Germany is advancing its digital sovereignty with the Deutschland-Stack (D-Stack), a national reference architecture for AI and digital systems, designed to foster innovation and collaboration across federal, state, and municipal levels. Supported by the Federal Ministry for Digital Affairs and State Modernization, the D-Stack offers a platform of interoperable, open-source components to build secure and adaptable digital infrastructures. A key component is Haystack, an open-source framework by deepset, which enables the development of AI applications with a focus on trust, explainability, and data security, crucial for federal and defense environments. Haystack's modular design allows for flexible deployments, supporting everything from air-gapped defense systems to federated government architectures. The initiative emphasizes public participation and collaboration with the private sector to ensure the D-Stack remains a dynamic, evolving platform aligned with public values. This approach not only strengthens Germany's digital sovereignty but also sets a precedent for digital innovation and governance across Europe, positioning Haystack as a vital element in the future of sovereign AI systems.