Ingenico and the Federal Circuit’s Elimination of IPR Estoppel

35 U.S.C. §315(e)(2) provides that a petitioner in an inter partes review (IPR) that reaches a Final Written Decision may not then assert invalidity in a district court litigation on any ground that the petitioner “raised or reasonably could have raised” during that IPR. Congress inserted this provision in order to streamline district court litigations and “ensure that if an inter partes review is instituted while litigation is pending, that review will completely substitute for at least the patents-and-printed-publications portion of the civil litigation.”  157 Cong. Rec. S1360-94 (daily ed. Mar. 8, 2011). Defendants can file an IPR, but the tradeoff is that defendants’ invalidity defenses at trial will not include patents or printed publications unless they can show the patents and printed publications could not have reasonably been raised in the IPR.

Ingenico and Ironburg

Recent U.S. Court of Appeals for the Federal Circuit decisions have gutted 35 U.S.C. §315(e)(2). Last week, in Ingenico Inc. v. IOENGINE, LLC, 2025 WL 1318188 (Fed. Cir. 2025), the Federal Circuit resolved an open issue regarding IPR estoppel in district court, holding that system art is never subject to IPR estoppel under 35 U.S.C. §315(e)(2). But Ingenico went much further and also held that “IPR estoppel does not preclude a petitioner from relying on the same patents and printed publications as evidence in asserting a ground that could not be raised during the IPR, such as that the claimed invention was known or used by others, on sale, or in public use.”

To the court in Ingenico, the “ground” is whether the claim was patented, described in a printed publication, or in public use, on sale, or otherwise available to the public rather than simply the prior art used under 102(a) or 103. The specific prior art references used in a ground, according to the court, “are evidence that support a ground that the claimed invention was patented or described in a printed publication, they are not coextensive with a ground.” According to Ingenico, the same prior art patent might serve as evidence of grounds that the claim was not only patented but also described in a printed publication (patents are published), available to the public (patents are publicly available) in public use, or on sale (if the patent describes the operation of a system in public use or on sale). Each case would be a different ground but using the same prior art patent.

Congress would not likely agree with this expansive reading. The statutory provision on IPR estoppel would be pointless if the same patent used in an IPR could then be re-used in a district court litigation in exactly the same manner by replacing “patented” in the IPR with “known,” “used” or “on sale” in the district court. The same prior art arguments that were raised and lost in the IPR under a lower standard for petitioner could often be re-raised in the district court in the same manner. Under Ingenico’s logic, there is no IPR estoppel for the prior art actually raised in the Petition.

The Federal Circuit has similarly limited the “reasonably could have raised” portion of IPR Estoppel. In Ironburg Inventions Ltd. v. Valve Corporation, 64 F.4^th 1274, 1299 (Fed. Cir. 2023), the Federal Circuit held that “the burden of proving, by a preponderance of the evidence, that a skilled searcher exercising reasonable diligence would have identified an invalidity ground rests on the patent holder, as the party asserting and seeking to benefit from the affirmative defense of IPR estoppel.”  Ironburg similarly stated that “[t]he inquiry into what a skilled and diligent searcher would reasonably have discovered is ultimately concerned with what the searcher of ordinary skill would find through reasonable diligence.”  (emphasis in original).

Ironburg’s holding renders IPR estoppel complicated, subjective and potentially meaningless. First, it is not whether a particular search would have necessarily found the relevant reference. Instead, IPR estoppel attaches if the reference “reasonably could have been raised.” That is, the statute asks whether it is reasonable that a patent or printed publication could have been found. The statute does not require that a hypothetical “reasonable searcher” performing a single search necessarily would have found the reference, only that the reference reasonably could have been identified.

These Decisions Eliminate Congress’s Intended Efficiencies

In reality, there is no objective test that defines what a reasonably diligent search could find. Often, defendants employ multiple different professional searchers, each of whom perform reasonably diligent searches. Each search always returns materially different prior art references. By wading into “what the searcher of ordinary skill would find through reasonable diligence” courts are second guessing searchers and creating hypothetical fact issues courts are not well equipped to resolve.

Second, the “reasonable searcher” standard as elaborated by Ironburg invites judicial waste that eliminates any purported efficiency from IPR estoppel. Courts employing this standard create a trial-within-a-trial that requires briefing, expert testimony and evidence on what a reasonable search means. Parties can spend hundreds of thousands of dollars arguing about a hypothetical, subjective search.

Third, placing the burden of proving IPR estoppel on patent owner is counterintuitive and removes any potential efficiencies that IPR estoppel was meant to provide. The cases cited in Ironburg generally relate to proving that equitable estoppel should apply, where it makes sense that the burden would be on the party raising estoppel. Statutory IPR estoppel exists and attaches as soon as a Final Written Decision is entered. Plaintiffs should not have to prove what the statute has already given them. The only question left is the application of the estoppel to specific prior art.

To illustrate, in a district court litigation where defendant is subject to IPR estoppel, the defendant may be asserting dozens of patents or printed publications in its contentions. For most of these patents and printed publications, there is no real argument that they were either raised or reasonably could have been raised in the corresponding IPR. Perhaps for a handful of references, the defendant has a substantive argument about why the reference could not have been identified. But those arguments are the exception to the rule, and the evidence supporting those arguments generally belongs to defendant. Forcing plaintiffs to prove each patent and printed publication asserted by defendant is estopped because a hypothetical searcher necessarily would have found the reference is contrary to the statute and eliminates any potential efficiencies.

Broader Implications

The impact of cases like Ingenico and Ironburg goes beyond the district court. For example, petitioners in IPRs will often file so-called Sotera stipulations to improve their chances of getting IPRs instituted. These stipulate the defendant will not pursue in the district court any ground that was raised or could have been reasonably raised in the IPR. The PTAB has weighed Sotera stipulations in favor of institution, reasoning that they provide at least some streamlining of the issues at the district court.

This is not necessarily true in practice. Under Ingenico, the same patent used in an IPR that reaches a final written decision can potentially be re-used in exactly the same manner in the district court. Moreover, under Ingenico, all system art is always available in district court. And, under Ironburg, unless the plaintiff initiates motion practice, all other patents and printed publications are also presumed to be available to defendants. Even if the patent owner does move to strike or exclude patents and printed publications under IPR estoppel, the burden is on patent owner to do so.

The “reasonably could have raised” standard can and should be implemented much more straightforwardly. Courts should start from a rebuttable presumption that all relevant patents and printed publications reasonably could have been raised in the IPR. If a prior art patent or publication is analogous art, there is little concern that petitioner could not have reasonably raised the reference. Every USPTO patent is word searchable and indexed on the USPTO website. And printed publications by definition must be publicly accessible. The exceptions to IPR estoppel should be edge cases such as where discovery was necessary to identify the reference, or an unexpected claim construction makes additional art relevant. Any analysis of “reasonably could have raised” should start from the reality that relevant patents and printed publications generally could have been identified in a reasonable search and raised in the IPR. Whether a particular hypothetical search would have necessarily found the specific reference is beside the point.

Time to Revisit

Ingenico and Ironburg effectively eliminate IPR estoppel in most, if not all, cases. The Federal Circuit should revisit these decisions with an eye towards giving statutory IPR estoppel meaning. Consistent with 35 U.S.C. §315(e)(2), there should be a rebuttable presumption after a Final Written Decision that all patents and printed publications are estopped. Further, the burden should be on defendants to prove why it was not reasonable to raise particular patents and printed publications in the IPR.

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