OpenAI, the influential artificial intelligence company that ousted and then reinstated its high-profile chief executive three months ago, faces a new drama: a lawsuit from Elon Musk, one of the richest men in the world and a co-founder of the A.I. lab.

Mr. Musk sued OpenAI and its chief executive, Sam Altman, accusing them of breaching a contract by putting profits and commercial interests in developing artificial intelligence ahead of the public good. A multibillion-dollar partnership that OpenAI developed with Microsoft, Mr. Musk said, represented an abandonment of a founding pledge to carefully develop A.I. and make the technology publicly available.

“OpenAI has been transformed into a closed-source de facto subsidiary of the largest technology company, Microsoft,” said the lawsuit filed Thursday in Superior Court in San Francisco.

The 35-page lawsuit is the latest chapter in a fight between the former business partners that has been simmering for years, and it homes in on unresolved questions in the A.I. community: Will artificial intelligence improve the world or destroy it and should it be tightly controlled or set free?

Mr. Musk, the chief executive of Tesla, and Mr. Altman, as much as anyone in the world, have helped to frame that debate. Mr. Musk helped found OpenAI in 2015 as a response to A.I. work being done at the time by Google. Mr. Musk believed Google and its co-founder, Larry Page, were dismissive of the risks A.I. presented to humanity.

Mr. Musk left OpenAI’s board during a power struggle in 2018. The company went on to become a leader in the field of generative A.I. and created ChatGPT, a chatbot that can produce text and respond to queries in humanlike prose. Mr. Musk, who founded his own A.I. company last year called xAI, said OpenAI was not focused enough on the technology’s risks.