An IPR petitioner may, by request, and at the PTAB’s discretion, join another party’s prior filed IPR [1]. A petitioner may seek to join an IPR to avoid the bar to filing more than one year after service of a complaint alleging infringement or to ensure the petitioner can continue its IPR if the parties to the prior filed IPR settle. If the petitioner’s challenge is substantially the same as that in the earlier IPR, it weighs in favor of joinder [2]. Parties often copy the petitions from prior filed IPRs to facilitate joinder.

What happens if a petitioner knows of additional prior art references not asserted in the prior filed IPR? The petitioner may notice the strategic opportunity to sit on those references, join the prior filed IPR, wait to see how the patent owner and Board react and then file a second IPR using the new references before a final written decision triggers estoppel. The PTAB addressed such possible gamesmanship in International Business Machines Corp. v. Zitovault, LLC [3].

The petition at issue was IBM’s second petition against the same patent. IBM’s first petition asserted the same prior art references as an instituted IPR Amazon filed. The Board allowed IBM to join that Amazon IPR. Later, after having the benefit of seeing the patent owner’s response, IBM filed a second IPR petition challenging the same claims (plus one additional claim) using new references. IBM had been aware of these references before filing its first petition.

Considering the delay in asserting the new references, the Board in its discretion declined to institute IBM’s second IPR. It cited several factors that address the potential strategic advantage a petitioner may gain when it files two petitions against the same patent. The factors included whether the petitions were directed to the same claims, whether the petitioner knew of the later asserted prior art when it filed its first petition, whether the petitioner had already received the patent owner’s preliminary response and the Board’s institution decision when it filed the second petition, how long the petitioner withheld the prior art before filing the second petition and the adequacy of the petitioner’s explanation for the delay between petitions.

The Board found the factors supported denying institution. IBM’s first petition challenged nearly all the same claims as the second, it had known of the new references, and its only excuse for the substantial delays in filing the second petition was that it wanted to join the Amazon IPR. However, nothing prevented IBM from either foregoing joinder and filing one petition asserting all grounds or filing two petitions simultaneously. Instead, IBM waited until it had the benefit of the patent owner’s response in, for example, addressing a disputed claim construction. The Board declined to give IBM this advantage.


The Board’s decision here should encourage practitioners to include all known references they intend to assert against a patent in their first IPR petition or in multiple petitions filed simultaneously. If an IPR has already been filed against the target patent, the petitioner may choose to wait to see how issues are addressed in that proceeding. However, once the petitioner files its own IPR, it should not sit on any grounds until a future date.