Jacob Coxon announced his resignation from Anthropic Tuesday in a chain of posts on X, saying he had spent the past three years conducting pre-training research at the two AI giants.

Coxon worked on OpenAI's technical staff from 2023 until July 2026, when he joined Anthropic as a researcher. During his time at OpenAI, he worked on GPT-4o.

Coxon said Tuesday that both AI companies have failed to fully disclose the extent of their concerns about the technology, warning that neither Anthropic nor OpenAI is "acting responsibly."

"They are racing straight to self-improving superintelligence and gambling with our lives," he wrote.

He argued that researchers and executives at both companies privately harbor far greater fears about AI than they acknowledge publicly.

"The people building AI earnestly believe that it could kill us all by the end of the decade. This is not a marketing stunt," he wrote. "If anything, many executives and senior researchers will couch their phrasing in the press to sound sensible — but I hear the same people express fear privately."

Coxon said the two companies differ in how they view those risks.

"At OpenAI, many have not deeply internalized the civilizational stakes," Coxon wrote in a post. "At Anthropic, the stakes are well-understood, but they are locked in a race to get there first — they believe no one else will act responsibly, so they must do it themselves, despite the risk."

Evan Hubinger, an Anthropic employee who leads the company's alignment stress testing team, appeared to agree with Coxon, responding to his post on X.

"Jacob is correct here—we really do earnestly believe AI could kill all humans!" Hubinger wrote, adding that he personally believes there is more than a 10 percent chance AI could cause human extinction within the next decade.

While he said Anthropic is "trying its best," the current employee further argued that the company does not yet have a plan to solve alignment for superintelligent AI and is "not clearly on track to."

His warnings come amid a string of departures from AI companies by researchers who have raised concerns about the industry's approach to safety.

Former OpenAI alignment chief Jan Leike left the company in 2024, saying he had reached a "breaking point" with leadership and arguing that "safety culture and processes have taken a backseat to shiny products," according to a Business Insider report.

Anthropic has faced similar departures. Safeguards researcher Mrinank Sharma left in February, saying he had repeatedly seen how difficult it was for the company to let its stated values guide its actions.

OpenAI researcher Hieu Pham also announced his departure in February after saying he could "finally feel the existential threat that AI is posing," according to Business Insider.

Recent incidents have further intensified concerns. OpenAI disclosed in July that its models escaped a test environment and hacked into Hugging Face's systems, calling the incident a "warning shot."