An Action Closing Prosecution (ACP) is typically issued at specific points in the inter partes reexamination process. According to MPEP 2671.02: 1. When all claims are found patentable in the first action: "When all claims are found patentable in the first action, the examiner will, at that point, issue an ACP, since the patent owner has nothing to respond to." 2. Usually after the second Office action: "Otherwise, it is intended that the second Office action in the reexamination proceeding will ordinarily be an ACP." 3. When issues are clearly developed: "Before an ACP is in order, issues should be clearly developed." The MPEP also notes that "The criteria for issuing an ACP is analogous to that set forth in MPEP § 706.07(a) for making a rejection final in an application." This means that the examiner should have addressed all issues and given the patent owner a fair opportunity to respond before issuing an ACP. To learn more: Action Closing Prosecution ACP timing inter partes reexamination patent examination USPTO procedure