Tune In: Understanding Google v. Sonos and its Patent Prosecution Implications

The U.S. Court of Appeals for the Federal Circuit issued its long-awaited decision in Google LLC v. Sonos, Inc. on August 28, 2025,  providing guidance on the doctrine of prosecution laches. As the first Federal Circuit decision on prosecution laches for a patent issued after 1995—when patent terms changed from 17-years-from issuance to 20-years-from filing—some suspected the Federal Circuit might definitively end the prosecution laches doctrine. Although prosecution laches remains a valid equitable defense, the Federal Circuit placed significant limitations on its applicability.

Prosecution laches developed as a judicially-created doctrine intended to prevent egregious delays in prosecution at a time when prosecution could, in theory, extend indefinitely. To assert prosecution laches as a defense, an accused infringer must prove: (1) “unreasonable and unexplained delay in prosecution that constitutes an egregious misuse of the statutory patent system under the totality of the circumstances” and (2) “prejudice attributable to the delay.” Cancer Rsch. Tech. Ltd. v. Barr Lab’ys, Inc., 625 F.3d 724, 728-29 (Fed. Cir. 2010) (internal quotation marks and citation omitted). Much of the case law up to this point has focused on the “unreasonable and unexplained delay” part of the test. But the Federal Circuit’s decision instead focused on the question of “prejudice.” Google, 2025 WL 2473258, at *6. The court found that an accused infringer cannot claim to be prejudiced by prosecution delays if the relied-upon subject matter supporting the asserted claims was published before the accused infringer began its work and investments in the accused technology. While the non-precedential decision is sweeping and blunt in the context of the specific facts of the case, it leaves several questions as to which circumstances would give rise to a viable prosecution laches defense.

Publication and Prejudice

The Federal Circuit’s decision hinges on the fact that Google’s investment in the accused technology allegedly began sometime in 2014 or 2015, after the 2013 publication date of the earliest patent application in the asserted patent’s family. Id. at *7. Although the asserted claims were actually filed after Google’s alleged intervening rights, the Federal Circuit determined that Google could not be prejudiced by the later continuation patents because it knew about the patent family and what subject matter might be claimed in the future. Id.

The court’s non-precedential decision, however, does not hold that prosecution delays can never be “prejudicial.” Questions remain about the circumstances that would give rise to a successful prosecution laches defense. For instance, tying the prejudice element of prosecution laches to publication suggests that if Google had begun investment in the accused infringing product before the publication date of the relied-upon disclosure, the prejudice element would have been satisfied. If that is the case, a patent applicant might significantly increase the risk of prosecution laches by delaying publication of an application, such as with a nonpublication request, then filing a continuation.

Further, the Federal Circuit’s focus on when Google received proper notice of the relied-upon disclosure makes continuations an outlier compared to other aspects of patent law. In this vein, the Federal Circuit notably cites to Eli Lilly & Co. v. Hospira, Inc., 933 F.3d 1320, 1334 (Fed. Cir. 2019) stating that “subject matter disclosed but not claimed is generally dedicated to the public.” Thus, unclaimed embodiments in the specification are generally considered to be in the public domain, unless later claimed in a continuing application with a valid priority claim or another application that can exclude the relied-upon disclosure as prior art.

Timing of publication aside, the court’s decision is, at least in part, based on Google’s sparse evidence demonstrating “prejudice.” Google, 2025 WL 2473258, at *6. The court’s decision does not hold as a matter of law that publication of later-patented subject matter nullifies any claim of prejudice from investment activities that happen after its publication. For instance, the court’s decision suggests that prejudice might be shown by evidence that the accused party was “caught unawares” that the patentee “may have already invented” the accused technology, or that a “reasonable factfinder could conclude that the specification… does not reasonably disclose” the patented technology. Id. at *6-7. Indeed, in some scenarios, an accused infringer may have justifiable reasons to believe that the later-patented claims could not be pursued.

For instance, an application that goes abandoned for an extended period of time (several years) may give the accused party a reasonable expectation that no additional patents would issue from those disclosed embodiments.

Furthermore, a court could potentially find it prejudicial for an applicant to correct defects in the priority claim of a continuing application after the application has published. For instance, an Applicant’s investment activities may include engaging legal counsel to provide freedom-to-operate (FTO) opinions, and their continued work on a technology would likely be based on the FTO guidance. For published applications that have not yet issued, FTO guidance sometimes forecasts what claim scope might be obtained based on available prior art. If the priority date for the published application changes later due to the applicant’s delay in correcting the priority claim, the Applicant’s investment activities, including its legal due diligence, would have been in vain and thus might give rise to facts showing prejudice.

Additionally, a late correction to the priority claim could be accompanied by an incorporation of subject matter from the earlier patent’s disclosure. In that case, although all of the resulting subject matter was technically published before it was properly incorporated into the later application, its incorporation may allow the applicant to get claims of a scope that the accused party could not have expected at the time of its investment activities. This type of unforeseeable claim scope could be exacerbated for applications that have a complex priority chain to applications having non-overlapping disclosures.

Intervening Rights

In analyzing the prejudice element, the Federal Circuit relied heavily on “evidence of intervening rights.” Id. at *6. The Federal Circuit’s focus on “intervening rights” should raise eyebrows for patent practitioners. The concept of “intervening rights” arises in patent practice often in the context of post-grant claim amendments, such as for amendments during reissue, reexamination, and patent trials. Unlike with continuation applications, patent owners are statutorily prohibited from seeking damages for broadening claims in post-grant applications if the accused infringer can prove intervening rights because the accused infringer does not have proper notice of the broadened scope of the claims. For example, accused infringers have an affirmative defense against bad faith claim amendments under 35 U.S.C. § 252. However, courts have broad discretion to determine when § 252 applies, especially for infringing activity occurring after the claim amendments are filed. Prosecution laches could make the effect of—and case for—validity of post-grant claim amendments weaker in situations where § 252 does not apply.

Takeaways

We know one thing for sure: that prosecution laches still applies in some cases, even for post-1995 patents. Post-Google, practitioners may mitigate risk of a prosecution laches challenge for a later continuation if their first-filed publication signals a likelihood of pursuing additional claims of different scope in the future. That means including strong support in the specification for additional embodiments or different combinations of features that are not claimed initially but will likely be claimed in the future. For example, patent drafters can make clear the intent to prosecute specific embodiments later in prosecution by including additional claims (beyond the original 20 claims) in the detailed description, a provisional application, or Patent Cooperation Treaty (PCT) application, which can later be used to support claims in future continuation applications. Drafters should also keep in mind how dependent claims can act as a springboard for future continuation claim sets. Using these strategies, patent drafters can reduce the risk of future continuation claims being challenged under prosecution laches while providing flexibility to decide which embodiments in the specification to protect.

Additionally, filing one or more continuations early in the life cycle—even before publication of the original application occurs—can help indicate an intent to file additional continuation applications later. This has the additional benefit of avoiding the steep costs of the USPTO continuation priority fees after 6 and 9 years from earliest filing.

In the post-grant context, practitioners may reduce the risk of a prosecution laches defense by drafting strong claims to reduce the need for modifications after issuance. Additionally, when drafting dependent claims, practitioners should keep in mind accounting for potential issues that could foreseeably arise in future patent trials and reexamination proceedings.

Finally, practitioners should understand that the case law on prosecution laches is likely still evolving, and additional court rulings may be forthcoming.

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Author: alexskopje