This action finalizes the Environmental Protection Agency's (EPA) determination that the existing Cross-State Air Pollution Rule Update for the 2008 Ozone National Ambient Air Quality Standards (NAAQS) (CSAPR Update) fully addresses certain states' obligations under the good neighbor provision of the Clean Air Act (CAA) regarding interstate pollution transport for the 2008 ozone NAAQS. The CSAPR Update, published on October 26, 2016, promulgated Federal Implementation Plans (FIPs) for 22 states in the eastern U.S. In the final CSAPR Update, based on information available at that time, the EPA could not conclude that the rule fully addressed these CAA section obligations for 21 of the 22 CSAPR Update states. As a result, the EPA has an outstanding obligation to fully address the requirements of this Clean Air Act provision for these states. Based on information and analysis that became available after the CSAPR Update was finalized, this action finalizes a determination that the existing CSAPR Update fully addresses the CAA's good neighbor provision for the 2008 ozone NAAQS for all remaining CSAPR Update states. Specifically, EPA is finalizing a determination that 2023 is an appropriate future analytic year to evaluate remaining good neighbor obligations and that, for the purposes of addressing good neighbor obligations, there will be no remaining nonattainment or maintenance receptors with respect to the 2008 ozone NAAQS in the eastern U.S. in that year. Therefore, with the CSAPR Update fully implemented, these remaining CSAPR Update states are not expected to contribute significantly to nonattainment in, or interfere with maintenance of, any other state with regard to the 2008 ozone NAAQS. In accord with this finding, the EPA has no outstanding, unfulfilled obligation to establish additional requirements for emission sources in these states to further reduce transported ozone pollution under the good neighbor provision for the 2008 ozone NAAQS. As a result of this