California Governor Gavin Newsom signed SB 53 on September 29. I think it's a pretty great step, though I certainly hope future legislation builds on it.

I wrote up my understanding of what the text actually does; I welcome any corrections (and certainly further analysis for what this all means for AI safety)!

Very short summary

The law requires major AI companies to:

Publish a frontier AI framework describing how the developer “approaches” assessing and mitigating catastrophic risks, defined as risks of death/serious injury to >50 people or >$1B in damage from a single incident related to CBRN uplift, autonomous crime, or loss of control, and keep the published version of the framework up to date.
Publish model cards summarizing the assessments of catastrophic risks from the model, the role of third parties in those assessments, and how the frontier AI framework was implemented.
Report to California's Office of Emergency [...]

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Outline:

(00:32) Very short summary

(02:22) Longer summary

(02:25) What the bill requires of large frontier developers

(07:38) Other notes about the bill

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First published:
September 29th, 2025

Source:
https://www.lesswrong.com/posts/z5wJMvTafuvBgHnEj/what-sb-53-california-s-new-ai-law-does

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“What SB 53, California’s new AI law, does” by tlevin

LessWrong (30+ Karma)

“What SB 53, California’s new AI law, does” by tlevin