Ironburg Inventions Ltd. v. Valve Corp., Appeal No. 2024-2088 (Fed. Cir. June 18, 2026)

In its only precedential patent opinion last week, the Federal Circuit for the second time considered estoppel under 35 U.S.C. § 315(e) in the context of infringement claims against videogame controllers provided by Valve Corporation.  Section 315(e) prohibits a petitioner in a completed inter partes review from later asserting any grounds for invalidity “that the petitioner raised or reasonably could have raised during that inter partes review.”  In a previous appeal in this case in 2023 (our write up here), the Federal Circuit held for the first time that the standard to be applied for the “reasonably could have raised” inquiry is whether “a skilled searcher conducting a diligent search reasonably could have been expected to discover” the grounds to be estopped.  In the instant appeal following remand, the Federal Circuit provided further guidance on application of that “skilled searcher” standard, reversing the district court’s conclusion that Valve’s relevant invalidity arguments were estopped.

The case concerns allegations that certain videogame controllers offered by Valve infringe claims of Ironburg’s U.S. Patent No. 8,641,525.  After Ironburg filed suit, Valve petitioned for an IPR in April 2016 that resulted in a final written decision in September 2017.  At issue in the instant appeal were two non-petitioned grounds for invalidity that Valve subsequently raised in district court, specifically (1) anticipation by a prior art reference referred to as “Kotkin,” and (2) obviousness over a combination of references referred to as “Willner,” “Koji,” and “Raymond.”  The district court found that a skilled searcher could reasonably have been expected to discover each of the prior art references in April 2016, such that Valve was estopped from raising them in the litigation.  However, the Federal Circuit found the district court’s determinations in each instance to be either insufficiently supported or infected by hindsight bias.

As to Kotkin, the district court’s determination was based on expert testimony that “classification”-based searches relevant to the subject matter of the ’525 patent would have revealed the reference.  However, the classification searches submitted to support this point had returned over 26,000 results alongside the references at issue, and Ironburg—the party with the burden to show discoverability—did not provide further evidence of how a skilled searcher might have narrowed those results.  While the Federal Circuit declined to hold that manual review of search results was in all instances required to establish reasonable discoverability, it noted that “thousands of sources, not further narrowed in any way, likely cannot be considered discoverable for estoppel purposes under § 315(e)(2).”  Accordingly, the Court held “that something more is required for estoppel when a classification search alone returns an unreviewable number of search results.”  Because there was indisputably nothing “more” provided here, the reviewing panel concluded Ironburg had not met its burden, and reversed the district court’s finding that Valve’s Kotkin-based ground was estopped.

As to the Willner-Koji-Raymond ground, the Court framed its discussion with a reminder that Section 315(e) speaks in terms of “grounds” that could have been raised in IPR, not specific prior art references.  Accordingly, if even one reference comprising an asserted obviousness combination would not have been discovered under the “skilled searcher” test, then that combination is not estopped as grounds for invalidation.  Here, Ironburg’s evidence was built on searches performed in 2023 that included “forward-and-backward citation” queries, and whose results were informed by prior art citations in materials that were not created until after Valve filed its IPR in April 2016.  One of Ironburg’s witnesses also admitted that a second, “supplemental” search was undertaken specifically to locate the Raymond reference.  Because Ironburg’s evidence was in both instances infected by hindsight, the Federal Circuit found it to be “not probative regarding a skilled searcher’s discovery of Kotkin, Koji, or Raymond at the time of Valve’s IPR petition,” and that Ironburg again failed to carry its burden.

Accordingly, the panel reversed the district court’s estoppel findings, and remanded for further consideration of the ’825 patent’s validity in view of Valve’s arguments on the Kotkin and Willner-Koji-Raymond grounds.  Judge Stark entered a concurring opinion to highlight the panel’s precedential holdings, and to argue for a bifurcated standard under which the proponent of estoppel would be required to show both that the relevant prior art reference(s) are reasonably “findable” and, separately, that related grounds for invalidity are reasonably “discoverable.”

The opinion can be found here.

By Jason Wrubleski

This article summarizes aspects of the law and does not constitute legal advice. For legal advice with regard to your situation, you should contact an attorney.