<p>Open source software (OSS) has established itself as an integral part of modern software development and is also becoming increasingly important in the startup context. This study analyses the OSS activities of German unicorns using a quantitative content analysis of their public Git repositories. The aim is to identify correlations between OSS activities and company success. The results show that almost all of the companies analysed operate public Git repositories. However, there is also an asymmetrical distribution of OSS activities, with a few companies being very active, while the majority have a comparatively low level of activity. An Open Source Activity Index (OSAI) enables a standardised comparison of companies with regard to their OSS activities. The data indicate that although open source is an important strategic instrument in the German unicorn ecosystem, the success of companies depends on a variety of other factors and is not primarily determined by the intensity of OSS activities. The study contributes to research in the field of digital entrepreneurship and provides practical implications for startup founders, investors and policy makers regarding the strategic use of open source to foster innovation.</p>