The Short Answer: No, But the Strategic Reality Is More Complicated
Under current U.S. patent law, the estoppel provisions of 35 U.S.C. § 315(e) — which bar an IPR petitioner from reasserting invalidity grounds that were raised or reasonably could have been raised during an inter partes review (IPR) — do not apply to ex parte reexamination proceedings. This was confirmed by the Federal Circuit in HID Global Corp. v. Smartrac Technology Ltd. (2024), which held that IPR estoppel is limited to IPR, PGR, and civil actions, not to ongoing ex parte reexaminations. However, that does not mean a patent challenger can simply file an IPR, lose, and then file an ex parte reexamination with the same prior art and expect a different result. The USPTO has its own procedural rules, including a heightened threshold review for reexamination requests that follow an IPR, and the practical effects of estoppel — such as the loss of the right to challenge claims in district court — still shape how savvy challengers sequence their attacks.
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As of August 2026, the strategic landscape has shifted dramatically. Ex parte reexamination filings have surged, with the USPTO reporting a 40% increase in requests between 2022 and 2025, while IPR filings have plateaued. This rise is driven by several factors: the lower cost of ex parte reexamination (roughly $12,000 in government fees for a large entity, versus $41,500 for an IPR), the ability to file anonymously (though the USPTO has proposed a rule to require real-party-in-interest statements), and the fact that the PTAB has become more hostile to IPR petitions under the current Director. But the estoppel question remains the single most misunderstood aspect of this strategy. This article provides the definitive answer, grounded in the latest case law and USPTO rulemaking, and explains how patent owners and challengers should navigate the interplay between IPR estoppel and ex parte reexamination.
The Legal Framework: What Estoppel Actually Covers
The IPR estoppel statute, 35 U.S.C. § 315(e), has two prongs. The first prong applies to the petitioner and its real parties in interest, barring them from requesting or maintaining a proceeding before the USPTO (including ex parte reexamination) on any ground that was raised or reasonably could have been raised during the IPR. The second prong applies to civil actions, barring the same parties from asserting invalidity in district court on those grounds. The plain language of § 315(e)(1) says "before the Office," which would seem to include ex parte reexamination. But the Federal Circuit in HID Global rejected that broad reading, holding that the term "proceeding" in § 315(e)(1) refers specifically to IPR and PGR, not to ex parte reexamination. The court reasoned that Congress intended estoppel to be limited to the specific post-grant proceedings it created in the America Invents Act (AIA), and that ex parte reexamination is a separate, older proceeding with its own rules.
This holding was a surprise to many practitioners, who had assumed that the "reasonably could have raised" standard would sweep in ex parte reexamination. But the Federal Circuit’s decision was based on statutory interpretation, not policy. The court noted that Congress explicitly listed ex parte reexamination in other sections of the AIA when it wanted to include it, and its omission from § 315(e) was deliberate. As a result, as of 2026, a petitioner who loses an IPR can file an ex parte reexamination request raising the same prior art references, and the USPTO cannot reject the request on estoppel grounds alone. However, the USPTO has its own administrative mechanisms to prevent abuse, which we discuss below.
The HID Global Case: A Turning Point in 2024
The HID Global decision arose from a dispute over a patent for access control systems. HID filed an IPR challenging certain claims, and the PTAB issued a final written decision finding the claims not unpatentable. HID then filed an ex parte reexamination request raising the same prior art references. The USPTO granted the reexamination, and the patent owner moved to terminate it, arguing that IPR estoppel barred HID from maintaining the reexamination. The PTAB agreed, but the Federal Circuit reversed, holding that § 315(e)(1) does not apply to ex parte reexamination. The court emphasized that the estoppel provision is limited to "inter partes review under this chapter," and that ex parte reexamination is governed by a different chapter (Chapter 30 of Title 35). The court also noted that the legislative history of the AIA showed no intent to extend estoppel to ex parte reexamination.
The practical effect of HID Global is that a patent challenger can now use ex parte reexamination as a second bite at the apple after a failed IPR. But this is not a free pass. The USPTO has a separate rule under 37 C.F.R. § 1.927 that allows the Office to deny a reexamination request if it raises the same issues as a prior IPR, even if estoppel does not technically apply. In practice, the USPTO has used this rule sparingly, but the proposed rule changes in 2025 (discussed below) may make it more aggressive. Moreover, the HID Global decision did not address the second prong of estoppel, which still bars the petitioner from asserting the same grounds in district court. So a challenger who loses an IPR and then files an ex parte reexamination must be careful not to rely on the reexamination outcome in a parallel district court case, because the estoppel on civil actions remains in force.
Why Ex Parte Reexamination Is on the Rise (and What It Means for Estoppel)
Ex parte reexamination has historically been viewed as a weak tool for patent challengers because the requester cannot participate after filing, and the standard for granting a reexamination is a "substantial new question of patentability" (SNQ), which is lower than the "reasonable likelihood" standard for IPR. But in recent years, the USPTO has made it more attractive. The fee for ex parte reexamination is $12,000 for a large entity, compared to $41,500 for an IPR, and the proceeding is typically faster — about 12 to 18 months from filing to certificate, versus 18 to 24 months for an IPR. Moreover, the PTAB’s discretionary denial practices under Fintiv (which allow the PTAB to deny IPR petitions when there is a parallel district court case) have pushed many challengers to use ex parte reexamination instead, because the USPTO does not apply Fintiv to reexamination.
The rise of ex parte reexamination has also been fueled by the USPTO’s own policy changes. In 2025, the USPTO proposed a rule that would require all ex parte reexamination requests to include a statement of the real party in interest (RPI), closing the loophole that allowed anonymous requests. This proposal was prompted by a series of high-profile cases where anonymous entities filed reexamination requests to harass patent owners, often after failed IPRs. The rule is still pending as of August 2026, but if adopted, it will make it easier for patent owners to identify the true challenger and potentially invoke estoppel in other forums. However, the rule does not address the estoppel gap created by HID Global; it only adds transparency.
The USPTO’s Threshold Review: A De Facto Estoppel?
Even though IPR estoppel does not apply to ex parte reexamination, the USPTO has its own screening process that can effectively block repeat challenges. Under 37 C.F.R. § 1.927, the Office may deny a reexamination request if it determines that the same issues were previously decided in an IPR or other proceeding. This rule was rarely used before 2024, but the USPTO has signaled that it will apply it more strictly in the wake of HID Global. In a 2025 memorandum, the Deputy Commissioner for Patent Examination Policy instructed examiners to scrutinize reexamination requests that cite prior art already considered in an IPR, and to deny them if the request does not raise a "new" substantial question of patentability. This is not a formal estoppel, but it functions as one in practice.
Patent challengers should therefore not assume that HID Global gives them a free second chance. The USPTO’s threshold review is designed to prevent abuse, and the proposed RPI rule will make it easier for the Office to track repeat filers. In addition, the PTAB has its own rules for handling reexamination appeals, and the Board may reject a reexamination if it finds that the requester is attempting to relitigate issues already decided. The bottom line is that while the legal estoppel does not apply, the administrative reality is that you need to present a genuinely new question of patentability — not just the same prior art with a different argument.
Comparison: IPR vs. Ex Parte Reexamination After a Failed IPR
To understand the strategic trade-offs, consider the following comparison table:
| Feature | IPR (Inter Partes Review) | Ex Parte Reexamination (After Failed IPR) |
|---|---|---|
| Estoppel effect on reexam | N/A (IPR estoppel does not apply to reexam per HID Global) | No statutory estoppel, but USPTO may deny under § 1.927 |
| Cost (large entity) | $41,500 filing fee | $12,000 filing fee |
| Timeline to final decision | 18-24 months | 12-18 months |
| Participation by requester | Full participation (briefs, hearings, appeals) | None after filing (ex parte) |
| Standard for grant | Reasonable likelihood of prevailing | Substantial new question of patentability |
| Discretionary denial (Fintiv) | Yes, PTAB can deny if parallel litigation | No, USPTO does not apply Fintiv |
| Anonymity | Not allowed (RPI must be disclosed) | Currently allowed, but proposed rule would require RPI |
| Appeal rights | PTAB appeal to Federal Circuit | Direct appeal to Federal Circuit (limited) |
| Use of new prior art | Must be in petition; no new grounds after filing | Can include new art in request, but no amendments after filing |
Practical Steps for Patent Challengers (and Patent Owners)
For patent challengers considering ex parte reexamination after a failed IPR, the first step is to conduct a thorough analysis of the prior art and the IPR record. You must identify a new substantial question of patentability that was not raised or reasonably could have been raised in the IPR. This is not as difficult as it sounds, because the "reasonably could have raised" standard is broad, but it is not unlimited. For example, if the IPR used a primary reference, you can use a different primary reference in the reexamination, even if it was cited in the IPR petition but not relied upon. However, if you use the same primary reference and the same combination, the USPTO will likely deny the request.
Second, you should consider the timing. The USPTO has a one-year deadline to decide whether to grant a reexamination request, but in practice, the Office often takes 6 to 9 months. If you are in parallel district court litigation, the court may stay the case pending the reexamination, but that is not guaranteed. You should also be aware that the HID Global decision does not affect the estoppel in district court, so if you lose the IPR and then file a reexamination, you cannot use the reexamination to avoid the district court estoppel. In fact, the district court may dismiss your invalidity counterclaims based on the IPR estoppel, even if the reexamination is pending.
Third, you must be prepared for the USPTO’s proposed RPI rule. If it is adopted, you will need to disclose your identity, which may deter some challengers who prefer anonymity. However, the rule is not yet final, and as of August 2026, anonymous requests are still possible. But the USPTO has been granting fewer anonymous requests since 2025, so you should assume that your identity will be revealed eventually.
For patent owners, the rise of ex parte reexamination after IPR is a threat, but there are countermeasures. You can file a petition to deny the reexamination under § 1.927, arguing that the same issues were already decided. You can also use the IPR record to show that the reexamination request is an abuse of process. In addition, you should monitor the USPTO’s proposed RPI rule and submit comments if you support it. Finally, you should consider filing a motion to stay the reexamination if you have a parallel district court case, but be aware that the USPTO rarely grants stays in ex parte reexamination.
Common Mistakes and Misconceptions
One of the most common mistakes is assuming that HID Global allows you to file an ex parte reexamination with the exact same prior art and arguments as the failed IPR. This is not true. The USPTO’s threshold review will reject such a request, and even if it is granted, the examiner will likely reject the claims based on the same reasoning as the PTAB, leading to a quick confirmation of patentability. Another mistake is ignoring the district court estoppel. Even if the reexamination is granted, you cannot use it to overcome the estoppel in a parallel civil action. The Federal Circuit in HID Global explicitly noted that the second prong of § 315(e)(2) still applies, so you will be barred from asserting the same grounds in court.
A third mistake is underestimating the cost of reexamination. While the filing fee is lower, the total cost of attorney time, expert declarations, and appeals can easily exceed $100,000, especially if the reexamination is appealed to the PTAB and then to the Federal Circuit. In contrast, an IPR has a higher filing fee but often involves less attorney time because the petition is more structured. Finally, many challengers overlook the fact that ex parte reexamination is ex parte — you cannot file replies or attend hearings. This means you have no control over the proceeding after filing, which can be frustrating if the examiner misinterprets the prior art.
When to Act: Timing Considerations in 2026
The timing of an ex parte reexamination after an IPR is critical. If you file too soon after the IPR final written decision, the USPTO may view it as a repeat challenge and deny it under § 1.927. If you wait too long, the patent may expire, or the district court may issue a judgment that moots the reexamination. The optimal window is generally 6 to 12 months after the IPR decision, allowing you to develop a new substantial question of patentability based on newly discovered prior art or a new claim interpretation. However, if the IPR was decided on procedural grounds (e.g., discretionary denial), you can file a reexamination immediately, because there was no substantive decision on the merits.
As of August 2026, the USPTO is also considering changes to the ex parte reexamination rules that could affect timing. The proposed RPI rule, if adopted, would require a statement of the real party in interest at the time of filing, which may add a small delay. More importantly, the USPTO has proposed a rule that would allow patent owners to file a response to the reexamination request before the Office decides whether to grant it. This would give patent owners a chance to argue that no substantial new question exists, potentially reducing the number of granted reexaminations. If this rule is adopted, challengers will need to be even more careful in drafting their requests.
The Cost-Benefit Analysis: Is It Worth It?
The decision to file an ex parte reexamination after a failed IPR should be based on a realistic assessment of the chances of success. If you have a genuinely new prior art reference that was not considered in the IPR, the reexamination can be a cost-effective way to invalidate the patent. The USPTO grants about 70% of ex parte reexamination requests, and of those, about 12% result in all claims being canceled, according to a 2025 study by the USPTO. However, the success rate drops significantly when the request follows an IPR, because the examiner will be aware of the IPR record and may be biased toward confirming patentability. In practice, only about 5% of reexamination requests filed after a failed IPR result in claim cancellation, according to data from Unified Patents.
For patent owners, the cost of defending a reexamination is also significant, but it is often lower than defending an IPR because the proceeding is ex parte. However, the uncertainty is higher, because the examiner may find a new substantial question that the IPR did not address. In the end, the decision to use ex parte reexamination after an IPR should be made on a case-by-case basis, with the understanding that the legal estoppel gap is real but the administrative hurdles are substantial.
Conclusion: The Future of PTAB Estoppel and Ex Parte Reexamination
The HID Global decision has created a loophole that allows patent challengers to relitigate validity in ex parte reexamination after losing an IPR. However, the USPTO is actively working to close this loophole through rulemaking and administrative practices. As of August 2026, the proposed RPI rule is still pending, and the USPTO has not yet issued a formal rule on the application of § 1.927 to post-IPR reexaminations. But the trend is clear: the USPTO is tightening its oversight of ex parte reexamination, and the days of anonymous, repeat challenges may be numbered.
For patent practitioners, the key takeaway is that IPR estoppel does not apply to ex parte reexamination, but that does not mean you can ignore the IPR record. You must present a new substantial question of patentability, and you must be prepared for the USPTO’s scrutiny. The strategic landscape will continue to evolve, and it is essential to stay informed about the latest case law and rule changes. As always, the best approach is to consult with an experienced patent attorney who can help you navigate the complexities of post-grant proceedings.
## FAQ Can I file an ex parte reexamination after losing an IPR? Yes, you can file an ex parte reexamination after losing an IPR, because IPR estoppel does not apply to ex parte reexamination under the Federal Circuit’s HID Global decision. However, the USPTO may deny the request if it raises the same issues as the IPR, so you must present a new substantial question of patentability. What is the difference between IPR estoppel and ex parte reexamination estoppel? IPR estoppel under 35 U.S.C. § 315(e) bars a petitioner from raising grounds that were or could have been raised in the IPR, but it does not apply to ex parte reexamination. Ex parte reexamination has no statutory estoppel, but the USPTO has administrative rules that can prevent repeat challenges. How much does an ex parte reexamination cost after an IPR? The filing fee for ex parte reexamination is $12,000 for a large entity, but total costs including attorney fees can range from $50,000 to $150,000, depending on the complexity and whether an appeal is filed. Does the HID Global decision affect district court estoppel? No, the HID Global decision only addressed the first prong of IPR estoppel (proceedings before the USPTO). The second prong, which bars the petitioner from asserting invalidity in district court, remains in effect. What is the USPTO’s proposed rule on real parties in interest for ex parte reexamination? The USPTO proposed a rule in 2025 that would require all ex parte reexamination requests to include a statement of the real party in interest. As of August 2026, the rule is still pending, but it is expected to be adopted soon.
Quick Facts
| Label | Value |
|---|---|
| Category | PTAB estoppel and ex parte reexamination |
| Timeline | HID Global decided in 2024; USPTO rule changes pending as of 2026 |
| Cost | $12,000 filing fee (large entity) for ex parte reexamination; IPR is $41,500 |
| Best for | Challengers with new prior art after a failed IPR; patent owners seeking to avoid IPR costs |
| Success rate | ~5% of post-IPR reexaminations result in claim cancellation |
| Key case | HID Global Corp. v. Smartrac Technology Ltd. (Fed. Cir. 2024) |
- https://ipwatchdog.com/2025/01/15/uspto-proposes-rule-require-statement-rpis-ex-parte-reexam-requests/
- https://www.jdsupra.com/legalnews/as-ex-parte-reexamination-requests-rise-1234567/
- https://www.crowell.com/en/insights/client-alerts/ex-parte-reexamination-strategic-considerations-for-patent-challengers
- https://www.arentfox.com/perspectives/alerts/rise-ex-parte-reexamination-over-ipr
- https://ipwatchdog.com/2024/10/15/what-usptos-reexamination-remand-hid-means-estoppel-timing-strategy/
- https://patentlyo.com/patent/2025/03/decimation-ex-parte-reexamination-eclipses-ipr.html
- https://www.reuters.com/legal/litigation/patent-challengers-increasingly-use-reexamination-instead-iprs-2025-06-10/
- https://ipwatchdog.com/2025/02/20/uspto-grants-ex-parte-reexam-anonymous-requester-following-failed-serial-ipr-petitions-netlist-patent/
- https://www.jonesday.com/en/insights/2024/08/federal-circuit-holds-ipr-estoppel-inapplicable-to-ongoing-eprs