Musk's lawsuit alleges OpenAI ditched its mission to build artificial intelligence for the public good, and he is seeking billions of dollars and a change in management and direction for OpenAI, which says Musk knew exactly what was going on and was angry he was not made CEO.
William Savitt, a lawyer for OpenAI, told Musk his questions about the tax benefits of his $US38 million in donations to OpenAI and the company's corporate structure were meant to be simple, and that Musk's responses should be as well.
"Your questions are not simple. They're designed to trick me," Musk, the CEO of Tesla and SpaceX, told a nine-person jury in Oakland, California, federal court.
The heated exchange came after Musk, over two days of questioning by his own lawyer, accused OpenAI, its co-founder and chief executive Sam Altman, and its President Greg Brockman of promising to build a nonprofit to develop AI responsibly, before pivoting to create a for-profit entity in 2019 to enrich themselves.
OpenAI has argued Musk, who helped finance the company's early growth, is driven by a compulsion to control it and bitterness over its success after he left the board in 2018. It has said he is seeking to bolster his own AI company, SpaceX unit xAI, which lags OpenAI in user adoption.
The company also contends Musk pushed OpenAI to become a for-profit business, wanted to become CEO, and that safety was not a priority for him when he was with the company.
Savitt asked Musk about an email he sent Altman in 2015 suggesting OpenAI be structured as a for-profit corporation with a parallel nonprofit, part of an effort to show Musk was supportive of a for-profit entity. Musk said the emails did not indicate his definitive position.
"Discussions and brainstorming are not a deal," said Musk, wearing a dark suit over a white shirt and glancing at the jury occasionally as he spoke.
Seated in the courtroom audience, Altman and Brockman - who took notes with a red-ink pen on a yellow legal pad - listened intently as the exchanges between Musk and Savitt grew increasingly heated.
Musk repeatedly asked Savitt to stop interrupting him. Musk answered one of Savitt's questions by saying, "You tell me." Savitt responded, "I get to ask the questions, Mr Musk."
Musk is expected to return to the stand for more cross-examination on Thursday.
The trial highlights the depth of the rupture between Musk and Altman. The pair co-founded OpenAI in 2015 to create a benevolent steward of the technology and fend off rivals such as Alphabet's Google. Musk testified he left OpenAI in 2018 to focus on Tesla and SpaceX.
Microsoft, also a defendant, invested $US10 billion in OpenAI in 2023, a deal Musk said fuelled his concerns that OpenAI was abandoning its mission.
Musk is seeking $US150 billion in damages from OpenAI and Microsoft, with any award going to OpenAI's charitable arm. He also wants OpenAI to revert to a nonprofit, with Altman and Brockman removed as officers and Altman removed from the board.
His claims include breach of charitable trust and unjust enrichment.
