Patent Validity · PTAB · District Court
Challenging a Patent
Four distinct paths for attacking US patent validity — each with different deadlines, grounds, estoppel consequences, costs, and decision makers. Choosing the wrong forum at the wrong time can foreclose better options.
35 U.S.C. §§ 302–307
Ex Parte Reexamination
Anyone — including an anonymous third party — can request ex parte reexamination. The USPTO must grant the request if the requester presents 'a substantial new question of patentability' (SNQ) based on prior art patents or printed publications. After granting, a single examiner conducts the reexamination as a dialogue between the examiner and the patent owner. The requester is not a party after filing — they cannot participate in responses or hearings.
Grounds
§§ 102 and 103 only; prior art must be patents or printed publications. Cannot challenge on § 101 (eligibility) or § 112 (enablement, written description). No public use, prior sales, or non-documentary evidence.
Who can file
Any person, including anonymous third parties (anonymity requests accepted); the patent owner itself (to correct prior art issues).
Filing deadline
No time limit — can be filed any time during the patent's term and even after it expires (if the patent is being asserted in litigation).
Institution standard
Substantial new question of patentability (SNQ) — a relatively low bar; the USPTO must only conclude the prior art raises a new question that was not adequately considered during original prosecution.
Estoppel
None. The requester is not estopped from raising the same prior art in subsequent district court litigation or IPR. This is the major strategic advantage of ex parte reexam over IPR.
Claim amendments
Patent owner may amend claims — both narrowing amendments and (rarely) broadening amendments (which are limited). This is an advantage over district court invalidity.
USPTO fees (large entity)
~$12,000 (USPTO filing fee: $12,000 large entity, $6,000 small entity, $3,000 micro entity); no attorney fees counted.
Timeline
12–24 months for a decision; USPTO statistics show about 66% of completed reexaminations result in amended or canceled claims.
Appeal path
Patent owner can appeal examiner's rejection to PTAB and Federal Circuit. Requester has no appeal rights.
When to use
Best used when: (1) you have strong prior art but don't want IPR estoppel; (2) you want to remain anonymous; (3) litigation is distant and you want slow-burn invalidity pressure; (4) you want to create prior art prosecution history that limits claim scope even if claims survive.
35 U.S.C. §§ 311–319
Inter Partes Review
Inter Partes Review (IPR) is the most frequently used post-grant validity challenge at the USPTO. Introduced by the America Invents Act (AIA, 2011), IPR replaced the prior 'inter partes reexamination' process with a faster, more adjudicatory PTAB proceeding before a three-judge panel of Administrative Patent Judges (APJs). IPR allows any third party — most often accused infringers, competitors, or patent challengers — to petition PTAB to cancel claims based on prior art patents or printed publications.
Grounds
§§ 102 and 103 only; prior art must be patents or printed publications. Cannot use § 101, § 112, public use, or on-sale bar. This is a critical limitation: if the primary invalidity theory is § 101 ineligibility (e.g., software-patent challenge under Alice), IPR is NOT the right vehicle — use PGR (within 9 months of grant) or district court.
Who can file
Any person who is not the patent owner. Person who has filed a civil action challenging the validity of a claim is barred. Must identify all real parties in interest (RPI) and privies — failure to correctly identify RPI is fatal to the petition.
Filing deadline
MUST BE FILED WITHIN 1 YEAR of the date the petitioner (or the real party in interest or privy) is SERVED with a complaint alleging infringement of the patent (35 U.S.C. § 315(b)). This is a HARD BAR — not subject to equitable tolling (Thryv v. Click-to-Call, S.Ct. 2020 — § 315(b) time bar is unreviewable on appeal). If a complaint is served more than 1 year before petition, IPR is barred. Strategy: file IPR BEFORE being served if possible, or carefully track service date.
Institution standard
Institution threshold: 'reasonable likelihood that the petitioner would prevail with respect to at least 1 of the claims challenged' (§ 314(a)). After SAS Institute v. Iancu (S.Ct. 2018): PTAB must either institute on ALL challenged claims or deny — cannot institute on a subset of claims. Discretionary denial: PTAB may deny institution even if the threshold is met — most commonly under Apple Inc. v. Fintiv (PTAB precedential 2020): 6-factor test considers how advanced parallel district court litigation is (if trial is imminent, PTAB may deny IPR as redundant).
Estoppel
STRONG estoppel if IPR proceeds to Final Written Decision: petitioner (and all RPI/privies) are estopped from asserting in district court, ITC, or before USPTO that the challenged patent claim is invalid on any ground that the petitioner RAISED OR REASONABLY COULD HAVE RAISED during IPR (35 U.S.C. § 315(e)). 'Reasonably could have raised' includes prior art that was publicly available and discoverable. Estoppel does NOT apply if the petition is denied (no institution) — another reason for the 'file and deny' strategy. No estoppel for § 101 or § 112 grounds (which cannot be raised in IPR anyway).
Claim amendments
Patent owner may file ONE motion to amend claims (37 C.F.R. § 42.121). Under Aqua Products v. Matal (Fed. Cir. 2017, en banc): petitioner bears the burden of proving proposed amended claims are unpatentable (not patent owner's burden to prove patentability). Conditional amendments common: 'if independent Claim 1 is canceled, substitute Claim 21 as follows...'
USPTO fees (large entity)
USPTO fees (large entity, 2024 approximate): Petition fee for up to 20 claims = $19,500; for each additional claim over 20 = $475. Post-institution request fee for up to 15 claims = $22,500; each additional claim above 15 = $550. Total USPTO fees alone for a typical 20-claim petition through institution: approximately $41,000–$48,000. Attorney fees: typically $60,000–$150,000 for petition through final written decision.
Timeline
From institution to Final Written Decision: 12 months (§ 316(a)(11)); PTAB may extend by 1 month for good cause. From petition filing to institution decision: typically 3–6 months. Full timeline from filing petition to Final Written Decision: typically 16–20 months.
Appeal path
Either party can appeal Final Written Decision to the Federal Circuit. Federal Circuit review: legal issues de novo; factual determinations reviewed for substantial evidence.
When to use
Best used when: (1) you have strong prior-art publications or patents; (2) you can accept the estoppel consequence (you're confident you'll win or that the claims can be narrowed); (3) the patent is new (within 1 year of complaint service); (4) you want a faster, less expensive alternative to full district court invalidity litigation; (5) you want to avoid jury trial on invalidity (PTAB panel is more technically sophisticated than average jury).
35 U.S.C. §§ 321–329
Post-Grant Review
Post-Grant Review (PGR) is the most powerful USPTO validity challenge, allowing attack on any ground — including § 101 patent-eligibility and § 112 enablement/written description. The critical constraint: PGR must be filed within 9 months of the patent's grant or reissuance. After 9 months, only IPR (or ex parte reexam or district court) is available. PGR applies only to AIA patents — patents in which all claims have an effective filing date on or after March 16, 2013 (the date the AIA first-inventor-to-file system took effect).
Grounds
ANY ground under § 282(b)(2) or (3): § 101 (patent-eligible subject matter), § 102 (novelty), § 103 (obviousness), § 112 (written description, enablement, definiteness), prior public use, prior commercial sale, on-sale bar. This is the ONLY USPTO post-grant proceeding that can challenge § 101 and § 112.
Who can file
Any person who is not the patent owner, and who has not previously filed a civil action challenging validity. Must identify all real parties in interest. Cannot file PGR if you previously filed IPR on the same patent.
Filing deadline
MUST be filed within 9 months of the date of grant or reissuance of the challenged patent. This is a hard, absolute deadline — no exceptions. After 9 months, PGR jurisdiction closes entirely.
Institution standard
Institution threshold: 'more likely than not that at least 1 of the claims challenged in the petition is unpatentable' — a higher bar than IPR's 'reasonable likelihood' standard. Alternatively, PTAB may institute PGR if 'the petition raises a novel or unsettled legal question that is important to other patents or patent applications' (§ 324(b)).
Estoppel
Same as IPR: if PGR proceeds to Final Written Decision, petitioner and RPI/privies are estopped from raising (in district court, ITC, USPTO) any ground that was raised or reasonably could have been raised during PGR (§ 325(e)). Because PGR grounds are broader (ANY ground), estoppel is correspondingly broader — a significant strategic consideration. No estoppel if petition denied.
Claim amendments
Same procedure as IPR: patent owner may file one motion to amend; petitioner has burden of showing proposed amended claims are unpatentable.
USPTO fees (large entity)
USPTO fees (large entity, 2024 approximate): Petition fee for up to 20 claims = $40,000; each additional claim over 20 = $900. Post-institution request for up to 15 claims = $55,000; each additional claim = $1,100. Significantly more expensive than IPR.
Timeline
Institution to Final Written Decision: 12 months (extendable 1 month). Similar total timeline to IPR: 16–20 months from petition to final decision.
Appeal path
Either party can appeal Final Written Decision to the Federal Circuit; same standard as IPR appeals.
When to use
Best used when: (1) the patent was recently granted (within 9 months); (2) the primary invalidity theory is § 101 (Alice/Mayo ineligibility) or § 112 (overbroad functional claim, undisclosed embodiments, genus claims); (3) you are willing to accept broad estoppel because you are highly confident in the invalidity theory; (4) the patent is an AIA patent (effective filing date on/after March 16, 2013).
35 U.S.C. § 282
District Court Invalidity Defense
In district court patent litigation, invalidity is an affirmative defense and counterclaim that a defendant can raise in response to any infringement complaint. There are no special forms, no petition fees, and no PTAB pre-screening. The defendant simply asserts invalidity in its answer and pursues it through the full litigation process — discovery, claim construction (Markman hearing), expert reports, summary judgment, and, if needed, trial.
Grounds
Any ground under 35 U.S.C. § 282(b): §§ 101, 102, 103, 112; prior public use or sale; failure to disclose best mode (pre-AIA); derivation; prior art not limited to patents and printed publications — sworn testimony of prior use, public knowledge, commercial sales, and research presentations all count. Prior commercial sale (on-sale bar) and public use are particularly valuable in district court (where they cannot be used in IPR or ex parte reexam).
Who can file
Only available as a defense (or counterclaim) by a defendant (or declaratory judgment plaintiff) in active district court litigation. Cannot be filed proactively outside litigation (use IPR/PGR/reexam for proactive challenges).
Filing deadline
No deadline for raising invalidity — it can be raised as a defense at any point in active litigation before final judgment (subject to waiver if pled too late). A defendant doesn't have to file within 1 year of receiving a complaint; only IPR has that constraint.
Institution standard
Clear and convincing evidence (Microsoft Corp. v. i4i Limited Partnership, S.Ct. 2011) — a high burden that reflects the deference owed to the USPTO's examination. This is the highest invalidity standard of any forum: higher than PTAB's 'reasonable likelihood' (IPR institution) and 'preponderance of evidence' (PTAB merits).
Estoppel
No estoppel from raising grounds that were not litigated. If an invalidity issue is actually litigated and decided, issue preclusion (collateral estoppel) bars re-litigation of that specific issue with the same parties. 35 U.S.C. § 315(e) IPR estoppel does NOT apply to district court invalidity defenses raised independently of an IPR.
Claim amendments
Claims cannot be amended in district court — the patent is litigated with its issued claims. If claims are found invalid, they are declared invalid; the patent owner cannot substitute narrower claims. (Compare to USPTO proceedings where amendment is available.)
USPTO fees (large entity)
No USPTO filing fee, but full litigation costs. Patent litigation through trial costs $3M–$10M+ per side. Summary judgment motions on invalidity: $500K–$2M in attorney fees. Expert witness fees alone: $200K–$1M+.
Timeline
Markman hearing (claim construction): typically 12–18 months after complaint. Trial: typically 2–4 years after complaint. Faster in rocket dockets (Western District of Texas, Delaware) vs. slower courts. ITC Section 337 investigation: faster — 12–18 months to full hearing, but ITC does not cancel patent claims.
Appeal path
District court judgment → Federal Circuit (de novo on claim construction; clear error on underlying factual findings per Teva v. Sandoz, S.Ct. 2015). Federal Circuit invalidity decisions are binding nationally.
When to use
Best used when: (1) you need § 101 or public use/on-sale invalidity grounds (not available in IPR); (2) IPR is time-barred (more than 1 year since complaint was served); (3) you have non-documentary prior art (prior use, experimental work, sales) that can't be used in IPR/reexam; (4) you want a jury to decide invalidity (juries are more unpredictable — sometimes better for defendant); (5) you are already in litigation and adding invalidity costs little incrementally.
Side by Side
Comparison: all four proceedings
| Feature | Ex Parte Reexam | IPR | PGR | District Court |
|---|---|---|---|---|
| Available grounds | §102/103 — patents + printed pubs only | §102/103 — patents + printed pubs only | ANY — §101, §102, §103, §112, public use, on-sale | ANY — including public use, on-sale, prior public knowledge |
| Who can file | Anyone (anonymous OK) | Third parties only; must disclose all real parties in interest | Third parties only; must disclose all real parties in interest | Defendant/declaratory judgment plaintiff in litigation |
| Filing deadline | None — any time during patent term | Within 1 year of service of infringement complaint (HARD BAR) | Within 9 months of grant or reissuance (HARD BAR) | Any time in active litigation (subject to waiver) |
| Institution standard | Substantial new question of patentability (SNQ) | Reasonable likelihood of prevailing on ≥1 claim | More likely than not ≥1 claim is unpatentable | N/A — no pre-screening; all defenses proceed to trial |
| Invalidity standard | Preponderance of evidence (examiner decision) | Preponderance of evidence (PTAB panel) | Preponderance of evidence (PTAB panel) | Clear and convincing evidence (jury or judge) — highest bar |
| Decision maker | Single USPTO examiner | 3-judge PTAB panel (APJs) | 3-judge PTAB panel (APJs) | Federal district court judge + jury (if demanded) |
| Estoppel consequence | None — no estoppel for requester | STRONG — if FWD issued, estopped on all grounds raised or reasonably raisable in district court, ITC, USPTO | STRONG — same as IPR, but broader because PGR grounds are broader | Issue preclusion only on actually litigated issues; no special patent estoppel |
| Claim amendments | Patent owner can amend during proceeding | One motion to amend; petitioner bears burden on amended claims | One motion to amend; same as IPR | No amendments — issued claims only |
| USPTO fees (large entity, ~2024) | $12,000 | $41,500–$48,000 typical (petition + institution) | $95,000–$105,000 typical (petition + institution) | No USPTO fee (litigation costs $3M–$10M+) |
| Timeline | 12–24 months | 12–16 months from institution; 16–20 months from petition | 12–16 months from institution; 16–20 months from petition | 2–4 years (faster in rocket docket courts) |
| Anonymous filing | Yes — anonymity request forms available | No — must identify all real parties in interest | No — must identify all real parties in interest | No — defendant identity known |
| Non-documentary prior art | No — patents and printed publications only | No — patents and printed publications only | Yes — public use, sales, demonstrations allowed | Yes — public use, sales, experimental evidence, sworn testimony |
| §101 / §112 grounds | No | No | Yes | Yes |
| Available for pre-AIA patents | Yes | Yes | No (AIA patents only; CBM sunset September 2020) | Yes |
Key Cases
Landmark decisions shaping patent challenges
Oil States Energy Services v. Greene's Energy Group
S.Ct. 2018IPR does not violate Article III (requiring independent judiciary) or the Seventh Amendment (jury trial right). Patents are a 'public franchise' — the government may reconsider its grant without providing an Article III court or jury. IPR is constitutionally valid.
SAS Institute v. Iancu
S.Ct. 2018PTAB must institute IPR on ALL claims challenged in the petition or deny the petition entirely. It cannot selectively institute on a subset of claims. If PTAB institutes, it must address every claim and ground in the final written decision.
Thryv, Inc. v. Click-to-Call Technologies, LP
S.Ct. 2020The § 315(b) one-year time bar (1 year from service of infringement complaint) is unreviewable on appeal. PTAB's decision to institute over a § 315(b) objection cannot be challenged at the Federal Circuit. This makes the 1-year deadline absolute and unappealable.
Microsoft Corp. v. i4i Limited Partnership
S.Ct. 2011Patent invalidity in district court must be proven by clear and convincing evidence — the highest civil standard. The presumption of patent validity (35 U.S.C. § 282) reflects congressional intent to require strong proof of invalidity in Article III courts.
Apple Inc. v. Fintiv (PTAB Precedential)
PTAB 2020PTAB may discretionarily deny an IPR petition — even if the merits threshold is met — if parallel district court litigation is sufficiently advanced. Six factors: (1) stay likelihood; (2) proximity of trial date; (3) investment in parallel case; (4) overlap of issues; (5) party identity; (6) other Intel Corp. v. VLSI factors. Most contested PTAB discretionary denial standard; frequently challenged at the Federal Circuit.
Aqua Products v. Matal
Fed. Cir. 2017 (en banc)In IPR proceedings, the petitioner bears the burden of proving that proposed amended claims are unpatentable. The patent owner does not bear the burden of proving that proposed amended claims are patentable. This makes IPR claim amendments a viable strategy for patent owners.
FAQ
Frequently asked questions
What is the fastest way to challenge an issued US patent?
Inter Partes Review (IPR) delivers the fastest binding decision — typically 16–20 months from petition to final written decision, with PTAB institution decisions in 3–6 months. However, IPR is restricted to prior-art challenges under §§ 102 and 103 (prior art patents and printed publications only) and must be filed within 1 year of the date you are served with an infringement complaint. If you need to challenge § 101 patent-eligibility or § 112 enablement, and the patent was granted within the last 9 months, Post-Grant Review (PGR) provides the fastest path for those grounds. For the broadest attack — using prior public use, on-sale bar, § 101, and § 112 grounds without a filing deadline — district court invalidity defense is available in active litigation, but takes 2–4 years to reach a final judgment. The fastest overall with the most grounds: PGR within 9 months of grant, if the patent is an AIA patent and § 101 or § 112 is in play.
What is IPR estoppel and how does it affect patent litigation strategy?
IPR estoppel is one of the most consequential strategic considerations in patent litigation. Under 35 U.S.C. § 315(e), if an IPR petition proceeds to a Final Written Decision, the petitioner (and all real parties in interest and their privies) are estopped from asserting in district court, ITC, or any USPTO proceeding that any claim of the patent is invalid on any ground that the petitioner raised or reasonably could have raised during IPR. 'Reasonably could have raised' is interpreted broadly — it includes all prior art that was publicly available and discoverable, whether or not the petitioner actually included it in the IPR petition. This means: (1) if you win on Grounds A and B in IPR but lose on Grounds C and D, you are estopped from raising C and D in district court if they were known prior art that you reasonably could have raised; (2) this can destroy significant parts of a defendant's invalidity case that would otherwise be available in district court. Estoppel does NOT apply if the IPR petition is denied (no institution). This creates a perverse incentive: some defendants prefer to have their IPR denied so they can preserve their full invalidity case for district court. Estoppel does not apply to § 101 or § 112 grounds (which cannot be raised in IPR anyway) or to on-sale bar and prior public use evidence (also cannot be raised in IPR). Strategy: carefully scope your IPR petition to include ONLY the strongest grounds if you want to preserve other invalidity arguments for district court — but note that 'reasonably could have raised' may still reach prior art you omit.
Can I challenge a patent on § 101 grounds (abstract idea, patent-eligibility) at the USPTO?
Yes, but only in Post-Grant Review (PGR) — and only within 9 months of the patent's grant date. Inter Partes Review (IPR) and ex parte reexamination are limited to §§ 102 and 103 (prior-art novelty and obviousness) — they cannot be used to raise § 101 patent-eligibility challenges. If you want to challenge a patent under Alice/Mayo (software or business method patents), or Myriad (natural phenomena, laws of nature), your options are: (1) PGR: available within 9 months of grant for any AIA patent — allows § 101 plus any other invalidity ground; most complete USPTO validity challenge; (2) District court invalidity defense: available in active litigation at any time; § 101 is a question of law for the judge (no jury), decided on claim construction + the Alice/Mayo framework; often pursued via early summary judgment or 12(c) motion on the pleadings; clear and convincing evidence standard applies. Note: § 101 challenges in district court are typically decided much earlier in the case (often on pleadings or early summary judgment) than § 102/103 challenges because § 101 is a legal question requiring no expert testimony — this makes it an attractive early litigation move when the patent is a software or business-method patent.
What is the difference between a patent being 'canceled' in IPR and being 'held invalid' in district court?
The legal effect differs in an important way. When PTAB cancels patent claims in a Final Written Decision following IPR or PGR: the claims are canceled from the patent register — the cancellation has in rem effect and applies against everyone, not just the petitioner. If a patent claim is canceled, it is null and void as if it never existed — no one can be infringed upon it, no one needs a license, and the patent owner cannot sue on it. This is stronger, in one sense, than district court invalidity. When a district court holds a patent claim invalid: the judgment is technically binding only on the parties (the plaintiff patent owner and the defendant who litigated the case). In principle, the patent owner could sue a different defendant on the same claim. However: (1) because invalidity is not personal to any defendant, courts regularly follow prior invalidity rulings as persuasive authority; (2) the doctrine of offensive non-mutual collateral estoppel does not apply in patent cases (Blonder-Tongue Laboratories v. University of Illinois Foundation, S.Ct. 1971 — actually established that a patent adjudicated invalid against one defendant cannot be relitigated by the same patent owner against a different defendant who reasonably presents the same evidence of invalidity). So in practice, a district court invalidity ruling has a near-in rem effect as well. The practical difference: IPR/PGR cancellation removes the patent from the register immediately; district court invalidity requires a judgment and is technically party-specific even if practically universal.
How does the Fintiv doctrine affect IPR strategy for defendants already in district court litigation?
The Apple Inc. v. Fintiv precedential PTAB decision (2020) created a six-factor test PTAB uses to decide whether to discretionarily deny an IPR petition when there is a parallel district court case already underway. The six Fintiv factors: (1) Whether the district court has granted or denied a stay of litigation pending IPR; (2) Proximity of the trial date — the closer the district court trial date, the less likely PTAB will institute; (3) Investment by the parties and court in the parallel proceeding — more investment = more likely denial; (4) Overlap between IPR grounds and district court invalidity defenses — greater overlap favors denial; (5) Whether petitioner and defendant are the same — if same party, favors denial; (6) Other circumstances, including merits of the petition. Fintiv created significant controversy and uncertainty. High-impact courts with fast dockets (Western District of Texas, Delaware) often set trial dates 12–18 months out, making IPR institution unlikely under Fintiv. The USPTO Director issued guidance and a Final Rule (December 2022) limiting the most aggressive Fintiv applications. Strategies to survive Fintiv: (1) file IPR before or very soon after the infringement complaint is served (before the parallel case becomes 'advanced'); (2) file a motion to stay litigation pending IPR — a granted stay counsels in favor of institution; (3) limit IPR grounds to those not raised in district court (reduces 'overlap'); (4) choose petitions on the strongest prior art with compelling merits (Factor 6 can override other factors for a very strong petition); (5) consider ITC complainant context where ITC proceedings move to trial in 12–18 months, making Fintiv even more challenging.
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