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One Claim Limitation Saved Google's Hotword Patents: Lessons from a PTAB Reversal
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The U.S. Court of Appeals for the Federal Circuit has reversed two PTAB decisions that invalidated Google's voice-activation "hotword" patents. The court ruled that the prior art did not anticipate the claims because it failed to disclose exchanging messages while remaining in a low-power mode. This decision underscores the strict evidentiary standards required to prove anticipation in post-grant reviews and highlights the value of precise claim drafting.
On June 9, 2026, the U.S. Court of Appeals for the Federal Circuit (CAFC) reversed and remanded two Patent Trial and Appeal Board (PTAB) decisions in Google LLC v. Sonos, Inc. (Appeal No. 24-2119). The PTAB had previously held that certain claims of Google’s U.S. Patent Nos. 10,134,398 (the ’398 patent) and 10,593,330 (the ’330 patent) were unpatentable as anticipated or obvious. These patents address the problem of multiple voice-assistant devices triggering simultaneously from a single "hotword" by suppressing the reaction in unintended devices.
Chief Judge Moore, authoring the CAFC opinion, held that the Board’s finding of anticipation by prior art reference U.S. Patent No. 8,719,039 (Rosenberger) lacked substantial evidence. The PTAB had concluded that Rosenberger disclosed a device exchanging weighted signals while in a low-power "listening" mode. However, the CAFC found that column 8 of Rosenberger actually describes embodiments where devices exit the low-power mode to calculate and exchange signals upon detecting a spoken trigger. Because the prior art devices do not exchange messages while in the low-power mode, Rosenberger cannot anticipate the claims. The CAFC remanded the case for the PTAB to consider Sonos's alternative theory regarding reduced power consumption during coordination.
This dispute is part of a broader patent conflict between Google and Sonos. As documented in patent litigation studies, both operating companies and non-practicing entities frequently use the PTAB to resolve licensing-based disputes. In this case, both Sonos and Google filed inter partes reviews (IPRs) against each other's portfolios to gain leverage in their commercial disputes.
The CAFC's decision highlights the strict application of the "substantial evidence" standard of review for PTAB factual findings. While the CAFC is deferential to the Board's factual determinations, it will reverse when the Board misinterprets the plain text of a prior art reference. This case contrasts with other recent CAFC decisions involving Google. For instance, in US Pat. No. 7,679,637 LLC v. Google LLC, the court affirmed the dismissal of an infringement suit because the claims used "result-oriented functional language" without explaining how the results were achieved, violating 35 U.S.C. § 101. Similarly, in Nobots LLC v. Google LLC (decided November 20, 2025), the CAFC reversed a PTAB decision because the Board departed from the ordinary meaning of "acquiring interest data" in its claim construction. These cases emphasize that precise claim language and clear technical disclosures are vital to surviving both eligibility and prior art challenges.
For corporate IP leaders and patent attorneys, particularly those managing portfolios for major technology companies in South Korea and the wider Asian region, this ruling provides several actionable lessons. Korean conglomerates, which frequently act as both patent owners and challengers in the U.S. market, must carefully calibrate their prosecution and litigation strategies based on these shifting evidentiary boundaries.
First, when drafting patent applications, attorneys must explicitly define operational states and transitions. In the '398 and '330 patents, the distinction between exchanging messages "while in" a low-power mode versus "after exiting" that mode was the dispositive factor that saved the patents from anticipation. To replicate this success, practitioners should avoid generic functional descriptions of device states. Instead, they must draft claims that couple functional outcomes with specific structural or logical constraints, such as the precise timing of data transmissions relative to power-state transitions.
Second, from a challenger's perspective—such as a Korean firm seeking to invalidate a competitor's U.S. patent at the PTAB—this decision warns against over-reliance on expert testimony to bridge gaps in the prior art. If the plain text of the prior art reference contradicts the expert's characterization, the CAFC will disregard the Board's reliance on that testimony. Challengers must ensure that every claim limitation is mapped to explicit disclosures in the prior art, rather than relying on inferences about how a prior art device might "reasonably" operate.
In terms of comparative practice, Korean filers should note that the Korean Intellectual Property Office (KIPO) tends to apply a highly restrictive standard to added-matter and amendment scope under Article 47(2) of the Korean Patent Act, meaning that Korean patentees must secure explicit support in the original specification for any state-based limitations they wish to introduce during prosecution. Therefore, a Korean company acting as a patentee must ensure that its U.S. applications contain robust, multi-layered dependent claims that can withstand rigorous prior art comparisons during IPR proceedings.
Actionable Practice Tip: Review your active hardware and software portfolios to identify claims that recite "operating modes" (e.g., low-power, standby, active). Ensure that the specification contains explicit definitions of what constitutes entry into and exit from these modes, and draft dependent claims that restrict the claimed steps to occurring strictly within a single, defined mode.
The case now returns to the PTAB, where the Board must address Sonos's alternative theory regarding whether Rosenberger's reduced power consumption during coordination meets the parties' agreed-upon construction of "low power mode" as "an operating mode or state in which power is conserved." This remand highlights the danger of agreeing to broad claim constructions during IPR proceedings that may inadvertently encompass prior art operations.
In the broader landscape, the USPTO continues to refine its eligibility guidelines, particularly concerning software and artificial intelligence. For instance, on November 4, 2025, the PTAB designated Ex parte Desjardins as a precedential Appeals Review Panel decision, clarifying that AI claims reflecting logical improvements are patent-eligible under § 101. This indicates a shifting administrative environment where technical specificity is rewarded across all sectors of digital technology.
Actionable Practice Tip: While this remand is pending, IP owners should audit their pending U.S. applications to ensure they have not agreed to overly broad claim constructions that could expose their patents to anticipation. If a broad construction has been entered, prosecutors should immediately file continuation applications with narrower, more precise claims that explicitly exclude the operational boundaries of known prior art references.