The "Securing the Open Source Software Ecosystem: OS3I End of Year Report" focuses on the Open-Source Software Security Initiative (OS3I) efforts in 2023. Following the discovery of the Log4Shell vulnerability in 2021, the initiative, under the Biden-Harris Administration, aimed to enhance open-source software security. Key areas of focus included unifying the government's approach to software security, establishing strategic use of open-source software, promoting long-term security investment, and building trust within the open-source community. The report outlines the progress and future prospects of OS3I in strengthening the open-source ecosystem.