This paper studies the impact of employee output information disclosure through GitHub on labor reallocation towards large firms. GitHub, which is the world’s largest software management platform, tracks and publicly displays real-time individual contributions. In 2016, a policy change enabled GitHub users to display their contributions more accurately on their profiles. Following this update, employees with 1 standard deviation higher GitHub contributions witnessed a 5.7% increase in job transitions to large firms, predominantly at the expense of smaller companies. While productive individuals left small firms for senior roles in larger companies, the latter retained them through internal promotions. The departure of productive workers led to an overall reduction in employment growth and productivity for small firms with more productive employees prior to the shock. Our findings highlight the role of labor-related big data in amplifying the dominance of large firms in recent years.