IPR proceedings are formal administrative adjudications subject to the procedural requirements of the Administrative Procedure Act (APA). One such requirement is that “[p]ersons entitled to notice of an agency hearing shall be timely informed of … the matters of fact and law asserted.” In Belden Inc. v. Berk-Tek LLC, 805 F.3d 1064 (Fed. Cir. 2013), the Federal Circuit interpreted this to bar the PTAB from changing theories in the middle of an IPR trial without giving reasonable notice of and an opportunity for the parties to respond to the new theories. The court left unresolved, however, just how much notice and how much of an opportunity to respond the APA requires. A recent Federal Circuit decision gives some clues as to how the court will resolve those open questions.