The Centers for Medicare & Medicaid Services today announced 121 new Medicare Accountable Care Organization participants, including 21 that will begin participating this year in a new Next Generation ACO model. The new model includes a prospectively (rather than retrospectively) set benchmark, allows beneficiaries to choose to be aligned to the ACO and tests beneficiary incentives for seeking care at participating providers. In addition, 39 ACOs will join two existing participants in the ACO Investment Model (AIM), which builds on the Advance Payment ACO model to encourage ACOs to form in rural and underserved areas and current Shared Savings Program ACOs to transition to arrangements with greater financial risk. The AIM model is expected to provide $83 million in upfront and ongoing investments to participants, which are repaid from the ACO’s earned shared savings. Today’s announcement brings the total number of Medicare ACOs to 477 across five models, including 100 new and 147 renewing SSPs and 64 ACOs in a risk-bearing track. Initiated in 2012, Medicare ACOs are groups of physicians, hospitals and other care providers who agree to coordinate care for patients and are held accountable for certain quality and performance measures.