A recent decision by the U.S. Court of Appeals for the Federal Circuit regarding the scope of estoppel triggered by an inter partes review (IPR) proceeding initially prompted panic among patent litigants, as it suggested a far broader scope of estoppel than had been applied under controlling precedent to that point. But a quick-on-its-feet Federal Circuit issued an errata opinion just over two weeks later, correcting certain of its statements regarding IPR estoppel. While the corrected opinion still overrules one prior decision—as was clearly intended based on the Federal Circuit's reasoning—the correction otherwise moved the decision back in line with precedent.

On Feb. 4, 2022, the Federal Circuit initially issued its opinion in California Inst. of Tech. v. Broadcom Ltd., 25 F.4th 976 (Fed. Cir. 2022) (Caltech), which raised concerns that the Federal Circuit was applying a far broader estoppel than it had before, preventing a patent challenger in an IPR proceeding from, in a parallel district court case, raising invalidity defenses against any patent claim in a challenged patent—even those claims that were not at issue in the IPR proceeding. But, later that month, the Federal Circuit issued an errata opinion clarifying that IPR estoppel applies only as to patent claims actually challenged in an IPR proceeding. That said, the corrected decision still overruled a prior decision of the Federal Circuit and provided clarity on the question of whether IPR estoppel applies to invalidity grounds that the challenger "reasonably could have raised" in the IPR.