In this session, we share insights from a large-scale migration project for a major client in the automotive industry, involving over 300 developers. We migrated more than 150 COBOL projects from a long-standing, proprietary source code management system on z/OS to Git. Key challenges included integrating the legacy build system, migrating a custom versioning scheme, detecting non-printable characters in legacy code, restructuring the monolithic codebase into clean, independent repositories and onboarding the development teams for the new Git workflow. We leveraged IBM Dependency Based Build and integrated zAppBuild as an open-source build framework. This session highlights practical solutions, pitfalls, and lessons learned.