Elon Musk says AI is riskier than nuclear weapons, backs slowdown

Billionaire Elon Musk has thrown his weight behind a call to slow the development of artificial intelligence, reviving his warning that artificial general intelligence carries "significantly higher risk than nuclear weapons" in a weekend that rattled AI stocks worldwide.

Musk, who runs Tesla and SpaceX, reshared the April 2023 post on Sept. 12, the same day Anthropic CEO Dario Amodei published a roughly 3,900-word essay urging the industry to "pace the frontier" so that safety research can catch up with capability. Musk's response on X was three words: "Dario is right."

OpenAI CEO Sam Altman followed within hours. He posted that he agreed with Amodei, said OpenAI would also open its systems to outside evaluators, and told Fortune the company would not pursue its initial public offering this year, calling a listing now "ill-advised" while alignment questions remain open. OpenAI filed its S-1 with the Securities and Exchange Commission in June.

What Amodei proposed

The essay, titled "We Must Pace the Frontier," argued that AI has been advancing far faster since the summer because models are increasingly building the next generation of models. Amodei proposed a three-step plan: slow capability gains, embed third-party evaluators inside labs with deep access, and extend coordination to international limits between democratic and authoritarian governments. He framed it as possible without "sacrificing commercial advantage or the United States' lead in AI."

The debate had already broken into the open. A researcher who had worked at both OpenAI and Anthropic resigned publicly on Sept. 9, accusing both firms of prioritizing speed over safety. Evan Hubinger, an alignment lead at Anthropic, wrote on X that he personally puts the chance of AI causing human extinction above 10% within a decade, while stressing the risk lies in future self-improving systems, not current models. Geoffrey Hinton, the 2024 Nobel laureate in physics, told the BBC a 10% figure was not unreasonable.

Not everyone agreed. President Donald Trump dismissed the CEOs' warning on Sunday, saying a slowdown was unnecessary and would hand China an advantage.

Markets deliver a verdict

Investors reacted on Monday. The PHLX semiconductor index dropped 5.9% in a single session, cutting its 2026 gain to 57%, according to Reuters. The selloff ran from Tokyo to Amsterdam before U.S. markets opened.

Citigroup strategists led by Stuart Kaiser had warned clients a day earlier that a coordinated slowdown could squeeze earnings revisions across technology, compounding pressure from midterm election uncertainty and rising bond yields. Slower frontier development would leave revenue from deployed models intact, they noted, but undercut the growth assumptions baked into valuations.

Nigel Green, chief executive of deVere Group, said the bigger risk is hidden concentration: people who never bought a tech stock now hold large AI positions through pensions and index funds that drifted toward a single theme.

The unity among Musk, Altman and Amodei is unusual for three executives whose companies compete directly. Anthropic is also a major customer of Musk's data center capacity. Whether the statements harden into binding commitments is the question markets are now pricing.