Background In 2016, the California Department of Healthcare Services (DHCS) released an “All Plan Letter” (APL 16-014) to its Medicaid managed care plans (MCPs) providing guidance on implementing tobacco-cessation coverage among Medicaid beneficiaries. However, implementation remains poor. We apply the Exploration, Preparation, Implementation, Sustainment (EPIS) framework to identify barriers and facilitators to fidelity to APL 16-014 across California Medicaid MCPs. Methods We assessed fidelity through semi-structured interviews with MCP health educators ( N = 24). Interviews were recorded, transcribed, and reviewed to develop initial themes regarding barriers and facilitators to implementation. Initial thematic summaries were discussed and mapped onto EPIS constructs. Results The APL (Innovation) was described as lacking clarity and specificity in its guidelines, hindering implementation. Related to the Inner Context, MCPs described the APL as beyond the scope of their resources, pointing to their own lack of educational materials, human resources, and poor technological infrastructure as implementation barriers. In the Outer Context, MCPs identified a lack of incentives for providers and beneficiaries to offer and participate in tobacco-cessation programs, respectively. A lack of communication, educational materials, and training resources between the state and MCPs (missing Bridging Factors) were barriers to preventing MCPs from identifying smoking rates or gauging success of tobacco-cessation efforts. Facilitators included several MCPs collaborating with each other and using external resources to promote tobacco cessation. Additionally, a few MCPs used fidelity monitoring staff as Bridging Factors to facilitate provider training, track providers’ identification of smokers, and follow-up with beneficiaries participating in tobacco-cessation programs. Conclusions The release of the evidence-based APL 16-014 by California's DHCS was an important step forward in promoting tobacco-cessation services for Medicaid MCP beneficiaries. Improved communication on implementation in different environments and improved Bridging Factors such as incentives for providers and patients are needed to fully realize policy goals. Plan Language Summary In 2016, the California Department of Healthcare Services (DHCS) in California released an “All Plan Letter” (APL 16-014) to its Medicaid managed care plans (MCPs) providing guidance on implementing tobacco-cessation coverage to address tobacco use among Medicaid beneficiaries. We conducted semi-structured interviews with health educators in California Medicaid MCPs to explore the barriers and facilitators to implementing the APL using the Exploration, Preparation, Implementation, Sustainment framework. According to MCPs, barriers included a lack of clarity in the APL guidelines; a lack of resources, including educational materials, infrastructure to identify smokers, and human resources; and a lack of incentives or penalties for providers to provide tobacco-cessation materials to beneficiaries. Facilitators included collaboration between MCPs and state and/or national public health programs. Overall, our findings can provide avenues for improving the implementation of tobacco-cessation services within Medicaid MCPs.