Ex parte Reexamination: Strategic Considerations for Patent Challengers in Light of Recent PTAB Policy Changes

Ex parte reexamination is seeing a resurgence in popularity as a cost-effective means to challenge a patent’s validity and should be part of your patent strategy. An ex parte reexamination is a proceeding in which any party — including a patent owner or an anonymous third party — may submit prior art to request that the United States Patent and Trademark Office (USPTO) reassess an issued patent's validity. Once overshadowed by the introduction of inter partes review (IPR) and post-grant review (PGR) following the enactment of the America Invents Act in 2012, ex parte reexamination is now experiencing a significant resurgence as a strategic alternative to both proceedings. This client alert explains what is driving ex parte reexamination’s resurgence and what it means for your patent strategy.

The Shifting Patent Challenge Landscape

Since early 2025, pursuing IPR and PGR petitions has become significantly challenging. A series of USPTO policy changes — beginning with the rescission of the Sotera stipulation safe harbor in February 2025 and culminating in the introduction of a new bifurcated review process that elevated discretionary considerations above the merits — has fundamentally altered the institution landscape. Discretionary denials, which historically accounted for only 15% of all institution denials, now represent about 60%. Faced with this new reality, patent challengers have increasingly looked to ex parte reexamination as a more accessible alternative.

Pros and Cons of Ex Parte Reexamination: Patent Challengers’ Perspective

Ex parte reexaminations were historically a less popular venue for challenging a patent’s validity than IPR proceedings for two primary reasons. First, ex parte reexaminations afford the third-party requester only limited participation. After filing the initial request, the requester has little further involvement in the proceeding except in limited circumstances, as the proceeding is conducted primarily between the patent owner and the USPTO. Second, ex parte reexaminations allow patent owners to freely submit amendments in a manner similar to ordinary patent prosecution, unlike IPR proceedings where a patent owner’s ability to amend claims is severely limited and amendments are rarely granted in practice. As a result, ex parte reexaminations carry the risk that the patent owner may successfully amend around the prior art, potentially leaving the challenger in a worse position than before the proceeding was initiated.

Despite these limitations, ex parte reexamination offers several distinct advantages from a patent challenger’s perspective.

1. High Institution Rate

The USPTO institutes over 90% of ex parte reexamination requests upon a showing of a substantial new question of patentability (SNQ) under 37 C.F.R. § 1.510(b)(1). This standard of proof is a lower bar than the reasonable likelihood of prevailing standard required for IPR institution. This distinction is more meaningful under the current environment, particularly for older patents, where the PTAB has increasingly denied IPR petitions on discretionary grounds based on the patentee’s “settled expectation” of validity.

2. Anonymous Option

Unlike an IPR where the petitioner must identify all real parties in interest and privies, ex parte reexamination may be filed anonymously. This allows challengers to initiate validity proceedings without placing themselves on the patent owner’s radar for potential infringement claims.

3. Timing Flexibility

While IPR petitions must be filed within one year of service of a district court complaint under 35 U.S.C. § 315(b), ex parte reexamination carries no such time bar and may be filed at any point during the life of the patent, including after litigation has already commenced and the IPR deadline has passed.

4. No Statutory Estoppel 

An ex parte reexamination requester is not barred from raising the same prior art arguments in subsequent district court litigation. By contrast, in an IPR proceeding, once a final written decision has been issued, the petitioner is barred from asserting in subsequent district court litigation any ground of invalidity that it raised or reasonably could have raised during the IPR. 35 U.S.C. § 315(e)(2).

5. Cost-Effectiveness

Ex parte reexamination proceedings are generally less expensive than IPR proceedings, given the more limited scope of the requester’s involvement. The Streamlined Reexamination Request (SRR) option offers a further reduced USPTO filing fee, though there is a strict 40-page limit. See MPEP § 2214, subsection II.

6. Serial Requests

The third-party requester receives copies of the official communications during the ex parte reexamination proceeding. Thus, the requester can monitor the proceedings and may file additional requests for ex parte reexamination of the same patent with additional prior art and arguments that oppose the patent owner’s arguments and amendments filed during initial reexamination. If timely filed and raising a substantial new question of patentability (SNQ), the USPTO has discretion to institute a new reexamination proceeding and consolidate it with the ongoing reexamination. In this manner, albeit increasing the costs with each subsequent request, a third-party requester has the ability to intervene during an ex parte reexamination.

Conclusion

As IPR and PGR proceedings have become increasingly difficult to pursue following the 2025 PTAB policy changes, ex parte reexamination has re-emerged as a critical and often preferable tool for challenging patent validity. While its limited participation rights and the patent owner’s broad amendment latitude remain meaningful drawbacks, high institution rates, timing flexibility, anonymous filing, no statutory estoppel, and lower cost make ex parte reexamination a compelling strategic option. Companies and counsel should evaluate whether ex parte reexamination, alone or in combination with district court invalidity defenses, best serves their objectives.