Abstract: Wellcome, UK Research and Innovation, and the Association of Learned and Professional Society Publishers commissioned Information Power Ltd. to undertake a project to support society publishers to accelerate their transition to open access (OA) in alignment with Plan S and the wider move to accelerate immediate OA. This project is part of a range of activities that cOAlition S partners are taking forward to support the implementation of Plan S principles. The objective of this project was to explore with learned societies a range of potential strategies and business models through which they could adapt and thrive under Plan S. We consulted with society publishers through interviews, surveys, and workshops about the 27 business models and strategies identified during the project. We also surveyed library consortia about their willingness to support society publishers to make the transition to OA. Our key finding is that transformative agreements emerge as the most promising model because they offer a predictable, steady funding stream. We also facilitated pilot transformative agreement negotiations between several society publishers and library consortia. These pilots and a workshop of consortium representatives and society publishers informed the development of an OA transformative agreement toolkit. Our conclusion is that society publishers should consider all the business models this project has developed and should not automatically equate OA with article publication charges.