In St. Regis Mohawk Tribe v. Mylan Pharm. the Fed. Cir. affirmed the PTABs denial of St. Regis's motion to terminate IPRs filed by Mylan based on sovereign immunity.  Using a framework of IPRs being a hybrid proceeding with adjudicatory characteristics  but also more like a specialized agency proceeding, the Fed. Cir ultimately concluded that an IPR is more like an agency enforcement action than a civil suit based on 1) the Director's discretion on how IPRs are conducted, 2) the ability for the director to participate in an appeal when a private challenger drops out, and 3) the dissimilarities between the USPTO procedures and the FRCP. In his concurrence, Judge Dyk wrote to describe in greater detail the history of inter partes review proceedings, history that confirms that those proceedings are not adjudications between private parties. While private parties play a role, inter partes reviews are fundamentally an agency reconsideration of the original patent grant, proceedings as to which sovereign immunity does not apply.