Billionaire entrepreneur says Microsoft-backed company originally promised to make an open-source, non-profit company.

Elon Musk is suing OpenAI and its chief executive Sam Altman, alleging the start-up betrayed its original promise of working to benefit humanity when it forged a multibillion-dollar alliance with Microsoft.

The lawsuit filed in San Francisco on Thursday said Altman and OpenAI’s co-founder Greg Brockman had initially pledged to make an open-source, non-profit company, and that its pursuit of profit constituted a breach of contract.

The company had kept the design of GPT-4, its most advanced AI model, “a complete secret”, said Musk’s lawyers.

Musk co-founded OpenAI in 2015, but stepped down from its board in 2018. He also runs electric vehicle maker Tesla and rocket maker SpaceX, and bought Twitter for $44bn in October 2022.

Last year, entrepreneur Altman was fired by OpenAI’s former board which said it was trying to defend the company’s mission to develop AI that benefits humanity. A few days later, Altman returned to the company with a new initial board.

OpenAI is reportedly planning to appoint several new board members in March.

OpenAI’s chatbot, ChatGPT, 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 bevvy of start-ups that tapped the hype to secure billions in funding.