https://www.siliconvalley.com/2021/04/28/ghost-gun-plans-can-be-posted-online-after-court-ruling-2/

Plans for so-called ghost guns can be posted online after a federal appeals court overturned an injunction blocking the move and reinstated a Trump administration order that opened the door to the practice.

The State Department in 2018 removed 3D-printed guns from the Munitions List, and they were placed on the Commerce Control List, which is regulated by the Department of Commerce. That change effectively allowed plans for their construction to be posted online.