A path-breaking example of the interplay between geriatrics and learning healthcare systems is the Veterans Health Administration's (VHA's) planned roll-out of a program for providing participant-directed home- and community-based services to veterans with cognitive and functional limitations. We describe the design of a large-scale, stepped-wedge, cluster-randomized trial of the Veteran-Directed Home- and Community-Based Services (VD-HCBS) program. From March 2017 through December 2019, up to 77 Veterans Affairs Medical Centers will be randomized to times to begin offering VD-HCBS to veterans at risk of nursing home placement. Services will be provided to community-dwelling participants with support from Aging and Disability Network Agencies. The VHA Partnered Evidence-based Policy Resource Center (PEPReC) is coordinating the evaluation, which includes collaboration from operational stakeholders from the VHA and Administration for Community Living and interdisciplinary researchers from the Center of Innovation in Long-Term Services and Supports and the Center for Health Services Research in Primary Care. For older veterans with functional limitations who are eligible for VD-HCBS, we will evaluate health outcomes (hospitalizations, emergency department visits, nursing home admissions, days at home) and healthcare costs associated with VD-HCBS availability. Learning healthcare systems facilitate diffusion of innovation while enabling rigorous evaluation of effects on patient outcomes. The VHA's randomized rollout of VD-HCBS to veterans at risk of nursing home placement is an example of how to achieve these goals simultaneously. PEPReC's experience designing an evaluation with researchers and operations stakeholders may serve as a framework for others seeking to develop rapid, rigorous, large-scale evaluations of delivery system innovations targeted to older adults.