Case Explained: IRONBURG INVENTIONS LTD v. VALVE CORPORATION

Court: United States Court of Appeals for the Federal Circuit Filed: 2026-06-18 The Federal Circuit reversed the district court’s supplemental partial judgment granting IPR estoppel under 35 U.S.C. § 315(e)(2) against Valve Corporation, holding that the district court relied on insufficient evidence to estop one invalidity ground and failed to adequately account for hindsight bias in estopping another. The court applied the “skilled searcher” standard, which requires a patentee asserting estoppel to prove by a preponderance of the evidence that an invalidity ground could have been reasonably raised during inter partes review (IPR) because a skilled searcher conducting a diligent search would have been expected to discover it. Regarding the “Kotkin” ground, the court found the district court erred by concluding a reference was discoverable based solely on classification searches that returned 26,333 results without evidence of further narrowing or manual review; mere accessibility via classification codes is insufficient when the search yields an unreviewable volume of references. Regarding the “Willner-Koji-Raymond” ground, the court held that the district court erred in relying on post-petition search evidence from Cardinal IP because it was tainted by hindsight bias. The court determined that the search methodology relied on forward-and-backward citation searches without date restrictions and a supplemental search conducted only after other references were found, rendering the evidence irrelevant to what would have been discovered at the time of Valve’s IPR petition. The practical consequence is that the case is remanded for further proceedings where the district court must consider the invalidity of U.S. Patent No. 8,641,525 based on the previously estopped grounds (Kotkin and Willner-Koji-Raymond), as the evidentiary basis for estoppel has been vacated. Do It For The Case Law is a news reporting service. Nothing in this episode constitutes legal advice.