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Sonos v. Google: The Return of Prosecution Laches?

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In a recent decision (the Sonos case), the U.S. District Court for the Northern District of California has potentially breathed new life into a dormant doctrine—the doctrine of prosecution laches.[1]

While this doctrine has existed for years, it has rarely been applied, except for its repeated use against the Lemelson Foundation[2] and Gilbert Hyatt.[3]  However, those cases relate to a narrow (albeit numerous) group of patent applications with priority dates claiming the benefit of patents filed before the pre-1995 change in patent law but issued after 1995 – so-called “submarine patents.” This is a significant distinction, as the calculation of patent term changed dramatically in 1995—moving from 17 years from the date of issuance to 20 years from the date of filing.

Outside of that context, prosecution laches has rarely been applied by courts.  Prosecution laches is an equitable affirmative defense and may “‘render a patent unenforceable when it has issued only after an unreasonable and unexplained delay in prosecution that constitutes districtous misuse of the statutory patent system under a totality of the circumstances.’”
[4] In Sonos, the  district court used this doctrine to deny a $32 million dollar jury verdict against Google, declaring the Sonos patent unenforceable due to prosecution laches.

In Sonos, the patented invention involved arranging media players in different rooms using a system that lets users create, save, and activate groups of these players from specific rooms.  Effectively, this allowed users to manage multiple music or video players in a home. Sonos originally filed a provisional application for the invention in 2006.  Sonos obtained a series of U.S. patents between 2008 and 2019 relating to various aspects of the original application.  Each time Sonos issued a patent, a continuation was filed with new claims, and Sonos subsequently prosecuted it.  Continuation practice in the United States of this nature is legal and common.  Many companies file multiple continuations to seek varying levels of claim scope.  Further, it is also true that a patent applicant can draft claims to read on competitors’ products and claim a priority date that precedes them.[5]  Generally speaking, there is nothing wrong, unlawful, or inequitable about any of this.

After the above-noted law change regarding patent terms, most patent attorneys believed that the rationale for prosecution laches was vitiated by the change in patent term.  As the life of each continuation is necessarily tied to the oldest application to which it claims priority, a patentee cannot extend the life of a patent indefinitely, as was the case with pre-1995 continuations (because each patent had a new term beginning with its issuance).

However, in this case, Google argued that the mere fact that so many continuations were filed over such a long period of time was evidence of “unreasonable” behavior.  The district court agreed with those arguments, noting “[t]he essence of this order is that the patents issued after an unreasonable, inexcusable, and prejudicial delay of over thirteen years by the patent holder, Sonos, Inc. Sonos filed the provisional application from which the patents in suit claim priority in 2006, but it did not file the applications for these patents and present the asserted claims for examination until 2019.”

In making this finding, the judge looked at past precedent (all related to pre-1995 filings) and noted that 8, 9, and 10-year delays had previously been found to be “unreasonable.”  Sonos argued that each continuation it had filed had been diligently prosecuted and complied with all USPTO rules and regulations.  The judge rejected that argument, noting “[t]hat Sonos diligently prosecuted patent applications in the interim does not render the delay any less unreasonable and inexcusable. Rather, it renders the delay more unreasonable and inexcusable.  At all relevant times in the more than thirteen years it took for Sonos to present its claims, Sonos had related applications on file.  It would have been a small step for Sonos to amend those applications to claim the invention.”

Separately, the judge could have relied on issues of potential new matter and indefiniteness in making this decision.  However, the district court chose to issue a ruling focusing on prosecution laches, putting into question a standard practice in the U.S. of filing serial continuations, which allows patent applicants to refine their claims over time and adapt to changing circumstances and has long been a common practice in the United States. This practice allows inventors to align their patent claims with the evolving technological landscape.  The ruling's scrutiny of lengthy delays in presenting claims may encourage patent applicants to reevaluate their continuation strategies and consider being more proactive in asserting their claims, thus reducing the risk of prosecution laches claims.  Moreover, the scope of what constitutes an “unreasonable delay” in presenting such claims is now in question.  Indeed, with the Sonos court, delays of 8 years or more in presenting claims would be questioned.   To what extent defendants in patent suits employ these arguments going forward remains to be seen. 

Another interesting component to this case is that Sonos specifically argued that the 1995 patent term change had rendered prosecution laches moot.  “Sonos have spilled much ink in seeking to demonstrate that the affirmative defense of prosecution laches is dead.  It is not. . . . In establishing the defense of prosecution laches, the Supreme Court was less concerned with the nuances of patent term duration and more concerned with manipulating patent monopoly for profit at the expense of public enjoyment.  And that is precisely what this Court is concerned with here.” In sum, the court emphasized that the defense of prosecution laches is primarily concerned with preventing the manipulation of patent monopolies for profit at the expense of public benefit.

The Sonos case is significant for the entire patent system, raising questions about the balance between innovation and competition and encouraging patent holders to act promptly and reasonably. This case highlights the importance of protecting public interests in intellectual property matters and ensuring that patent holders cannot unfairly exploit the system.  While the court emphasized preventing unwarranted monopolies and protecting the integrity of the patent system, this ruling questions the duration of patent prosecution delays and challenges the notion of prosecution laches. The ruling's potential impact on the practice of filing serial continuations and the definition of "unreasonable delay" in patent prosecution may reshape how patent applicants navigate the patent system.  It also reminds us that patent law is not static and must adapt to ensure it continues to serve the public interest in an ever-changing technological landscape.  Though it's not yet clear how far-reaching the effects of this ruling will be, it's a significant step forward in the ongoing discussion about the use of prosecution laches in patent law.  Finally, of course, it remains to be seen whether the district court’s decision will be affirmed or reversed upon the near-certain appeal to the U.S. Court of Appeals for the Federal Circuit.



[1] Sonos, Inc. v. Google LLC, No. C 20-06754 WHA, No. C 21-07559 WHA (N.D. Cal. Oct. 6, 2023.)

[2] Symbol Tech. Inc. v. Lemelson Med., Educ., & Research Found., 422 F.3d 1378, 1385, 76 USPQ2d 1354, 1360 (Fed. Cir. 2005)

[3] Hyatt v. Hirshfeld, 998 F.3d 1347, 2021 USPQ2d 591 (Fed. Cir. 2021)

[4] Cancer Research Tech. Ltd. v. Barr Lab’ys Inc., 625 F.3d 724, 728 (Fed. Cir. 2010)

[5] See Liebel-Flarsheim Co. v. Medrad, Inc., 358 F.3d 898, 909 n.2 (Fed. Cir. 2004)