ABSTRACT Health inequities in older adults along racial and sociodemographic lines are persistent and pervasive in the United States. These inequities are particularly profound among older adults living with Alzheimer’s Disease (AD) and AD-related dementias (ADRD). One way to improve outcomes and equity in Medicare is by moving beneficiaries into accountable care organizations (ACOs), in which groups of clinicians assume responsibility for quality and costs of care for patient populations on an annual basis. In 2023, the ACO Realizing Equity, Access, and Community Health (ACO REACH) program was launched. This new program differs from Medicare’s current ACO program (the Medicare Shared Savings program, or MSSP) in that it includes features and considerations specifically aimed at reducing health inequities among Medicare beneficiaries, including people from minoritized racial and ethnic groups and those living in poverty. Quantifying the impact of ACO REACH is critically important as Medicare and other payers increasingly shift towards ACO programs. Our overarching goal in this proposal is to determine if REACH improves equity and outcomes, overall and among beneficiaries with AD/ADRD, compared to Medicare’s current ACO program (the Medicare Shared Savings program, or MSSP) or to beneficiaries not enrolled in an ACO program. We also hope to understand the specific care redesign strategies ACOs undertake that might have particularly beneficial effects for health equity, using an implementation science lens to explore these in detail. Our specific aims are as follows: • Aim 1: Compare REACH ACOs to MSSP ACOs and non-participants on beneficiary, practice, and organization-level characteristics over time to determine whether REACH is achieving its goal of enrolling practice groups that care for high-risk beneficiaries. • Aim 2: Use innovative within-beneficiary analyses to determine if REACH is associated with improvements in quality, outcomes, and equity, overall and among beneficiaries with AD/ADRD. • Aim 3: Use an implementation science framework and a series of longitudinal interviews to characterize REACH leaders’ decision-making around program participation, practice engagement, quality improvement, and health equity, overall and for beneficiaries with AD/ADRD. This work will provide timely information to inform ongoing updates to ACO REACH, and ways in which its implementation could be further optimized for patients with AD/ADRD. This could help to maximize the likelihood that ACO REACH and future programs will have meaningful positive impact on equity for underserved populations.