Adopted in 2010, Criminal Rule 16(K) mandates that the parties disclose their expert-witness reports at least 21 days before trial. If the 21-day rule is violated, the remedy at trial is exclusion to the extent there was non-compliance, a mandatory remedy reinforced and emphasized by the Ohio Supreme Court when it addressed the rule in State v. Boaston, 160 Ohio St.3d 46, 2020-Ohio-1061.