US tech entrepreneur Elon Musk, owner of Tesla, SpaceX and X, gestures as he attends the third day of the Atreju 2023 political festival in the gardens of Castel Sant'Angelo, Rome, Italy, 16 December 2023. The Atreju political festival in Rome was organized by Italian Prime Minister Meloni and her right-wing party, Brothers of Italy. The theme of this year's edition is 'Welcome Back Italian Pride' (Bentornato orgoglio italiano). EPA-EFE/ANGELO CARCONI 
The lawsuit said Altman, along with OpenAI's co-founder Greg Brockman, originally approached Musk to make an open source, non-profit company that would develop artificial intelligence technology for the "benefit of humanity".
The Microsoft-backed MSFT.O company's focus on seeking profits breaks that agreement, lawyers for Musk said in the lawsuit.
OpenAI, Microsoft and Musk did not immediately respond to Reuters requests for comment.
Musk co-founded OpenAI in 2015, but stepped down from the company's board in 2018. He also runs the electric vehicle maker TeslaTSLA.O and bought Twitter for $44 billion in October 2022.
ChatGPT, the chatbot from OpenAI, became the fastest-growing software application in the world within six months of its launch in November 2022. It also sparked the launch of rival chatbots from Microsoft, Alphabet and a bevy of startups that tapped the hype to secure billions in funding.
Since its debut, ChatGPT has been adopted by companies for a wide range of tasks from summarizing documents to writing computer code, setting off a race amongst Big Tech companies to launch their own offerings based on generative AI.
(Reporting by Jahnavi Nidumolu in Bengaluru; Editing by Andrew Heavens and Crystal Chesters)