California Gov. Gavin Newsom yesterday signed legislation that would mandate transparency measures from frontier AI companies.

Why it matters: The law will have major implications for the country's biggest AI players — and shows the appetite to regulate AI at the state level.

The Trump administration and key Republicans have advocated for a pause on AI laws and regulation coming out of the states.

What's inside: The Transparency in Frontier Artificial Intelligence Act, authored by state Sen. Scott Wiener, requires large AI developers to make public disclosures about safety protocols and to report safety incidents.

Anthropic was the only major AI company to publicly support the bill.

What they're saying: "This bill will strengthen California's ability to monitor, evaluate, and respond to critical safety incidents associated with these advanced systems," Newsom wrote.

"With this law, California is stepping up, once again, as a global leader on both technology innovation and safety," Wiener said.

Anthropic's head of policy, Jack Clark: "While federal standards remain essential to avoid a patchwork of state regulations, California has created a strong framework that balances public safety with continued innovation."

Newsom also addressed the possibility of any federal effort to preempt state law in his signing message.

"Should the federal government or Congress adopt national AI standards that maintain or exceed the protections in this bill, subsequent action will be necessary to provide alignment between policy frameworks — ensuring businesses are not subject to duplicative or conflicting requirements across jurisdictions."

Flashback: Last year, Newsom vetoed an AI safety bill that was designed to have first-in-the-nation safety regulations against AI misuse.