Inter partes review, created by the America Invents Act, is a proceeding before the PTAB in which a petitioner challenges one or more claims of an issued patent as anticipated or obvious in light of prior art patents or printed publications. It offers a faster, generally less expensive alternative or complement to litigating invalidity in district court.

A petitioner files a petition, the Board decides whether to institute review, and if instituted, a final written decision issues on a statutory timeline. Discovery is far more limited than in district court litigation. Once a final written decision issues, the petitioner is estopped from later raising, in district court or before the PTAB, any invalidity ground it actually raised or reasonably could have raised in the IPR.

Within a simulation, a pending IPR is naturally modeled as a parallel branch that can pause or reshape the district court timeline: a user can toggle whether a stay is granted and see how the case tree, cost, and estoppel exposure shift depending on how and when the PTAB proceeding resolves.

Defendants accused of patent infringement often file an IPR petition alongside or shortly after being sued, both to challenge validity on a faster, cheaper track and to seek a stay of the parallel district court case. Because of the estoppel effect, parties weigh which invalidity grounds to raise in the IPR carefully, since grounds not raised there may later be foreclosed only for grounds reasonably available at the time.