Shaping the global AI landscape is not just a battle of technical paths, but also a wound of private trauma that has never healed. A lengthy investigative report by Wall Street Journal reporter Keach Hagey, based on extensive interviews with current and former employees, executives, and associates, reveals for the first time the decade-long personal feud between the founders of Anthropic and OpenAI—a rift that not only defined the direction of both companies but also gave birth to one of the world’s leading AI enterprises.

In recent months, Dario Amodei, a key founder of Anthropic, has used far more intense language internally than in his public remarks. He likened the legal dispute between Sam Altman (OpenAI’s leader) and Elon Musk to a "Hitler vs. Stalin" conflict, described OpenAI President Greg Brockman’s $25 million donation to a pro-Trump super PAC as "evil," and compared OpenAI and other competitors to "tobacco companies selling products they know are harmful." After the escalation of a dispute involving the Pentagon, he even referred to OpenAI as "mendacious" on Slack, writing, "These facts suggest a pattern of behavior that I have seen all too often in Sam Altman." Internally, Anthropic frames its brand strategy as creating a "healthy alternative" to competitors, and a subtly mocking ad that ran during this year’s Super Bowl—targeting OpenAI’s decision to include ads in its chatbots—was a public manifestation of this adversarial stance.

The roots of this bitter feud trace back to 2016, in the living room of a shared house on Delano Street in San Francisco, where Dario Amodei and his sister Daniela lived. Greg Brockman, a co-founder of OpenAI, often visited due to his friendship with Daniela, and one day, Brockman, Dario, and Daniela’s then-fiancé—effective altruism philanthropist Holden Karnofsky—sat together debating the right path for AI development. Brockman argued that all Americans should be informed about the forefront of AI progress, while Dario and Karnofsky believed sensitive information should be reported to the government before being made public. This seemingly small disagreement would later become the watershed dividing the philosophical paths of OpenAI and the future Anthropic.

Impressed by OpenAI’s team, Dario joined the company in mid-2016, often staying up late with Brockman to train AI agents to play video games. Yet over the next four years, conflicts over power and belonging deepened. In 2017, Elon Musk—then OpenAI’s main funder—demanded a list of each employee’s contributions and used it to justify layoffs, with 10% to 20% of the 60-person team being let go one by one. Dario viewed this move as cruel, and one of those laid-off employees would later become a co-founder of Anthropic. That same year, an ethics advisor hired by Dario proposed that OpenAI act as a coordinating entity between AI companies and governments; Brockman then extrapolated this idea to "selling AGI to the United Nations Security Council," a notion Dario considered almost treasonous, leading him to briefly contemplate resigning.

In 2018, after Musk’s departure, Sam Altman took over OpenAI’s leadership. He and Dario reached a consensus that employees lacked confidence in Brockman and Chief Scientist Ilya Sutskever’s leadership, and Dario agreed to stay on the condition that the two no longer oversee him. However, he soon discovered that Altman had simultaneously promised Brockman and Sutskever the right to fire him, creating conflicting commitments that eroded trust. As OpenAI launched the development of the GPT series, the most intense conflict erupted within the executive team over who could participate in the language model project: Dario, then the research director, refused to let Brockman intervene. Daniela, who co-led the project with Alec Radford, even threatened to resign from her leadership position, dragging Radford’s personal preferences into the executive proxy war.

Dario’s credentials soared with the success of GPT-2 and GPT-3, but he felt Altman consistently downplayed his contributions. When Brockman appeared on a podcast to discuss OpenAI’s charter—work Dario believed he had contributed more to—he was furious at being excluded. Similarly, he was displeased to learn that Brockman and Altman were meeting former President Obama without inviting him. The conflict escalated dramatically during a confrontational meeting in a conference room: Altman summoned the Amodei siblings, accusing them of inciting colleagues to submit negative feedback about him to the board. The siblings denied the accusation, and when Daniela brought in the executive Altman claimed had provided the information, that executive said they knew nothing about it. Altman promptly denied ever making such a statement, sparking a heated argument.

In early 2020, Altman requested executives to conduct peer reviews, and Brockman wrote a strongly worded feedback accusing Daniela of power abuse and using bureaucratic processes to silence dissent—feedback Altman pre-approved as "tough but fair." Daniela countered each point in detail, escalating the argument to the point where Brockman briefly suggested retracting his comments. By the end of 2020, the team centered around Dario had decided to leave OpenAI; Daniela took the lead in negotiating their departure with lawyers. Altman even visited Dario’s home personally to persuade him to stay, but Dario insisted on only reporting directly to the board and made it clear he could no longer work with Brockman. Before leaving, he wrote a lengthy memorandum dividing AI companies into "market-driven" and "public-benefit-driven" categories, arguing that the ideal ratio was 75% public benefit and 25% market. Several weeks later, Dario, Daniela, and nearly a dozen other employees left OpenAI to found Anthropic.

Five years later, both OpenAI and Anthropic are valued at over $300 billion and are racing toward public listings. At the February AI Summit in New Delhi, when Indian Prime Minister Modi raised his hands high for a group photo with tech leaders, Amodei and Altman chose to sit out, opting instead for an awkward elbow bump—a small, telling gesture of the personal rift that still divides the two companies shaping the future of AI.