The EU-funded EUPEX will support the creation of a sustainable European scientific and industrial high-performance computing (HPC) ecosystem, and help lay the foundations for Europe’s digital sovereignty. Specifically, EUPEX will pave the way for the upcoming European Exascale systems. EUPEX will build a production-grade prototype that will be the EU’s first HPC platform integrating the full spectrum of European technologies, from architecture and processors to system software. The EUPEX prototype will be open and flexible thanks to its modular OpenSequana compliant platform and the corresponding HPC software ecosystem for the Modular Supercomputing Architecture. EUPEX’s ambition is also to prepare applications and users to efficiently exploit future European exascale supercomputers.