Many believe that, by creating new incentives and accountability for providers (eg, physicians, clinics, and hospitals), accountable care organizations (ACOs) can help us achieve the triple aim of better population health, better patient experience, and lower costs.1 Although private payers are supporting ACO formation, the Centers for Medicare & Medicaid Services ACO programs are the largest and most prominent. In fact, the Medicare Shared Savings Program (MSSP)—the largest of the federal ACO models—has already grown to include 404 participants covering more than 7.3 million Medicare beneficiaries.2 To date, initial evaluations of the MSSP model have identified moderate success in reducing costs, while meeting quality and patient-experience benchmarks.3,4 To achieve these goals, the earliest MSSP ACOs have focused on primary care, better care coordination, and reducing overutilization of heath care services.5