Governance of the Unmanned Aircraft System (UAS) Control Segment (UCS) Architecture was transferred from the United States Office of the Secretary of Defense (OSD) to SAE International in April 2015. Consequently, a subset of the UCS Architecture Library Release 3.4(PR) has been published under SAE as the Unmanned Systems (UxS) Control Segment (UCS) Architecture, AS6512. This Version Description Document (VDD) describes the correspondence and differences between the two architecture libraries.