This study examines how academic libraries in the UK responded to the Research Excellence Framework (REF) 2021 open access policy. Thirteen information professionals at twelve institutions across the UK took part in semi-structured interviews. Findings from the interviews reveal how libraries created and deployed new infrastructures, workflows, and staffing as well as the methods through which universities communicated the policy's requirements. The study describes respondents' experiences of the changes brought about by REF 2021 as well as their thoughts on how the REF 2021 open access policy will affect future REF assessments. Results provide insight for libraries responding to US initiatives such as the August 2022 White House Office of Science and Technology Policy memo directing the open publishing of federally funded research.