A decade ago, Elon Musk and Sam Altman bonded over a shared concern about the dangers of artificial intelligence. That led them in 2015 to create OpenAI, a nonprofit A.I. lab that had the aim of benefiting humanity.

In 2018, Mr. Musk departed OpenAI after a power struggle with Mr. Altman. Mr. Musk later expressed dismay that the lab had turned into a for-profit company. Over the years, the two men have increasingly made barbed comments about each other, including when Mr. Altman was briefly ousted from OpenAI in November before being reinstated.