Mission software can be a perfect fit on day one, but become a liability over time. When critical capabilities depend on a single proprietary vendor, modernization is constrained, and security responses are jeopardized, as they depend entirely on how quickly that vendor discloses and patches vulnerabilities.This session will explore how open source software can reduce vendor lock by shifting control back to mission owners. We will discuss approaches that preserve the freedom to operate, modify, integrate, and maintain software independently of any one company, while still allowing commercial vendors to provide support and premium capabilities. Using Defense Unicorns’ open-core model as an example, we will examine how open foundations, government-friendly licensing, and eliminating technical “kill switches” such as expiring license keys can strengthen continuity of operations.Finally, we’ll look beyond simply consuming open source software to the importance of actively contributing upstream. Open ecosystems let government programs, integrators, and vendors fix critical issues, add capabilities, and share improvements rather than waiting on a single supplier. By designing systems for portability and software independence from the outset, the DOW can reduce modernization friction, improve resilience, and ensure mission owners retain meaningful control of the software their operations depend on.