California and New York are advancing a new approach to curbing untraceable 3D-printed "ghost guns" by regulating the printers themselves rather than the digital blueprints, which courts have largely shielded as protected speech. The proposed rules would require 3D printers to run "print blocker" software that scans blueprints and halts any job it identifies as a firearm before printing begins. The shift matters because it could finally give regulators an enforceable tool against homemade weapons — but critics warn it risks laying the groundwork for a much broader system of file surveillance.

The push follows high-profile cases, including the December 2024 killing of UnitedHealthcare chief executive Brian Thompson, allegedly using a partly 3D-printed pistol and suppressor. Neither state specifies what the blocking technology must look like, leaving its scope uncertain. California's AB 2047 would have the state's Department of Justice maintain an approved roster of compliant printers, ban non-listed models sold after 1 March 2029 (with penalties up to $25,000 and an exemption for Hollywood prop-makers), and criminalise disabling the software; it has passed the Assembly but still needs Senate approval and the governor's signature. New York signed a similar measure into law in late May, with Governor Kathy Hochul calling printed gun parts the country's "fastest growing gun safety threat".