Patent Infringement Defense: Why Validity Challenges May Get Harder

Patent Infringement Defense Is Becoming a Timing Problem

Patent infringement defense has long depended on a basic strategic premise: if a company is sued on a patent that appears weak, it may be able to challenge validity at the Patent Trial and Appeal Board through inter partes review, often in parallel with district court litigation. That premise is now less reliable. The USPTO has proposed rules that would narrow when inter partes review is available, and Bloomberg Law reported on July 3, 2026, that the future of those proposed limits is now uncertain after significant pushback. The agency’s spring regulatory agenda lists the planned PTAB rule update, RIN 0651-AD89, as “undetermined.”

For founders, executives, investors, and litigation teams, the issue is not merely procedural. If PTAB access narrows, or if the uncertainty itself continues, patent infringement defense becomes more front-loaded. Accused infringers may need to evaluate invalidity arguments, district court defenses, estoppel risk, settlement leverage, and alternative Patent Office procedures earlier in the dispute. Patent owners, meanwhile, may see stronger enforcement leverage if repeated or parallel administrative challenges become harder to bring.

The USPTO Proposal Would Narrow the PTAB Door

The proposed rule was published in the Federal Register in October 2025 and is aimed at revising PTAB practice for institution of inter partes review. The USPTO stated that the proposal would focus IPR proceedings on patent claims that have not previously been challenged in litigation, or where prior litigation was resolved at an early stage, with the stated goal of promoting fairness, efficiency, and predictability in patent disputes.

The agency’s own announcement described the proposal in practical terms. It would require an IPR petitioner to stipulate that it will not pursue invalidity challenges under 35 U.S.C. §§ 102 or 103 in other forums. It would also provide that the USPTO will not institute IPR when the USPTO or another forum has already adjudicated patentability or validity of the claims, or when another proceeding is likely to decide patentability or validity first. In effect, the proposal pushes toward a “one-and-done system” or single-challenge framework for validity challenges. The While the proposal would leave room for institution in exceptional circumstances, but the general direction is clear: fewer repeated or parallel validity challenges.

The comment period was later extended to December 2, 2025, confirming that the rulemaking drew enough stakeholder attention to require more time for public input. As of the latest regulatory agenda referenced by Bloomberg Law, however, the final path remains unclear. That uncertainty is itself consequential because litigation strategy depends on predictable sequencing, and patent litigants now must plan around a PTAB system whose access rules may change while a case is already underway.

Why the Change Matters for Patent Infringement Defense

Inter partes review is limited by statute. Under 35 U.S.C. § 311, a petitioner may challenge patent claims only on grounds that could be raised under §§ 102 or 103 and only on the basis of patents or printed publications. Under 35 U.S.C. § 315, an IPR generally cannot be instituted if the petition is filed more than one year after the petitioner, real party in interest, or privy is served with a complaint alleging infringement. These limits already make timing and prior art selection critical.

The proposed rule would add another strategic layer. If a defendant must waive other novelty and obviousness challenges in district court or the ITC to obtain IPR institution, the defendant’s choice becomes more expensive. It is no longer simply a question of whether the PTAB is faster or more technically focused than district court. It becomes a question of whether the defendant can afford to give up parallel invalidity positions before knowing how claim construction, discovery, venue, settlement, or early motions will develop.

That change would make patent infringement defense less forgiving. A defendant that waits too long may lose PTAB access through discretionary denial, litigation progress, or statutory timing. A defendant that files too early may commit to arguments before full discovery reveals better invalidity evidence. A defendant that petitions aggressively may trigger estoppel or stipulation consequences. Therefore, the best defense posture is shifting from “file an IPR if litigation gets serious” to “decide the validity forum before litigation strategy hardens.”

The PTAB Is Already Operating in a More Discretionary Environment

Even without a final rule, PTAB practice has already become more discretionary. Reuters reported in 2025 that the USPTO introduced a new bifurcated process for discretionary denial in AIA trials, separating threshold discretionary denial analysis from the merits review. Under that process, discretionary issues are reviewed before the petition reaches the merits panel, and the Office considers broader policy, efficiency, and fairness concerns at the institution stage.

That matters because a petition can be strong on the prior art and still fail at the institution gate. A petitioner now has to think about timing, parallel litigation, investment by the district court, claim construction positions, real-party-ininterest disclosures, and policy arguments before the PTAB ever evaluates whether the patent claims are likely invalid. In practical terms, the defense team must win the right to be heard before it can win on the merits.

This is also why ex parte reexamination has received more attention, although it should not be treated as a perfect substitute. Reuters reported in March 2026 that patent challengers have increasingly used ex parte reexamination as an alternative to IPR, partly because of changes in PTAB institution practice. However, reexamination gives the requester less participation after institution, lacks the same trial-like adversarial structure, and does not carry the same statutory schedule as IPR.

What Accused Infringers Should Do Before Litigation Controls the Strategy

For accused infringers, the first practical step is to evaluate validity immediately after receiving a demand letter, complaint, or credible assertion. Waiting until the one-year IPR deadline approaches is no longer a safe default because discretionary denial arguments may become stronger as district court activity accumulates. Early assessment should include patents and printed publications, system prior art, on-sale activity, product evidence, inventorship issues, written description, enablement, noninfringement, and claim construction.

The second step is to decide which arguments belong in which forum. IPR can only use patents and printed publications for §§ 102 and 103 challenges, so a defense that depends on product prior art, public use, on-sale activity, or technical evidence outside printed publications may need to remain in district court. That distinction became more important after the Federal Circuit’s 2025 Ingenico decision, which Reuters described as clarifying that IPR estoppel does not extend to system prior art that could not have been raised in an IPR.

The third step is to coordinate positions before they conflict. Claim construction arguments, invalidity charts, PTAB petitions, district court contentions, and settlement communications should be developed as one litigation record. In the current environment, inconsistent positions may not merely weaken credibility. They may also support discretionary denial or complicate later estoppel arguments.

The fourth step is budgetary. A company defending a patent claim should not assume that PTAB review will reduce district court exposure. If IPR becomes unavailable or unattractive, the company may need to fund a fuller district court invalidity case, expert discovery, claim construction, summary judgment, and trial preparation. That should affect reserve planning, settlement authority, insurance review, investor communications, and board reporting.

What Patent Owners Should Do While the Rules Remain Unsettled

For patent owners, the uncertainty creates leverage, but it should be used carefully. A patent owner asserting valuable claims should prepare discretionary denial arguments from the outset, especially where parallel litigation is moving quickly, the patent has already survived prior review, or the accused infringer appears to be using the PTAB as a second track rather than a true alternative.

At the same time, patent owners should not assume that every IPR will be denied. Until a final rule is adopted, petitioners can still file strong challenges, and the PTAB remains an active forum for patentability disputes. A patent owner that overplays the policy environment may miss the more important merits work: defending claim scope, preserving validity positions, preparing expert support, and managing district court strategy in a way that does not undermine Patent Office arguments.

Portfolio management also becomes more important. Patent owners should identify claims that have already been tested in court, survived earlier Patent Office review, or support core licensing positions. Those patents may become more valuable if the USPTO ultimately restricts repeated validity challenges. Conversely, patents with prosecution weaknesses, crowded prior art, or overbroad claim language may remain vulnerable despite a more restrictive PTAB environment.

The Investor and Transaction Diligence Angle

Investors and acquirers should treat this development as more than a litigation update. If patent validity challenges become harder, asserted patents may carry greater enforcement value, while defensive freedom-to-operate risk may increase. In IP-heavy transactions, diligence should ask whether key patents have already been tested, whether they remain exposed to IPR, whether potential competitors hold patents that are difficult to challenge, and whether the target has budgeted for litigation paths where PTAB relief is unavailable.

This is particularly important for companies in software, AI, semiconductors, medical devices, telecommunications, and advanced manufacturing, where patent assertions can materially affect product launch, financing, supply chain leverage, and acquisition value. A narrower PTAB path does not automatically make every patent stronger. However, it may make weak patents more expensive to clear.

Timing: The Decision Window Is Earlier Than Many Companies Think

The best time to evaluate patent infringement defense is before litigation is filed, when the company can still choose among declaratory judgment, noninfringement positioning, design-around strategy, licensing, reexamination, IPR, settlement, or business resolution. Once a complaint is served, the one-year IPR clock under § 315 begins to matter, and district court activity can create practical pressure long before the statutory deadline expires.

Within the first 30 to 60 days after a serious assertion, the company should have a preliminary validity map, prior art search direction, forum strategy, budget range, and settlement posture. Within 90 to 120 days, it should know whether IPR is likely to be pursued, whether district court invalidity defenses should be preserved, and whether alternative Patent Office tools have strategic value. Waiting until late-stage litigation may leave the defense team choosing among diminished options.

The Strategic Point

Patent infringement defense is moving toward earlier decisions, tighter forum coordination, and less tolerance for late validity strategy. The USPTO may finalize the proposed PTAB limits, revise them, withdraw them, or leave practitioners in a prolonged period of discretionary uncertainty. In each scenario, the same operating rule applies: defendants should not wait to evaluate invalidity, and patent owners should not wait to build the record that protects their claims.

FAQ: Patent Infringement Defense and PTAB Validity Challenges