The US Court of Appeals for the Federal Circuit affirmed the Patent Trial & Appeal Board, concluding that the retroactive effect of a correction of inventorship under 35 U.S.C. § 256 does not bar the application of forfeiture principles in inter partes review (IPR) proceedings, and that a patent owner that fails to timely raise an antedating theory during an IPR may forfeit reliance on a later corrected inventorship to resurrect that theory. Implicit, LLC v. Sonos, Inc., Case Nos. 20-1173; -1174 (Fed. Cir. Mar. 9, 2026) (Taranto, Stoll, Cunningham, JJ.)
Implicit owns patents directed to content rendering that originally named Edward Balassanian and Scott Bradley as co-inventors. Sonos filed IPR petitions against both patents, asserting unpatentability under 35 U.S.C. §§ 102 and 103, primarily based on Janevski, which had an effective prior art date of December 11, 2001.
To avoid Janevski as prior art, Implicit argued that the inventions were conceived and reduced to practice before December 11, 2001. It contended that Balassanian and Bradley conceived of the inventions and collaborated with another engineer, Guy Carpenter, to implement the invention prior to December 2001. Implicit argued that Carpenter’s work inured to the benefit of the named inventors, thereby antedating Janevski. The Board rejected Implicit’s argument and found the challenged claims unpatentable as anticipated or obvious over Janevski. The Board found Implicit’s evidence insufficient to establish conception and communication of the invention by Carpenter in a manner that would support an earlier reduction to practice.
Following the Federal Circuit’s and Supreme Court’s decisions in Arthrex v. Smith & Nephew addressing the Appointments Clause as applied to IPR proceedings, the case was remanded to permit Director review. While proceedings were ongoing, Implicit sought correction of inventorship under 35 U.S.C. § 256 to add Carpenter as a co-inventor. The United States Patent & Trademark Office (USPTO) granted the request and issued certificates of correction in August 2022. The Federal Circuit remanded the case to the Board to determine what impact, if any, the corrections had on the prior final written decisions. The Board concluded that equitable doctrines, including forfeiture, precluded Implicit from relying on the corrected inventorship to advance a new antedating theory. Implicit appealed.
The appeal presented two principal questions:
- Whether the retroactive effect of a correction of inventorship under § 256 forecloses application of forfeiture principles in an IPR proceeding.
- Whether the Board abused its discretion in finding that Implicit forfeited its right to assert a new antedating theory based on corrected inventorship.
Implicit argued that § 256 contains no temporal limitation and that corrections operate retroactively, requiring the Board to revisit its unpatentability determinations once Carpenter was added as an inventor. Sonos and the USPTO countered that Implicit had litigated the IPRs on a single inventorship theory and waited until after adverse final written decisions to change course.
The Federal Circuit affirmed on both grounds.
First, the Federal Circuit found that forfeiture principles may apply notwithstanding the retroactive effect of § 256. Although corrections of inventorship generally operate retroactively, the statute does not shield a party from the procedural consequences of failing to timely raise arguments in an adjudicatory proceeding. Where inventorship bears directly on issues such as priority or antedating, diligence in asserting relevant theories is required.
Second, applying an abuse of discretion standard, the Federal Circuit concluded that the Board reasonably found forfeiture. Implicit possessed the relevant inventorship facts from the outset but chose to litigate the IPRs solely on the theory that Balassanian and Bradley were the only inventors. It did not advance any alternative inventorship based antedating theory during the IPR proceedings. Only after receiving adverse final written decisions did Implicit seek to add Carpenter and reframe its antedating position.
The Federal Circuit distinguished Egenera v. Cisco Systems where a mid litigation inventorship correction was permitted following a change in claim construction that altered the inventorship analysis. Here, by contrast, no intervening change in claim scope or law justified revisiting inventorship. Allowing Implicit to do so would have rewarded strategic delay and undermined the orderly conduct of IPR proceedings.
Practice note: The decision underscores the importance of raising all plausible inventorship and antedating theories during IPR proceedings. Although § 256 permits correction of inventorship with no express time limit, a late stage correction will not revive arguments that could have been presented earlier. Patent owners should carefully assess inventorship and priority issues at the outset of an IPR and avoid relying on post hoc corrections to salvage an unsuccessful litigation strategy.
