Worked on the stan-dev/stan repository to deliver a release-ready update by bumping the main project version to 2.39.0 and upgrading the Math Library subproject to v5.3.0-rc1. This effort focused on improving stability and compatibility for downstream users by aligning central references and tags across the codebase. The work was implemented through disciplined version control practices, ensuring clear traceability of changes. Leveraging C++ development skills and documentation expertise, the developer coordinated the subproject upgrade to support new library features. The approach emphasized careful library management and adherence to a structured release process, enhancing build and test consistency.