A lawsuit between two of Silicon Valley’s biggest tycoons goes to trial Monday in California, the culmination of a years-long bitter feud. Elon Musk has accused Sam Altman of betraying the founding agreement of the non-profit they started together, OpenAI, by changing it to a for-profit enterprise.

Musk accuses Altman, OpenAI, its president Greg Brockman, and its major partner Microsoft of breach of contract and unjust enrichment in the lawsuit. Jury selection is scheduled to begin Monday morning at a federal courthouse in Oakland, with opening arguments from both sides expected later this week. The trial is slated to last two to three weeks. Along with internal communications from Musk and key executives at OpenAI, the trial promises a who’s who of Silicon Valley on the witness stand, including Musk, Altman and Microsoft CEO Satya Nadella.

OpenAI has vehemently denied Musk’s allegations, saying that he agreed in 2017 that establishing a for-profit entity would be a necessary next step for the company and that Musk is “motivated by jealousy” and “regret for walking away”. The company also contests that Musk’s funding was an investment, stating that it was instead a tax deductible donation to the non-profit and does not entitle him to ownership in OpenAI.

The case carries sizable stakes for OpenAI, which is expected to go public later this year at around a $1tn valuation. Musk is seeking a range of remedies that include the removal of Altman and Brockman and more than $134bn in damages, which the tycoon says would be redistributed to OpenAI’s non-profit arm. He also wants to reverse the company’s restructuring as a for-profit entity.

Altman, Musk and several other founders launched OpenAI in 2015 as a non-profit organization, with Musk providing about $38m. Altman’s relationship with Musk turned sour around 2017, after the billionaire grew impatient with OpenAI’s progress and made a failed bid to exert more control over the company. He left OpenAI’s board in 2018 and did not offer any more funding.

During OpenAI’s post-Musk years, it launched the wildly successful ChatGPT, raised tens of billions of dollars from Microsoft and grew to be one of the world’s most valuable private companies. Altman became the face of the AI boom. As the startup sought even more investment in 2025, it gained final approval from regulators to restructure its main business into a for-profit corporation, though one technically still overseen by the original non-profit.

Musk’s suit alleges that Altman’s dealmaking and maneuvering of OpenAI break with the fundamental mission of the company as a non-profit to benefit humanity and amount to a breach of contract. The suit also claims Altman and Brockman unjustly enriched themselves through their control of the company.