Musk has long feuded with OpenAI chief executive Sam Altman and has filed a number of legal complaints against the company and Altman, claiming that the AI business and its leadership have misrepresented OpenAI as a philanthropy.

Musk claims that OpenAI has broken with its founding charter by seeking to make a profit with its AI tools.

OpenAI is operated by a non-profit organisation that controls an entity called OpenAI LP, a for-profit company that exists within the larger company’s structure.

That for-profit company took OpenAI from effectively worthless to a valuation of around $US100 billion in just a few years — and Altman is largely credited as the mastermind of that plan and the key to the company’s success.

The massive investment from Musk, first reported in the Wall Street Journal, could give Musk majority control of the company, which rivals his X.AI artificial intelligence company.

“If Sam Altman and the present OpenAI, Inc. Board of Directors are intent on becoming a fully for-profit corporation, it is vital that the charity be fairly compensated for what its leadership is taking away from it: control over the most transformative technology of our time,” Marc Toberoff, a lawyer representing the investors, said in a statement.

“It’s time for OpenAI to return to the open-source, safety-focused force for good it once was. We will make sure that happens.”

In response, Altman said in a post on X, “No thank you but we will buy Twitter for $US9.74 billion if you want”.

Musk, who co-founded OpenAI in 2015, has since left over a dispute related to the company’s shift to for-profit work.

OpenAI was founded because its creators believed artificial general intelligence, or AGI, posed a serious threat to humanity.

The company created a board of overseers to review any product the company created, and its products’ code was made public.

Yet a company with big backers, such as Microsoft and venture capital firm Thrive Capital, has an obligation to grow its business and make money.

Investors want to ensure they’re getting bang for their buck, and they’re not known to be a patient bunch.

That could have led Altman to push the for-profit company to innovate faster and go to market with early products.

In the great “move fast and break things” tradition of Silicon Valley, those early products don’t always work so well at first.

That could become a problem when it’s a technology so good at mimicking human speech and behaviour that it can fool people into believing its fake conversations and images are real.

In a bizarre boardroom battle in late 2023, the OpenAI board fired Altman before quickly rehiring him.

The board has since been reshaped, and former directors involved in the decision had said they were concerned OpenAI was moving too quickly without regard for safety.

Musk first sued OpenAI in June 2024, but he dropped that initial lawsuit after the company published a blog post that included several of Musk’s emails from OpenAI’s early days.

The emails appeared to show Musk acknowledging the need for the company to make large sums of money to fund the computing resources needed to power its AI ambitions, which stood in contrast to the claims in his lawsuit that OpenAI was wrongly pursuing profit.

Musk filed a new lawsuit last August and accused OpenAI of racing to develop powerful “artificial general intelligence” technology to “maximise profits”.

Musk also accused the company of engaging in racketeering.

OpenAI, meanwhile, accused Musk of essentially being jealous that he was no longer involved in the startup, after he left OpenAI in 2018 following an unsuccessful bid to convince his fellow co-founders to let Tesla acquire it.