In April 2025 BWI, the Bundeswehr’s primary digitalisation partner, concluded a framework agreement with ZenDiS, with an initial term of seven years, covering the provision and further development of the open-source collaboration suite openDesk. Agreements of this kind are usually discussed in terms of sovereignty, cost or freedom from a dominant vendor. Open-source licensing can indeed widen a public buyer’s options, because it allows software to be inspected, modified, integrated on infrastructure the buyer controls and maintained by more than one supplier. A licence, however, does not supply the labour needed to exercise those options. A defence customer may hold source-code access, a long support agreement and an accountable systems integrator, while the engineers who understand a critical shared component sit outside that contractual relationship altogether. The financial question is therefore narrower than whether open source is cheaper or more sovereign than proprietary software. It is whether the money that supports a defence-facing digital service reaches, directly or indirectly, the technical functions needed to keep its shared software dependencies usable for the life of the service, and whether the capacity it buys can be distinguished from a licence right, an integration service, a temporary engineering project or a promise of customer support.