab devoted to developing AI for the benefit of humanity.

For the nine-person jury, as Judge Yvonne Gonzalez Rogers noted, the decision may come down to a simple question: who to believe among the bickering billionaires?

"A non-profit devoted to the safe development of artificial intelligence, open sourced as practical, for the benefit of humanity. You know, we're supposed to buy that," Musk attorney Steven Molo said in his closing argument Thursday, slamming Altman's integrity.

OpenAI attorney Sarah Eddy countered with an attack on Musk himself.

"Even the people who work for him, even the mother of his children, can't back his story," she said, referring to Shivon Zilis, a business associate of Musk with whom he has four children, who testified about her role as an intermediary between the tech executives.

Musk left OpenAI in 2018 and has since pursued AI projects through his rocket company SpaceX, while his AI startup xAI has struggled to gain traction against OpenAI and Anthropic, another prominent California-based AI company.

Closing arguments centered heavily on Altman's integrity and behind-the-scenes maneuvering that rankled colleagues.

Fired unexpectedly in November 2023 by OpenAI's board for a lack of candor, he was reinstated under pressure from employees, but allegations of manipulation and a toxic culture dogged him throughout the trial.

The jury must first resolve a threshold issue: whether Musk, who filed suit in 2024, four years after his last contribution -- did so within the statutory time limit. If not, the case ends there.

The judge ruled that the jury's verdict on this point would be advisory, but said she would likely follow its recommendation.

Should the case proceed, jurors, and ultimately the judge, will determine whether OpenAI's co-founders misappropriated Musk's $38 million in donations and broke a promise to him in order to pursue a commercial path and enrich themselves.

Musk is demanding that OpenAI revert to its nonprofit structure, which would force the company to abandon its planned IPO and unwind ties to major investors, Microsoft, Amazon and SoftBank, who have poured billions into the company amid the global AI race.

The jury will also weigh whether Microsoft, OpenAI's largest private backer with $13 billion committed, knowingly facilitated the shift away from the nonprofit model.