Cost transparency for transformative agreements (or how to calculate equivalent APCs within the DEAL-Wiley agreement)

So far, OpenAPC has recorded cost data on Open Access articles in gold OA and hybrid journals. In view of the complexity of cost models for institutions participating in transformation contracts and the scope of costs for institutions with high subscriptions and, in the future, for institutions with high publication volumes, the question arises as to how the institutional costs per OA article in hybrid journals can be reported transparently in the context of transformation contracts. In addition, transformation agreements with large publishers concern relevant quantities of journal articles. For example, the DEAL-Wiley treaty covers about 12% of the annual German publication output in scientific journals.
As part of the DFG-funded "INTACT" project, OpenAPC has already gained experience in monitoring OA articles in hybrid journals from transformative contracts (Springer Compact). In the context of the current BMBF-funded project "Cost Transparency as a Contribution to Open Access Transformation - KOA", we would like to work together with the data-giving OpenAPC community in this workshop to develop a procedure for the recording and cost-transparent presentation of article-related costs from transformation contracts using the DEAL-Wiley contract as an example.