37 CFR § 42.208 - Institution of post-grant review.
(a) When instituting post-grant 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 institution of post-grant 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 post-grant review.
(c) Post-grant review shall not be instituted unless the Board decides that the information presented in the petition demonstrates that it is more likely than not 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.