Opinions — Thursday, June 18, 2026

The Federal Circuit reversed and remanded the Western District of Washington's grant of IPR estoppel under 35 U.S.C. § 315(e)(2), which had barred Valve Corporation from asserting two invalidity grounds—one based on Kotkin and another based on Willner-Koji-Raymond—against claims 2, 4, 7, 9–11, and 18 of Ironburg Inventions Ltd.'s U.S. Patent No. 8,641,525, directed to video game controllers with back controls. The district court had concluded that these grounds "reasonably could have raised" in Valve's 2016 IPR petition because a skilled searcher conducting a diligent search reasonably could have been expected to discover the references. The Federal Circuit held that the district court erred as to Kotkin by relying on insufficient evidence: merely showing that Valve's pre-petition classification searches encompassed the codes under which Kotkin was indexed, without accounting for the fact that those searches returned 26,333 references, failed to demonstrate reasonable discoverability. As to Raymond, the court found the district court failed to adequately address hindsight bias where the discovery path relied on forward citation searching that included patents issued after Valve's IPR petition.

The decision clarifies that IPR estoppel under § 315(e)(2) requires the patentee to prove not just that a reference falls within classifications or search strings a petitioner used, but that a skilled searcher exercising reasonable diligence would have actually discovered the reference through reviewable results—though the court declined to establish a bright-line rule requiring manual review in all cases. The opinion leaves unresolved whether the skilled searcher inquiry presents a question of law or fact, and whether "discovery" requires reading and understanding a reference or merely locating it. Judge Stark concurred separately, signaling potential doctrinal tensions in applying the skilled searcher standard. The remand gives the district court another opportunity to evaluate whether the evidence meets Ironburg's burden, with particular attention to whether search results were sufficiently narrowed to permit reasonable discovery and whether post-petition information improperly influenced the analysis.