Interference Estoppel Reviewability Shenanigans? The Federal Circuit Thinks Not

In IGT v. Zynga Inc., No. 2023-2262 (Fed. Cir. July 22, 2025) the Federal Circuit affirmed the PTAB’s final written decision invalidating the subject claims as obvious. Underlying this decision was the court’s holding that the PTAB’s declination to apply “interference estoppel” was unreviewable.

In 2010, interference proceedings were declared based on IGT’s patent and Zynga’s patent application. Zynga argued IGT’s claims were unpatentable for obviousness; however, the Board terminated the proceedings after finding Zynga’s claims were not supported by the written description of its application. In 2021, Zynga petitioned the Board to institute IPR proceedings against the same IGT patent alleging obviousness of the claims. IGT argued interference estoppel barred Zynga from raising the obviousness challenge under 37 C.F.R. § 41.127(a)(1). Both the Board and the Director rejected the IGT’s argument, and ultimately the Board concluded all challenged claims were unpatentable.

On appeal, the Court found the Board’s refusal to apply interference estoppel was tantamount to appealing an institution decision, which is unreviewable. Moreover, the Court considered two grounds provided by the Board and the Director for not applying interference estoppel sufficient to hold the PTO did not engage in “shenanigans not in accordance with law.”