Many payers, most notably the Centers for Medicare and Medicaid Services (CMS), have developed new payment models that base reimbursement on a broader bundle of services than traditional fee-for-service payment. The accountable care organization (ACO) program exemplifies the broadest of these new payment models. One of the crucial ACO design features is the extent to which providers are required to reimburse payers if spending exceeds a target, called the benchmark.