Stereotypes about Millennials permeate conversations about public management, often without evidence. Based on generational theory and psychological contract theory, this study hypothesizes and empirically compares affective commitment levels of U.S. federal Millennials and Generation Xers. This study uses a time-lag design with data from the 2011 Federal Viewpoint Survey and the 2004 Federal Human Capital Survey to investigate Millennials and Generation Xers under 30 years old and untangle the generational difference effect while controlling for the age difference. The findings show that Millennials reported slightly higher levels of affective commitment in comparison with Generation Xers (contrary to common stereotypes). This study also reports null findings or the absence of evidence for the differences regarding how managerial practices (support for work–life balance, financial rewards, and meaningful work) influence their affective commitment. In addition, federal employees belonging to the Millennial generation reported work interests differing from the common stereotypes. This study advances public management scholarship regarding affective commitment of generations and young employees, as well as contributing evidence about generational differences in an under-studied field: the public sector. Practically, the findings help reduce erroneous stereotypes and foster effective and equitable management of the public workforce.