“A lot of compute is needed,” Mr. Musk said in a post about the financing, in which BlackRock, Fidelity and Sequoia participated.

The artificial intelligence company founded by Elon Musk, xAI, said on Monday that it had raised $6 billion, giving the start-up a major lift as it competes with rivals, including OpenAI.

The company said on its website that it would use the money to continue building its infrastructure and accelerate research and development. BlackRock, Fidelity, Sequoia Capital and others participated in the funding round.

“A lot of compute is needed,” Mr. Musk said of the investment round in a post on X.

The fund-raising could value xAI at $35 billion to $40 billion, up from $24 billion earlier this year, The New York Times previously reported.

Mr. Musk and xAI did not immediately respond to requests for comment.

Mr. Musk is trying to play catch up on A.I. The billionaire, who also leads other companies, including Tesla, X and SpaceX, publicly debuted xAI last year, well after a boom in the A.I. industry spawned dozens of products that could create text, images and even videos.

Mr. Musk quickly built what he said would be the world’s largest supercomputer in Memphis, which powers Grok, xAI’s chatbot. Grok is available to subscribers on X.

Mr. Musk helped found OpenAI, but walked away from it in 2018 after disagreements with other co-founders, including Sam Altman, its chief executive.

Mr. Musk has sued OpenAI to block it from transforming itself from a nonprofit into a for-profit company, saying that Mr. Altman and another co-founder, Greg Brockman, had breached the company’s founding contract by putting commercial interests before the public good. OpenAI has argued that the lawsuit is an attempt to hamstring the company while Mr. Musk builds a rival.

(The New York Times has sued OpenAI and Microsoft for copyright infringement of news content related to A.I. systems. OpenAI and Microsoft have denied those claims.)

Mr. Musk has argued that A.I. could destroy humanity, but that he has the ability to build it more safely.

To jump-start xAI, Mr. Musk has trained its A.I. on data from X. Several investors in Mr. Musk’s bid to acquire X in 2022 have also provided funding for the A.I. start-up, including the venture capital firm Andreessen Horowitz and the Saudi Arabian prince Alwaleed bin Talal’s investment company, Kingdom Holding. In total, xAI has raised more than $12 billion.