Informal Education for High-Performance Computing and Cross-National Collaboration with National Cometencence Centers and Centers of Excellence

High-Performance Computing (HPC) drives scientific and technological innovation, requiring a workforce capable of adapting to rapidly evolving tools and methodologies. While formal education provides foundational knowledge, informal learning-through workshops, hackathons, and targeted training-offers handson experience that accelerates skill development and bridges the gap between theory and practice. Cross-national collaboration plays a critical role in amplifying the effectiveness of informal education. Partnerships between institutions, National Competence Centers (NCCs), and Centers of Excellence (CoEs) foster knowledge exchange, resource sharing, and coordinated efforts to address complex challenges such as climate modeling and artificial intelligence. In particular, cooperation has significantly strengthened Slovenia's HPC ecosystem by broadening training access and enriching expertise. This paper explores how informal education and international collaboration support the development of HPC competencies, with a focus on NCC Slovenia's role within the EuroHPC framework. It presents data from 2023-2024 showing substantial growth in training activities, participation, and repeated attendance. The findings underscore the importance of collaborative, flexible learning models in building a skilled and resilient European HPC workforce.