November 2019 saw the beta launch of a shared open access repository service for UK cultural heritage organisations. This platform brings together research outputs of national ‘GLAM’ sector organisations in receipt of Arts and Humanities Research Council (AHRC) funding. The service was borne out of funder mandates for opening up research, in conjunction with a 2018 report from the Universities UK Open Access Repositories Working Group, which warned of the infrastructural and resource inefficiencies incurred where organisations have chosen to develop their own repositories independently. Coordinated by the British Library, the service has established a shared technical infrastructure and community of practice in open access for cultural heritage organisations. This paper will share the challenges faced, and benefits realised, during the first four years of the service, demonstrating what - and how - the participating institutions have gained from this close relationship, rather than going it alone.