Objective: To evaluate the impacts of a transition to an "integrated managed care" model, wherein Medicaid managed care organizations moved from a "carve-out" model to a "carve-in" model integrating the financing of behavioral and physical health care.Data Sources/Study Setting: Medicaid claims data from Washington State, 2014-2019, supplemented with structured interviews with key stakeholders.Study Design: This mixed-methods study used difference-in-differences models to compare changes in two counties that transitioned to financial integration in 2016 to 10 comparison counties maintaining carve-out models, combined with qualitative analyses of 15 key informant interviews. Quantitative outcomes included binary measures of access to outpatient mental health care, primary care, the emergency department (ED), and inpatient care for mental health conditions. Data Collection: Medicaid claims were collected administratively, and interviews were recorded, transcribed, and analyzed using a thematic analysis approach.