37 C.F.R. § 42.108 : Patents, Trademarks, and Copyrights — UNITED STATES PATENT AND TRADEMARK OFFICE, DEPARTMENT OF COMMERCE — GENERAL PATENTS — TRIAL PRACTICE BEFORE THE PATENT TRIAL AND APPEAL BOARD — INTER PARTES REVIEW —INSTITUTING INTER PARTES REVIEW — Institution of inter partes review

(a) When instituting inter partes review, the Board will authorize the review to proceed on all of the challenged claims and on all grounds of unpatentability asserted for each claim.
(b) At any time prior to a decision on institution of inter partes review, the Board may deny all grounds for unpatentability for all of the challenged claims. Denial of all grounds is a Board decision not to institute inter partes review.
(c) Inter partes review shall not be instituted unless the Board decides that the information presented in the petition demonstrates that there is a reasonable likelihood that at least one of the claims challenged in the petition is unpatentable. The Board's decision will take into account a patent owner preliminary response where such a response is filed, including any testimonial evidence. A petitioner may seek leave to file a reply to the preliminary response in accordance with §§ 42.23 and 42.24(c). Any such request must make a showing of good cause.

37 C.F.R. §42.108

77 FR 48727, 8/14/2012, as amended at 81 FR 18766, 4/1/2016; 85 FR 79129, 1/8/2021