Post-Grant Review

Challenging Patents After Grant

Post-grant review (PGR) is an administrative trial proceeding at the United States Patent and Trademark Office (USPTO) that allows a third party to challenge the validity of a U.S. patent shortly after the patent’s issuance. Conducted by the Patent Trial and Appeal Board (PTAB), a PGR provides a faster, more specialized forum than litigation for resolving patent validity issues. This article explains PGR in clear terms for business owners and non-patent attorneys, covering how it works, who can use it, the time frame and process, and the advantages of PGR over other options.

What Is Post-Grant Review?

A post-grant review (PGR) is a proceeding created by the America Invents Act (AIA) that became available in 2012 to review the validity of a patent after grant. It takes place before the Patent Trial and Appeal Board ("PTAB" - an appeal board within the USPTO) and is essentially a trial on a patent’s validity. Unlike the ex parte reexamination process, which involves a patent examiner only, PGR is an adversarial process between a petitioner (challenger) and the patent owner, overseen by a panel of administrative patent judges. The PGR proceeding allows parties to present evidence and arguments about whether the patent’s claims are unpatentable on various grounds. Importantly, PGR is available only for patents examined under the AIA first-to-file rules: patents with an effective filing date on or after March 16, 2013.

Who Can File a PGR Petition?

Any person other than the patentee may file a petition for post-grant review. In practice, the petitioner is often a business competitor or another party facing the patent. The petition must identify the real party in interest, meaning anyone who would benefit from the challenge. However, there are certain bars and prerequisites:

• No Prior Court Challenge: A PGR cannot be instituted if the petitioner or its privy already filed a civil action challenging the patent’s validity before filing the PGR petition. In other words, you can’t sue in district court claiming a patent is invalid and then turn to the USPTO for a post-grant review of that same patent. A counterclaim of invalidity in an infringement suit doesn’t count as a prior action.
• Simultaneous Court Actions: If the petitioner files a declaratory judgment action challenging validity on the same day or after filing the PGR petition, that court action is automatically stayed while the PGR is pending, barring certain conditions. This can streamline disputes by focusing on the PTAB trial first. However, if the patent owner files an infringement lawsuit within three months of the patent grant, a court can still proceed on a preliminary injunction motion despite a PGR filing. Congress provided this to prevent abuse of PGR to delay early injunctions.
• Multiple Petitions: More than one party can file a PGR against the same patent. The PGR procedures allow consolidation of related proceedings in such cases. The Director of the USPTO may join petitions or enter “any appropriate order regarding the additional matter,” including a stay or consolidation, to efficiently manage multiple proceedings on the same patent. In determining whether to institute a PGR, the Director can also consider whether the same or substantially similar prior art or arguments were presented in an earlier proceeding and may deny a duplicative petition or request on that basis to avoid repetition.

When Can You Request a Post-Grant Review?

Timing is critical. A post-grant review petition must be filed within nine months of the patent’s issuance (grant) or reissue. This is a relatively short window. If a patentee obtains a reissue patent, a PGR can be filed any time prior to nine months from the reissue of the patent as well. However, if the reissue claims are identical or narrower than the original claims and the original patent was already beyond its 9-month window, then PGR is not available for those claims. In practice, this means potential challengers must act quickly after a patent grant, monitoring competitor patents and preparing a petition in the time period before the window closes.

After the 9-month window, PGR is no longer available. Instead, a challenger may resort to an inter partes review (a similar proceeding before the PTAB), which has a later timing window, or other options. But for newly issued patents, PGR is the first and broadest opportunity to challenge validity. Because of this strict timing, companies concerned about a new patent should evaluate whether to file a PGR within the nine-month timeframe. Once this window closes, certain validity challenges can no longer be pursued at the PTAB via PGR, including challenging whether the patent covers statutory subject matter under 35 U.S.C. § 101, and grounds under 35 U.S.C. § 112, including enablement, written description, and definiteness.

Grounds for Challenging Patent Claims in PGR

One major appeal of PGR is the broad range of grounds on which the patent claims can be challenged. In a PGR petition, a challenger may request to cancel one or more claims of the patent as unpatentable on any ground that could be raised as an invalidity defense in court. This includes:

• Prior Art challenges: lack of novelty under 35 U.S.C. §102 or obviousness under 35 U.S.C. §103 based on patents, printed publications, or even evidence of prior public use or sale. In other words, any relevant prior art information presented can be used, not only patents and publications (inter partes review is limited to printed publications).
• Ineligible Subject Matter: challenges under §101, arguing the patent claims non-statutory subject matter, such as an abstract idea or natural phenomenon.
• Lack of Written Description or Enablement: challenges under §112(a) for lack of enablement or written description, or indefiniteness under §112(b), asserting the patent’s specification doesn’t adequately describe or enable the claimed invention, or that the claims are too vague. PGR cannot challenge compliance with the best mode requirement, but that is moot since best mode is not an invalidity defense in court either.

By contrast, IPR is limited to Sections 102 and 103 grounds based on patents or printed publications. Thus, PGR offers the broadest possible grounds for challenging a patent, allowing petitioners to attack potentially weak patents on any theory of unpatentability. This means a petitioner can combine multiple grounds, e.g., argue some claims are anticipated by prior art, others are obvious, and others are invalid for lack of written description, all within one proceeding. The petitioner must explicitly identify each claim challenged and the specific grounds and evidence for each. All claims challenged in the petition will be scrutinized if review is instituted.

PGR Petition and Patent Owner’s Preliminary Response

To initiate a post-grant review, the challenger (petitioner) files a petition at the USPTO. The petition is essentially a detailed request to institute post-grant review, and it must meet strict requirements. By statute, the petition must: (1) pay the required fee; (2) identify all real parties in interest; (3) identify each claim challenged, the grounds for each challenge, and supporting evidence for each ground; and (4) provide any other information the USPTO requires by rule. Supporting evidence typically includes copies of prior patents or publications relied upon, as well as affidavits or declarations from experts or witnesses to support factual assertions. In short, the petitioner must put forth its case upfront with particularity, essentially a mini trial brief with evidence to show why the patent claims are invalid.

Once the petition is filed and served, the patentee gets a chance to respond before any trial is instituted. The patent owner may file a preliminary response, within a three-month time frame set by the USPTO, explaining why no post-grant review should be instituted based on the asserted grounds. This is not the full defense on the merits, but rather reasons the petition fails to meet the threshold or has errors. For example, the patent owner’s preliminary response might argue that the prior art cited is not actually relevant or that the petition’s arguments are legally insufficient. As of recent rule changes, the patent owner can include testimonial evidence (e.g. an expert declaration) with the preliminary response to rebut the petition’s factual assertions. The Board will consider any preliminary response and evidence in deciding on institution, though factual conflicts at this stage may be resolved in favor of the petitioner for purposes of the board's decision.

Importantly, the patentee is not required to file a preliminary response. If the patentee chooses not to respond, or no such response is filed by the deadline, the PTAB will proceed to make an institution decision once the time for the preliminary response expires. The absence of a response won’t stop the process; the petition will be evaluated on its own. If no preliminary response is filed, the decision on whether to institute must be made no later than three months after the response deadline.

Institution Decision and Threshold Standards

After the petition and any preliminary response are in, the PTAB will decide whether to institute post-grant review, i.e. whether the case will proceed to trial. The AIA sets a threshold that the petition must meet for a PGR to be instituted. The USPTO may not authorize PGR unless it determines that, considering the petition’s unrebutted evidence, “it is more likely than not that at least one of the claims challenged in the petition is unpatentable.” In other words, the PTAB needs to see a better than 50/50 chance that the petitioner will win on at least one claim. This “more likely than not” standard is a higher bar than the “reasonable likelihood” standard used for IPR institution, reflecting that PGR allows broader attacks. In addition, PGR has an alternate basis for institution: the threshold can be met if “the petition raises a novel or unsettled legal question that is important to other patents or patent applications.” This means if the case presents an issue of first impression (e.g., an unclear point of law in patentability) with broad impact, the PTAB may institute review even if invalidity is not plainly greater than 50% likely. In practice, most PGR institutions rely on the “more likely than not” unpatentability standard.

The PTAB must decide whether to institute the PGR fairly quickly. By statute, within three months after the patentee’s preliminary response is received or after the response period if no response is filed, the USPTO will issue a written decision either instituting the review on some or all challenged claims or denying the petition entirely. If the PTAB institutes post-grant review, the review is officially begun on the instituted claims and all challenged claims should be addressed in the final decision. If the threshold isn’t met, the petition is denied and the process ends without a trial. The decision on whether to institute is by law final and nonappealable, meaning the petitioner cannot challenge a denial in court, nor can the patentee appeal a decision to institute.

Sometimes multiple petitions or other proceedings involve the same patent. The USPTO has discretion to avoid duplicative efforts. For example, if a substantially similar validity challenge was already made in the USPTO (perhaps in a prior PGR/IPR petition or a reexamination), the Director may refuse to institute the PGR, noting that the same prior art or arguments were previously presented. If another USPTO proceeding, such as a matter involving a reissue or ex parte reexamination of the patent is ongoing, the Director can manage the situation by entering an appropriate order to stay, transfer, or consolidate the proceedings so they don’t conflict. These provisions help prevent multiple bites at the apple and inconsistent outcomes.

The Post-Grant Review Trial Process

If a post-grant review is instituted, the review enters a trial phase before the PTAB. This phase operates somewhat like a court trial but on a tighter schedule and scope. Both the petitioner and the patent owner will have the opportunity to submit further briefing and evidence on the merits of the validity questions. Key aspects of the trial proceeding include:

• Patent Owner’s Response and Evidence: After institution, the patent owner is entitled to file a full response to the petition’s claims of unpatentability. This is different from the preliminary response. It is filed as part of the trial and can include affidavits, expert declarations, and other evidence to rebut the grounds of unpatentability asserted by petitioner. For example, the patent owner might present expert testimony explaining why the prior art doesn’t actually teach the claimed invention, or experiments showing the patent works as claimed.
• Petitioner’s Reply: The petitioner can then reply to the patent owner’s response, addressing such matters, arguments, and evidence raised by the owner. The PTAB’s rules often allow additional briefings like a patent owner sur-reply as well, to ensure each side can address new points.
• Discovery: Unlike in district court, discovery in a PGR is limited. The statute and rules restrict discovery to evidence directly related to factual assertions advanced by either party. In practice, “routine discovery” includes limited document exchange and cross-examination of affidavit/declaration witnesses. Each side can depose the other’s experts who submitted declarations. Additional discovery beyond the basics is only permitted by the Board upon a showing of necessity, i.e., “in the interests of justice” or good cause, per PTAB precedents. This limited discovery keeps the proceeding focused and efficient, avoiding the massive scale of document production typical in civil litigation. Each party must support its factual assertions with evidence, and they get a fair chance to test the other side’s evidence by deposing their expert(s) to probe the factual assertions advanced in their testimony.
• Motion Practice: The parties may file motions for certain requests during the trial. For example, parties can file motions to exclude evidence, or motions for joinder if another party wants to join the proceeding. A petitioner can also seek to submit supplemental information, e.g., newly discovered prior art, if done within the rules’ time frame (within one month of institution) and with PTAB approval. The PTAB can grant such a request upon a proper showing, but late additions are generally limited to keep the schedule on track.
• Oral Hearing: Both parties have the right to request an oral hearing before the PTAB. This hearing usually occurs near the end of the one-year trial period. At the hearing, attorneys for each side present arguments to the panel of administrative judges, and judges may ask questions. There is no jury. The panel of usually three administrative patent judges (APJs) ultimately acts as both fact-finder and decision-maker. The hearing is relatively short (one or two hours per side) and focused on key issues raised in the papers.
• Timeline: PGR is designed to be fast-tracked. By law, the PTAB should issue a final written decision within 1 year of instituting the review. This 1-year period can be extended by up to 6 months for good cause, e.g., in the case of exceptionally complex technology, but extensions are not routine. In cases with multiple petitions joined together, the schedule may be adjusted, but generally PGR aims to conclude no later than 18 months from institution even in the hardest cases. This statutory time frame provides far more certainty and speed than typical court litigation, which can take years.

Throughout the PGR trial, the burden of proof is on the petitioner to prove unpatentability of the challenged claims, and the standard is a preponderance of the evidence. This is notably a lower burden than in district court, where a patent is presumed valid and must be proven invalid by clear and convincing evidence. The PTAB judges will weigh the evidence and legal arguments from both sides under this lower standard when reaching a decision.

Patent Owner’s Option to Amend Claims

The post-grant review process not only allows cancellation of patent claims, but also provides the patentee a chance to amend the patent to overcome the challenge. Uniquely, in a PGR the patentee may file one motion to seek leave to amend the patent during the trial. Through this motion, the owner can cancel any challenged claims and/or propose a reasonable number of substitute claims to replace challenged claims. For example, if claim 1 is being challenged as obvious, the owner might propose a narrower substitute claim 1a that adds additional limitations, with the goal of overcoming the prior art.

However, amendments in PGR come with strict conditions and are relatively rare in practice. Any substitute claims cannot enlarge the scope of the original claims or introduce new matter (content that was not in the original application). In essence, you can only narrow or clarify claims, not broaden them. The patentee has a burden to show that the proposed new claims are supported by the original application and that they address the patentability raised in the petition. The petitioner gets to oppose the motion to amend, often by arguing the new claims are also unpatentable. The PTAB will then decide whether the amended claims should be allowed.

Only one motion to amend the claims is provided as a matter of right. Additional motions to amend are only permitted if the petitioner and patentee jointly request it (e.g., as part of a settlement) or if the patentee shows good cause. This ensures the proceeding is not delayed with endless claim changes. If the PTAB grants an amendment, either by allowing substitute claims or by the patentee canceling claims, and the new claims are found patentable in the PGR proceeding, the patent will be amended to include the new claims. The new or amended claims will have the same legal effect as a claim in a reissued patent, and can be enforced against any third party practicing the invention recited in the claims. However, third parties that were practicing the invention prior to the amendment to the patent may benefit from intervening rights protection. Intervening rights essentially shield third parties that were practicing the invention between the filing of the PGR proceeding and the amendment of the patent with the newly narrowed claims from liability.

Final Written Decision, Estoppel, and Appeal

At the end of the post-grant review trial, the PTAB issues a final written decision on the patentability of the challenged claims and any new claims added via amendment. This decision will explicitly determine, claim by claim, which claims are unpatentable and which are confirmed patentable. The PTAB’s decision is comprehensive: by statute, it must address every patent claim challenged by the petitioner and every new claim added in the proceeding. This requirement, reinforced by the Supreme Court’s SAS Institute decision, means you get a resolution on all issues raised, bringing clarity to the patent’s status.

Following a final decision, the USPTO will issue a certificate that formally documents the outcome: canceling any claims found unpatentable, confirming any claims that survived, and incorporating any amended claims that were allowed. If all claims are canceled, the patent is fully invalidated. If some claims survive, the patent remains in force with at least those claims.

Both parties have the right to appeal the final written decision. Under the law, an appeal from a PGR goes to the U.S. Court of Appeals for the Federal Circuit. For instance, a patent owner might appeal if their claims were canceled, arguing the PTAB erred in its analysis, or a petitioner might appeal if they feel a claim was wrongly upheld. The Federal Circuit will review the PTAB’s decision on legal issues, including claim interpretation or application of law, and the evidence on record, but giving deference to the PTAB’s fact-findings if it is supported by substantial evidence. This appellate review provides a check on the PTAB.

One of the most significant legal effects of a final PGR decision is estoppel. The AIA imposes estoppel to prevent a losing challenger from re-litigating the same issues in multiple forums. Specifically, after a final written decision, the petitioner and its real parties in interest and privies may not request or maintain any other proceeding in the USPTO on any claim that was raised or reasonably could have been raised in the PGR. This means the petitioner can’t turn around and file a new reexamination, an IPR, or another PGR on the same patent claims using invalidity bases or arguments that were available in the initial proceeding, but were not submitted. Likewise, the petitioner is estopped from asserting in civil litigation or in a proceeding before the International Trade Commission that the claim is invalid on any ground it raised or reasonably could have raised during the PGR. In short, PGR is a one-shot opportunity, you need to bring all your best prior art and arguments, because if you lose, you cannot try a different invalidity theory later in court, unless the grounds were genuinely unavailable to you during the PGR.

It’s worth noting that settlement is possible during PGR, and if a PGR is settled and dismissed before a final decision, estoppel typically does not attach to the petitioner. This allows parties to use PGR as leverage for a negotiated resolution without the harsh estoppel, as long as they settle in time. The PTAB will terminate the proceeding if both sides agree to settle and there is no public interest reason to proceed to a decision.

Advantages of Post-Grant Review for Challengers

For those seeking to challenge a patent, post-grant review offers several compelling advantages over traditional litigation or other USPTO proceedings:

• Broad Grounds and Strong Attack: As discussed, PGR allows the broadest possible grounds for challenging a patent, including prior art and non-prior-art issues. A challenger can throw everything into one proceeding, potentially invalidating a weak patent on multiple independent bases. This comprehensive approach can eliminate a patent before it gains value or becomes deeply entrenched. By contrast, an IPR or ex parte reexam is narrower in scope, and a district court lawsuit might be constrained by higher proof standards and procedural limits.
• Lower Burden of Proof: In PGR, invalidity only needs to be shown by a preponderance of the evidence. In a jury trial, a patent is presumed valid and must be proven invalid by clear and convincing evidence, a significantly higher bar. The more lenient standard in PGR makes it easier for challengers to prevail on close calls. Many patents that might withstand a court challenge with benefit of the doubt to the patent can be taken down in PGR where the scales are evenly balanced.
• Expert Decision-Makers: The case is decided by a panel of PTAB judges who are specialists in patent law, often with technical backgrounds. This specialized tribunal can be advantageous for a challenger when patents involve complex technology or nuanced legal issues. The judges are experienced in assessing prior art and patent claims, and there is no risk of a lay jury being confused by technical details. This often leads to more predictable, reasoned outcomes on patent validity.
• Speed and Efficiency: PGR is faster than litigation by design. The entire trial is usually completed about 12–18 months from institution. Thus, a challenger can get clarity on a patent’s validity quickly, rather than enduring a protracted 3-5 year court battle. PGR is also generally cheaper than district court litigation. While PGR costs can still be substantial, this is often a fraction of the cost of full patent litigation, which can run into the millions for protracted litigation. The cost savings come from the limited discovery and shorter timetable.
• Early Resolution and Business Certainty: PGR occurs early in a patent’s life (within the first 9 months), which means patent disputes can be resolved early as well. For a business, knocking out a competitor’s patent early can prevent that patent from ever being used to extract licensing fees or injunctions. It also discourages other would-be patentees from pursuing overly broad claims if they know challengers have a swift remedy. On the flip side, if the patent survives PGR, the patentee and the public gain certainty about the patent’s strength. This is valuable knowledge that allows businesses to make informed decisions: whether it’s safe to proceed with a product, whether to design around, or whether to license, etc.
• Possibility of Stay in Litigation: If litigation is already or soon to be underway, a PGR can facilitate a pause in the courtroom fight. As noted, if the challenger files a declaratory judgment action after the PGR, that action is automatically stayed. Even if an infringement lawsuit by the patentee is ongoing, courts often will consider staying the case pending a PTAB trial, since the PGR can simplify or moot the issues. This can save litigation costs and avoid conflicting outcomes. Essentially, PGR provides a single forum to potentially resolve the patent’s validity, rather than fighting on two fronts.
• Settlement and Estoppel Considerations: PGR rules encourage settlement. The parties can settle the case and end the proceeding at any time, and if they do so before final decision, the challenger faces no estoppel in court. This is a strategic advantage: a challenger can file the PGR, putting pressure on the patentee, and still retain the ability to walk away without losing legal options if a business resolution is reached early. In contrast, the old inter partes reexamination had no mechanism to stop upon settlement. The PTAB would continue regardless, which removed some leverage from challengers.

In summary, for a challenger, PGR offers a potent combination of comprehensiveness, speed, and a favorable forum that can increase the chances of invalidating a problematic patent efficiently. It effectively puts the patent on trial in front of experts, under rules that favor a thorough vetting of the patent’s merits.

PGR vs. Other Proceedings (IPR, CBM, and Reexamination)

It’s helpful to distinguish post-grant review from other post-grant validity challenges:

• Post-Grant Review (PGR) – Broad and early. As described, must be filed within 9 months of issuance, can challenge on any ground of invalidity (Sections 101, 102, 103, 112), threshold of “more likely than not” for institution, and results in broad estoppel on any ground that was or could have been raised. PGR is available only for AIA-era patents (effective filing date after March 15, 2013). It’s the most powerful review, but the catch is the short window after grant and the slightly higher bar to achieve institution .
• Inter Partes Review (IPR) – Focused and later. IPR is another AIA trial procedure, but it can only be filed after the PGR window closes (9 months after the patent issued). IPR is limited to patents and printed publications as evidence, and only on §102 (novelty) or §103 (obviousness) grounds. It cannot address any additional grounds under §101 or §112. The threshold for IPR institution is a “reasonable likelihood” that the petitioner will prevail on at least one claim, which is viewed as a bit easier to meet than PGR’s threshold. IPR also has a one-year deadline from being sued for infringement: i.e., if the patentee sues you, you must file IPR within a year. IPR estoppel applies to any ground raised or that reasonably could have been raised in the IPR, but since the scope of the IPR is narrower, the estoppel is effectively limited to invalidity based on prior art patents and publications. In practice, many challengers use IPR for older patents or when they missed the PGR window. It is an effective tool, but if your invalidity arguments require something like lack of written description or prior public use evidence, a PGR should be pursued.
• Covered Business Method (CBM) Review – Special and expired. CBM was a transitional post-grant review program under the AIA for certain “business method” patents, typically patents related to financial services. It had additional standing requirements: only those sued or charged with infringement of a financial business method patent could file and was available for pre-AIA patents. CBM used many of the same rules as PGR, including broad grounds for invalidity. However, CBM reviews were a temporary program that expired in 2020. No new CBM petitions can be filed now. CBM is largely of historical interest, but it is sometimes mentioned alongside PGR/IPR in discussions of post-grant proceedings. Essentially, PGR is now the primary route for broad challenges, since CBM is no longer available.
• Ex Parte Reexamination – Legacy option. Any person (even anonymously) can request an ex parte reexam of a patent at any time during the patent’s life by presenting a “substantial new question of patentability” based on patents or printed publications. If granted, the patent is reexamined by a patent examiner, not the PTAB. The requester has very limited participation rights: after initiating, it’s largely between the patentee and the examiner. Ex parte reexamination is useful for certain situations. It is cheaper and doesn’t carry estoppel in court for the requester, since technically only the USPTO is reconsidering the patent. But it’s limited to basically the same scope as IPR (validity is reviewed based only on patents and publication prior art) and can be much slower and less decisive. There is no guaranteed timeline for conclusion, and no adversarial hearing. Thus, while reexamination remains an option, it lacks the procedural robustness of PGR.
• Patent Appeals before the PTAB - Patent appeals are also heard before the PTAB, but are reviews of patentability issues raised in a patent application before it issues. They are petitions by a patent applicant to PTAB to challenge the legality and propriety of rejections of the patent application made in a patent office action by the patent examiner. Thus, they differ in nature from the other proceedings discussed herein, as they are not reviews of an issued patent.

In summary, PGR is unique in combining broad grounds with a fast, adjudicative process, but it must be utilized shortly after a patent is granted. IPR is the fallback for later challenges on narrower grounds. Reexamination is a slower, limited tool that still exists for prior art-based challenges. And CBM is no longer available for new filings. A petitioner must choose the procedure that fits the timing and grounds of their case.

Conclusion

For business owners facing potentially troublesome patents, post-grant review provides an effective and efficient procedure for challenging a patent of questionable validity. The PGR proceeding places patents under close scrutiny by experienced patent judges, applying the more favorable preponderance-of-evidence standard. If a patent truly lacks novelty, is obvious, or fails to meet formal legal requirements, PGR provides a swift mechanism to invalidate the patent and remove the threat it poses. On the other hand, if the patent survives PGR, it emerges confirmed validity, which will inform business strategy going forward.

The advantages in terms of grounds, speed, and success rate make a PGR an attractive option in the right circumstances. It has become an integral part of U.S. patent strategy since the AIA. By instituting a post-grant review with sufficient grounds, a petitioner can often either knock out an invalid patent or at least clarify the landscape, thereby avoiding costly litigation down the road. In sum, post-grant review is a powerful tool in the U.S. patent system that helps to eliminate unworthy patents.

If you are looking for guidance on post-grant review proceedings or other patent matters, contact our office for a free consultation.

© 2025 Sierra IP Law, PC. The information provided herein does not constitute legal advice, but merely conveys general information that may be beneficial to the public, and should not be viewed as a substitute for legal consultation in a particular case.