This article provides an attempt to better understand the establishment of international knowledge relationships, including changes over time. Internationalization of young high-tech firms is strongly required given the drive for upscaling technology solutions and given the increased global spread of knowledge centers. To increase understanding, a framework of conditions of capability formation in internationalization is developed and measured using a sample of 105 university spin-off firms in Northwest Europe. In early years, 62 per cent of these firms employed knowledge relationships abroad, often crossing continents. The main capabilities in this stage tend to be connected to education (PhD) and market training, innovation activity at practical level, and diversity in preceding domestic networks. Subsequent changes on the firm level show a somewhat stronger internationalization, 74 per cent, associated with other capabilities compared to early years, mainly derived in previous internationalization, pre-start work experience and innovation activity at an advanced level. However, the results also point to a 'problematic' segment of firms, including shrinking patterns and persistent absence of internationalization. To summarize, we observe inertia as well as (highly) dynamic patterns of knowledge relationships abroad, with important implications for management and policy.