Clantech v. CoStar & Duolingo: Federal Circuit Affirms OFDM Patent Unpatentable
Clantech, Inc. appealed to the Federal Circuit after its two patents covering dynamic configuration of flexible OFDM PHY transport data frames were found unpatentable. A per curiam panel of three judges — Lourie, Reyna, and Cunningham — unanimously affirmed the ruling in 694 days, extinguishing Clantech’s IP position against both CoStar and Duolingo.
Federal Circuit kills Clantech’s OFDM patents in unanimous per curiam ruling
Clantech, Inc. filed Case No. 24-1360 at the Court of Appeals for the Federal Circuit on 17 January 2024, appealing a prior determination that US9866421B2 and US9886421 — both directed to dynamic configuration of a flexible orthogonal frequency division multiplexing (OFDM) PHY transport data frame — were unpatentable. The defendants, CoStar Realty Information, Inc. and Duolingo, Inc., were represented by Latham & Watkins LLP, a team led by Ashley M. Fry, Gabriel K. Bell, and Inge A. Osman.
The Federal Circuit closed the case on 11 December 2025 with a terse per curiam order from Judges Lourie, Reyna, and Cunningham: ‘AFFIRMED.’ Under Federal Circuit appellate procedure, affirmance means the panel found no reversible legal error in the lower tribunal’s unpatentability finding. Both patents — US9866421B2 and US9886421 — accordingly remain cancelled or invalid, and Clantech loses all enforcement rights against CoStar, Duolingo, and the broader market.
At 694 days, the appeal ran longer than many CAFC patent appeals, suggesting substantive briefing rather than early dismissal. The unpatentability basis — consistent with an invalidity or cancellation action — indicates the patents likely failed on prior art or patent-eligibility grounds, though the per curiam form of the affirmance means the court did not publish a detailed opinion. The absence of a written opinion leaves the precise legal rationale unavailable from the public record.
Filing to Unpatentable in 694 days
694 days from filing to Federal Circuit decision — above the median for CAFC patent appeals
Federal Circuit affirms: what the ruling means for both parties
Affirmance: the lower unpatentability ruling now stands permanently
At the Federal Circuit, ‘AFFIRMED’ means the appellate panel found no reversible error — whether legal or factual — in the decision below. The lower tribunal’s determination that US9866421B2 and US9886421 are unpatentable is now the final word at this appellate level. Clantech bore the burden of demonstrating error; the per curiam panel unanimously concluded it did not meet that burden.
No reversible error foundClantech loses both patents — enforcement rights fully extinguished
With affirmance, Clantech’s two OFDM PHY transport frame patents are confirmed unpatentable. Clantech cannot enforce either patent against CoStar, Duolingo, or any third party. Further appeal would require a petition for certiorari to the U.S. Supreme Court — a rarely granted avenue — or a legislative fix. Commercially, Clantech’s IP position in the OFDM transport framing space is effectively eliminated.
Patents cancelled — no enforcement pathCoStar and Duolingo secure full clearance from Clantech’s OFDM claims
Both CoStar Realty Information and Duolingo emerge with their operations fully insulated from any future assertion of these two patents. The affirmance raises the res judicata bar: Clantech cannot relitigate the patentability of these claims. Latham & Watkins’s defence strategy — pursued to final Federal Circuit judgment rather than settlement — produced a clean, permanent outcome for both defendants.
Defendants fully clearedOFDM PHY transport patents face heightened scrutiny after Clantech loss
The unanimous affirmance signals that OFDM PHY transport data frame patents of this type face serious validity headwinds at the Federal Circuit. Companies in wireless communications, networking, and adjacent software sectors holding or targeting similar OFDM transport configuration patents should reassess portfolio strength. The precedent — even without a written opinion — suggests this claim architecture is vulnerable to cancellation or invalidity challenges.
OFDM patent risk elevatedFull party and counsel information
| Role | Name | Type | Detail |
|---|---|---|---|
| Plaintiff | Clantech, Inc. | Company | OFDM telecommunications IP holder — asserting US9866421B2 and US9886421Search in Eureka ↗ |
| Defendant | CoStar Realty Information, Inc. | Company | CoStar Realty Information, Inc. (real estate data) and Duolingo, Inc. (language learning platform)Search in Eureka ↗ |
| Co-Defendant | Duolingo, Inc. | Company | Search in Eureka ↗ |
| Plaintiff counsel | James C. Watson | Attorney | Counsel for Clantech, Inc.Search in Eureka ↗ |
| Plaintiff law firm | TraskBritt PC | Law Firm | Representing Clantech, Inc.Search in Eureka ↗ |
| Defendant counsel | Ashley M. Fry | Attorney | Counsel for CoStar Realty Information, Inc.Search in Eureka ↗ |
| Defendant counsel | Gabriel K. Bell | Attorney | Counsel for CoStar Realty Information, Inc.Search in Eureka ↗ |
| Defendant counsel | Inge A. Osman | Attorney | Counsel for CoStar Realty Information, Inc.Search in Eureka ↗ |
| Defendant law firm | Latham & Watkins, LLP | Law Firm | Representing CoStar Realty Information, Inc.Search in Eureka ↗ |
| Presiding judge | Judge N/A | Judge | Court of Appeals for the Federal CircuitSearch in Eureka ↗ |
Official order — verbatim text
The verdict reads: ‘AFFIRMED’ — issued per curiam by Judges Lourie, Reyna, and Cunningham. At the Federal Circuit, per curiam affirmance under the appellate standard of review means the panel found no reversible error of law and no clear error of fact in the unpatentability determination below. The brevity of the disposition — no authored opinion — suggests the panel viewed the appeal as legally straightforward. For Clantech, all enforcement rights under both patents are permanently extinguished. For CoStar and Duolingo, the affirmance constitutes a final, binding clearance.
US9866421B2 & US9886421 — Dynamic OFDM PHY Transport Data Frame Configuration
US9866421B2 (application US14/821107) and US9886421 (application US15/581921) both cover dynamic configuration of a flexible orthogonal frequency division multiplexing (OFDM) PHY transport data frame. OFDM is a foundational modulation technique used across 4G LTE, 5G NR, Wi-Fi, and broadband communications. Patents in this space typically protect methods for dynamically allocating subcarrier resources, guard intervals, or frame structures to optimise spectral efficiency — a commercially critical capability in modern wireless infrastructure.
The sequential application numbers indicate a likely continuation relationship, suggesting Clantech sought to extend protection across related claim sets from a common priority disclosure. Despite the commercial significance of OFDM transport framing in wireless networking and any application layer relying on it, both patents have now been confirmed unpatentable by the Federal Circuit. Any entity — from telecom infrastructure providers to SaaS platforms using OFDM-based connectivity — that previously faced risk from these patents now operates free of Clantech’s claims.
Should you run an FTO against US9866421B2 and US9886421?
Although both Clantech patents have been confirmed unpatentable, R&D and product teams working on OFDM PHY layer implementations — including dynamic subcarrier allocation, transport frame configuration, and flexible waveform design — should still conduct freedom-to-operate analysis. Clantech may hold continuation applications with surviving claims. Separately, other patent holders in the OFDM transport framing space may assert overlapping rights. This case does not provide blanket clearance across the OFDM landscape.
PatSnap Eureka’s FTO Search Agent can map the full continuation family of US9866421B2 and US9886421, identify sibling applications with potentially live claims, and surface other OFDM PHY transport patents that could pose assertion risk. For product teams building on OFDM-based physical layers — whether in wireless hardware, network infrastructure, or communication-dependent SaaS — Eureka provides claim-level landscape analysis to support clearance decisions before product launch.
Run a freedom-to-operate analysis on US9866421B2 to assess your product’s exposure
Run FTO in Eureka →Similar OFDM and wireless PHY patent appeals at the Federal Circuit
Cases involving OFDM, physical-layer wireless patents, and unpatentability affirmances at the Federal Circuit — curated for IP practitioners in the wireless and communications sector.
What Clantech v. CoStar signals for the OFDM and wireless IP landscape
A unanimous per curiam affirmance of unpatentability sends a clear signal about OFDM transport frame claim viability at the Federal Circuit.
Per curiam affirmance without opinion limits precedential guidance but signals consensus
The Federal Circuit’s per curiam form — three judges, no authored opinion — confirms unanimity and suggests the panel found the unpatentability determination straightforward. For practitioners, this limits citable precedent but reinforces that OFDM PHY transport configuration claims of this architecture face a difficult appellate path. Challengers can point to this outcome in future validity disputes.
Duolingo’s presence as a defendant highlights non-obvious OFDM licensing targets
Clantech’s assertion against both a real-estate data platform (CoStar) and a language-learning app (Duolingo) suggests a broad, technology-agnostic licensing strategy targeting any entity using flexible OFDM data framing in their infrastructure. Companies in software-as-a-service sectors that rely on OFDM-based communication layers should monitor similar patent assertion campaigns targeting infrastructure-layer wireless protocols.
Clantech v CoStar — key questions answered
The Federal Circuit affirmed the unpatentability of both patents asserted by Clantech — US9866421B2 and US9886421 — in a per curiam order by Judges Lourie, Reyna, and Cunningham. The case closed on 11 December 2025 after 694 days. Clantech’s enforcement rights against CoStar and Duolingo are permanently extinguished.
Clantech asserted US9866421B2 (application US14/821107) and US9886421 (application US15/581921). Both patents cover dynamic configuration of a flexible orthogonal frequency division multiplexing (OFDM) PHY transport data frame — a core technology in 4G, 5G, Wi-Fi, and modern broadband communications infrastructure.
The Federal Circuit issued a per curiam affirmance without a written opinion, meaning the specific legal rationale is not publicly available from the appellate record. The basis of termination is listed as ‘Unpatentable’ following an invalidity/cancellation action, consistent with a prior PTAB or equivalent proceeding. The per curiam form suggests the panel viewed the unpatentability determination as legally uncontroversial.
The public record does not specify the precise infringement theory against Duolingo. Clantech’s assertion against both CoStar (real estate data) and Duolingo (language learning) is consistent with a technology-agnostic licensing strategy targeting entities whose software infrastructure relies on OFDM-based communications layers, rather than companies that manufacture wireless hardware directly.
Following a Federal Circuit affirmance, the only further appellate avenue is a petition for a writ of certiorari to the U.S. Supreme Court — an extraordinary remedy granted in fewer than 2% of petitions. Absent Supreme Court intervention, the unpatentability findings for US9866421B2 and US9886421 are final and binding, and Clantech cannot relitigate these claims.
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