Sam Altman and Elon Musk are hardly strangers. The CEOs of OpenAI and Tesla, respectively, have dined together and shared a stage. They worked together to launch OpenAI in 2015 to counter Google’s dominance in artificial intelligence.

But these days the tech luminaries are not on great terms. They’ve often swiped at each another on social media and in other public venues. So what happened?

Obviously the direction OpenAI has taken plays a role (see below), but Altman described another element to help explain the falling out in a Sunday New York Times article.

“There is disagreement, mistrust, egos,” he told the paper. “The closer people are to being pointed in the same direction, the more contentious the disagreements are. You see this in sects and religious orders. There are bitter fights between the closest people.”

Altman and Musk certainly seemed pointed in the same direction during a dinner in 2015 at the Rosewood Sand Hill, a luxurious ranch-style hotel in Silicon Valley. Google had just acquired DeepMind, a neural networking startup based in London, which made it the most likely company to develop artificial general intelligence, or AGI, a system that can match humans when faced with an unfamiliar task.

At the dinner, the two men, along with others gathered, discussed starting an AI lab that would be transparent, open-source, and dedicated to democratizing the benefits of advance artificial intelligence. Musk and a few other members of the “PayPal mafia”—including Peter Thiel and Reid Hoffman—invested millions to get the lab rolling.

‘Not what I intended at all’

OpenAI launched in 2015, but after a power struggle, Musk parted ways with it in 2018. The nonprofit, needing financial and computing resources, turned to Microsoft, which, starting in 2019, committed to investing billions into it. Altman formed for-profit company under the nonprofit, an unusual structure that contributed to him being briefly fired then rehired as CEO last month.

Since parting ways with OpenAI, Musk has expressed disgust with its direction under Altman, especially after OpenAI accepted billions in investments from Microsoft.

“OpenAI was created as an open source (which is why I named it ‘Open’ AI), non-profit company to serve as a counterweight to Google, but now it has become a closed source, maximum-profit company effectively controlled by Microsoft,” he tweeted earlier this year. “Not what I intended at all.”

Musk has long warned of the potential danger advanced AI poses to humanity, but he also sees its promise if developed safely. Via his startup xAI, last month he announced Grok, an AI chatbot to rival OpenAI’s ChatGPT, the release of which late last year kicked off the current AI boom.

Altman quickly roasted Grok, suggesting on X that it “answers questions with cringey boomer humor in a sort of awkward shock-to-get-laughs sort of way.”

Musk shot back that OpenAI’s GPT-4—which he dubbed “GPT-Snore”—lacks a sense of humor, calling it “about as funny as a screendoor on a submarine.”

Altman called Musk a “jerk” during the On With Kara Swisher podcast, though he acknowledged the role he played in attracting top AI talent to OpenAI. Musk was pivotal to recruiting from Google OpenAI chief scientist Ilya Sutskever, who joined other board members in firing Altman last month, only to backtrack soon after.

Part of feud may stem from Musk’s personality. He’s also traded barbs with Amazon founder Jeff Bezos for years as the two have competed in their space ambitions. And he broke off his friendship with Google cofounder Larry Page, a falling out that he said stemmed largely from Musk poaching Sutskever.

“He has a style that is not a style that I’d want to have for myself,” Altman said of Musk on the Swisher podcast.

But Altman also said that Musk “really does care about a good future with AGI,” which gets back, perhaps, to his more recent comments that “the closer people are to being pointed in the same direction, the more contentious the disagreements are.”

How long their bitter fight continues remains to be seen.