Moscot introduces three key innovations that unlock the full power of OT. First, it supports multimodal data across all models. Second, it overcomes previous scalability limitations to enable atlas-scale applications. Third, moscot is a unified framework with a consistent API across biological problems, which will facilitate usability and enable extensions to new problems in a straightforward manner. Panels a and b were created using BioRender ( https://www.biorender.com ).