Patenting for Inventors Ep. 181: The Hidden Risk of Keeping a Patent Application Alive Too Long – Prosecution Laches
Keeping a Patent Application Alive Can Come Back to Bite You
Patent prosecution can take years, and usually for good reasons. But when delay becomes extraordinary and unexplained, and competitors invest millions while no enforceable patent exists, courts and the USPTO may step in.
On this episode of Patenting for Inventors, Nolan Heimann partner and registered patent attorney Adam Diament unpacks prosecution laches, an equitable doctrine that can block enforcement of a patent that is otherwise perfectly valid.
Adam explains what "prejudice" really means, why the Federal Circuit's six-year presumption shifts the burden to the applicant, and how the old 17-year patent term gave rise to "submarine patents." He also walks through the Gilbert Hyatt litigation, where the USPTO used prosecution laches to refuse to issue patents, and what the Supreme Court's June 2026 denial of review means for applicants now. Finally, he separates prosecution laches from litigation laches and equitable estoppel, three doctrines that sound alike but apply at very different stages.
For inventors and businesses relying on continuation practice, the takeaway is clear: have a legitimate reason for every step, document your strategy, and assume your prosecution history may be read by a judge years from now. For more on how courts read patents, listen to Ep. 178: Why Patent Examiners and Judges Don't Read Your Patent the Same Way.
Patenting for Inventors Ep. 181:
Podcast Transcript:
Hello, and welcome to the Patenting for Inventors podcast. I'm your host, Adam Diament, a registered patent attorney and partner at the law firm of Nolan Heimann in Los Angeles, California.
Today we are talking about a rarely used but important patent-law doctrine called prosecution laches. The name sounds complicated, so let's start with the basic idea.
Imagine that someone files a patent application. Years pass, and the inventor does all kinds of things, maybe on purpose, maybe not, that delay the granting of the patent. During that time, an entire industry develops. Companies invest millions of dollars, launch products, hire employees, and build their businesses.
Then, many years later, the patent finally issues. The patent owner appears and says: "Surprise. You are infringing my patent. Now pay me."
A court may look at that situation and ask whether it would be unfair to let the patent owner enforce the patent, given that it took so long to issue because of what the inventor did. That is the basic concern behind prosecution laches.
First, let's clarify what "prosecution" means. In patent law, prosecution is not a criminal case. It simply means communicating with the Patent Office to try to obtain a patent. An applicant might file amendments, respond to office actions, appeal rejections, or file continuation applications to pursue different claims.
Those activities are generally legitimate. Patent applicants are allowed to use continuations and other prosecution tools. A long prosecution history does not automatically mean there is a problem.
Prosecution laches is about more than delay alone. It generally requires an extraordinary, unreasonable, and unexplained delay, along with prejudice to others who relied on the absence of an enforceable patent.
"Prejudice" means more than inconvenience. It usually means that other companies made important decisions during the delay, such as investing money, developing products, building factories, or entering markets.
For example, imagine that a company spends ten years developing a product. It raises money, hires employees, sells the product, and builds a customer base. A patent then issues from an old application, and the claims appear to cover the company's product. If the patent owner intentionally waited to see how the industry developed before shaping the claims, the defendant may argue that enforcing the patent would be unfair. That is the kind of fact pattern in which prosecution laches becomes relevant.
The doctrine is difficult to prove. Courts do not apply it every time a patent application takes a long time to issue. Patent prosecution can take years for ordinary reasons. The invention may be technically complicated. The Patent Office may issue multiple rejections. The applicant may pursue different claim strategies. The applicant may file continuations to protect different aspects of the invention. Those facts, by themselves, do not establish prosecution laches.
The question is what the entire prosecution history suggests. Was the applicant genuinely trying to obtain reasonable patent protection? Or does the record look like the applicant was deliberately keeping the application alive while watching competitors and waiting for the industry to reveal what was commercially valuable?
The second situation is much more dangerous.
It is also important to understand why someone might want to delay. Information can be valuable. If an application remains pending, the applicant may be able to observe:
which technologies become commercially successful;
which products competitors launch;
which industry standards become important; and
which businesses enter the market.
An applicant might then try to pursue claims that closely match a competitor's successful product. That may create a serious fairness problem, especially if the delay was intentional and the competitor made substantial investments while no enforceable patent existed.
There is an important Federal Circuit rule to know. When prosecution delay reaches six years or more, the court has said that a presumption may arise that the delay was unreasonable, inexcusable, and prejudicial.
That does not automatically mean the patent owner loses. It means the applicant may need to provide a persuasive explanation for the delay or show that others were not actually harmed. The six-year concept is not a simple deadline saying that every application must issue within six years. It is a warning that a very long delay can shift the practical burden to the applicant.
There is also important historical background. Many of the most famous prosecution-laches cases involve applications filed before June 8, 1995. Before that date, a U.S. patent generally lasted 17 years from the date it issued. That created an opportunity for what became known as a "submarine patent." An applicant could keep an application pending for years and then obtain a patent that remained enforceable for a long period after the industry had already developed.
Modern utility patents generally have a term of 20 years from the earliest effective nonprovisional filing date. That means keeping a modern application pending usually does not create a brand-new 20-year term beginning on the issue date.
But the Federal Circuit has not limited prosecution laches only to older applications. The doctrine can still matter in an unusual modern case if the applicant's conduct and the resulting prejudice make enforcement or issuance inequitable.
Another point that is easy to miss is where prosecution laches can arise. The usual way, which I've talked about, is that it can be raised in litigation after a patent issues. A defendant may argue that the patent should not be enforced because of the applicant's unreasonable delay. But the USPTO has also invoked prosecution laches as a reason to refuse to issue a patent in exceptional circumstances.
That issue is currently associated with the case of Gilbert Hyatt. Hyatt had a large group of patent applications with very long prosecution histories. The Federal Circuit upheld the USPTO's use of prosecution laches in refusing to issue the applications. Hyatt then asked the U.S. Supreme Court to review the case. In June 2026, the Supreme Court denied the petition for certiorari, meaning it declined to hear the case.
In July 2026, Hyatt filed a petition asking the Supreme Court to reconsider that denial. As of this recording, that rehearing request is still pending, but the Supreme Court has not agreed to hear the merits of the case. That means there is currently no Supreme Court decision eliminating or limiting the Federal Circuit's prosecution-laches doctrine. For now, the Federal Circuit's approach remains important.
The Hyatt case also highlights why the doctrine is controversial. Applicants argue that Congress created detailed rules governing patent prosecution. Those rules address filing deadlines, continuations, responses to office actions, appeals, and other steps. The applicants' argument is essentially: "If I complied with the deadlines Congress created, why can a court or the USPTO create an additional judge-made time limit?"
The government and defendants respond that the doctrine is necessary to prevent applicants from using the patent system unfairly. That debate has not been resolved by a Supreme Court merits decision, because the Supreme Court declined to take Hyatt's case.
From the patent owner's perspective, prosecution laches can be a vulnerability during litigation. A defendant may raise it as an equitable defense and argue that the patent should not be enforced because of the applicant's unreasonable delay and the resulting prejudice.
That is different from arguing that the patent is invalid. An invalid patent may fail because, for example, the invention was not new, the claims were obvious, or the application did not adequately describe or enable the invention. A patent affected by prosecution laches may still satisfy the technical requirements for validity, but a court may nevertheless refuse to enforce it because of the applicant's conduct.
From the applicant's perspective, the lesson is not "never file a continuation." Continuations are an important and legitimate part of patent strategy. The lesson is to have a clear reason for continuing prosecution and to maintain a record that explains the strategy.
For example, a continuation may be reasonable because:
the applicant wants claims directed to a different statutory category;
the examiner has indicated that a different claim scope may be allowable;
the applicant wants to protect a commercial embodiment already described in the application; or
the technology has several distinct aspects that deserve separate claim sets.
Those explanations are very different from intentionally waiting to see what competitors build and then trying to draft claims around those products.
A useful practical test is to imagine explaining the prosecution history to a judge who does not know the people involved. Would the history sound like a normal effort to obtain appropriate patent protection? Or would it sound like the applicant was keeping the application alive as a legal ambush? That does not replace legal analysis, but it is a useful warning sign.
Now let's distinguish prosecution laches from ordinary laches in patent litigation.
Prosecution laches concerns conduct before the patent issues. It asks whether the applicant waited too long during the patent-application process and whether that delay caused unfair prejudice.
Litigation laches concerns conduct after the patent issues. It asks whether the patent owner waited too long to sue after learning about the alleged infringement.
These doctrines are related in name but operate in different settings. The Supreme Court has held that ordinary laches generally cannot be used to eliminate damages that fall within the Patent Act's six-year damages period. In simple terms, a patent owner who sues today may generally seek damages for infringement occurring during the preceding six years, subject to other defenses and requirements.
Post-issuance delay can still matter in other ways. For example, it may affect whether a court grants an injunction.
Equitable estoppel may also apply if the patent owner made misleading statements or engaged in conduct that caused the accused company to reasonably believe it would not be sued, and the company relied on that conduct.
So the key distinction is:
prosecution laches concerns delay before the patent issues;
litigation laches concerns delay after the patent issues; and
equitable estoppel concerns misleading conduct and reliance.
To recap, prosecution laches is not a rule that punishes every long patent application. Continuations and amendments are generally legitimate. The risk arises when the prosecution history suggests extraordinary and unexplained delay, claims shaped around later-developed products, and real prejudice to businesses that invested while no enforceable patent existed.
The doctrine can potentially arise both in litigation and before the USPTO. The Federal Circuit's six-year presumption is an important warning sign, and the Supreme Court's denial of review in Hyatt means the Federal Circuit's approach currently remains in place.
The practical lesson is simple: use continuation practice for legitimate patent objectives, document the reasons for your strategy, and remember that prosecution conduct may be examined years later.
That's it for today's episode. If you need help filing a patent application or protecting other intellectual property, give me a call at 424-281-0162.
Until next time, I'm Adam Diament, and keep on inventing!