California Governor Gavin Newsom vetoed a bill aimed at addressing the potential catastrophic risks posed by highly advanced artificial intelligence models. The governor conceded that the bill addresses a legitimate concern but argued that it doesn’t provide the appropriate regulatory framework.

“I do not believe this is the best approach to protecting the public from real threats posed by the technology,” he wrote. “Ultimately, any framework for effectively regulating Al needs to keep pace with the technology itself.”

The bill, SB 1047, was one of the most controversial pieces of AI legislation this session. Had Governor Newsom signed it, the bill would have required AI developers to submit safety plans to California’s attorney general, who could then hold them liable if their AI models caused harm or posed an imminent threat to public safety.

Proponents of the bill cautioned that without regulation, advanced AI models could potentially be used to develop chemical or nuclear weapons, resulting in mass casualties.

Among them were more than 125 Hollywood actors, directors, producers, music artists, and entertainment industry leaders who signed a letter last week urging Gov. Newsom to sign the bill. Signatories of the letter include J.J. Abrams, Shonda Rhimes, Judd Apatow, Ava DuVernay, Mark Hamill, Jane Fonda, Mahershala Ali, Mark Ruffalo, and SAG-AFTRA President Fran Drescher.

“Grave threats from AI used to be the stuff of science fiction, but not anymore,” the letter reads. “Even though the billionaire opponents of SB 1047 dismiss these concerns as fantastical, many of the industry’s leading engineers, academics and policymakers warn otherwise.”

On the other hand, opponents of the bill, like tech giants l Meta, OpenAI, and the tech industry group Chamber of Progress, argued that stringent regulations would stifle AI innovation and drive companies out of California. The Chamber even released an AI-generated rock song about the bill, featuring lyrics such as “veto the chains that hold us down.”

Newsom did sign another AI bill, AB 2013, which mandates AI developers to disclose whether their models are being trained on copyrighted material.