An Inter Partes Review is a proceeding before the USPTO, which allows third parties to challenge the validity of the claims of an issued patent without going into federal court. This system replaced the prior inter partes reexamination proceeding in 2012.
The USPTO offers a great summary of interesting statistics on IPR’s and other proceedings before the PTAB (Patent Trial and Appeal Board). A few highlights: Institution rates have gone from about 87% in FY13 to about 56% in FY20. During that same time period, pre-institution settlements have remained about 9% to 12%, and post institution settlements have gone from 90% to only 20%. Of over twelve thousand petitions filed, only about thirty-four hundred have gone to final written decisions. Of the cases that were instituted but not settled, about 21% found all challenged claims unpatentable, and about 7% found all challenged claims patentable.