Following high-profile testimony from billionaire Elon Musk last week, one of OpenAI's co-founders will testify Monday in the California lawsuit brought by the world's richest man against the creators of ChatGPT. Musk is seeking to force his rivals in artificial intelligence (AI) development to revert to a non-profit foundation.OpenAI CEO and co-founder Sam Altman, who in 10 years has gone from being Musk's protege to a bitter rival, is not expected to take the stand until the week of May 11.