Centers for Medicare and Medicaid Services (CMS) developed the ACO Investment Model (AIM) to encourage the growth of Accountable Care Organizations (ACOs) in rural and underserved areas. AIM provides financial support to eligible ACOs through pre-payment of shared savings. Abt’s study shows provider participation in AIM was associated with a differential reduction in total Medicare spending of $131 million. CMS made $76.2 million in pre-payments and paid an additional $6.2 million to ACOs whose shared savings exceeded their prepayments. After accounting for this spending, the aggregate net reduction was $48.6 million. Decreases in hospitalizations and use of institutional post-acute care contributed to the observed reduction in overall spending.