Open Sea Lab 4.0 Hackathon (OSL 4.0) unites data scientists, developers, and innovators to tackle key ocean challenges using EMODnet and Copernicus Marine data on the European Digital Twin Ocean (EDITO) platform. This edition emphasizes cross-thematic data fusion and real-time analysis within EDITO, supporting the EU Green Deal, the Mission Restore Our Ocean and Waters, and the UN SDGs. By leveraging EMODnet’s resources and DTO’s capabilities, OSL 4.0 fosters groundbreaking solutions for marine sustainability and innovation.