by Dennis Crouch
The Federal Circuit has now wiped away Judge William Alsup's dramatic post-trial decision in Sonos v. Google. In a nonprecedential opinion, the court reversed the lower court's finding of prosecution laches, reiterating that laches is an equitable defense reserved for rare cases. Google LLC v. Sonos, Inc., No. 2024-1097 (Fed. Cir. Aug. 28, 2025).
Prosecution laches requires both (1) an unreasonable and unexplained delay in patent prosecution and (2) a showing of prejudice to the accused infringer in the form of intervening rights (e.g. evidence that others "invested in, worked on, or used the claimed technology during the period of delay"). Here, Google failed to present evidence that it (or others) changed their position or made investments in reliance on Sonos's delay and so laches could not apply. At times, egregious delay can trigger laches absent a specific showing of harm. Here, however, the panel emphasized that standard continuation practice, even over more than a decade, is not itself an "egregious misuse" of the system sufficient to trigger laches in the absence of specific prejudice. Prior prosecution laches cases all involved pre-1995 patents and decades of delay and this was the first time prosecution laches had been used to render a post-1995 patent unenforceable in a situation where delays in prosecution automatically delayed patent term as well. The court ultimately reversed Judge Alsup's unenforceability ruling and reinstated the jury's $32 million verdict on the Sonos "zone scenes" patents.
Although Sonos won the appeal, the decision does not provide a full green light to the continuation practice found here - particularly where claims covering competitor activity are first added to the patent family long after the original filing and publication dates. The Federal Circuit's analysis focused heavily on the fact that Sonos's 2007 patent application previously published, well before Google's alleged investments began in 2014-2015. This meant Google could not claim prejudice from incorporating into its products a feature that was already publicly disclosed in a pending patent family.