Open Defense APIs Can Still Leave One Vendor in Charge

Key takeaways

• An API’s value depends on what it exposes and the terms for using it.
• Shared interfaces can reduce integration work and make switching suppliers easier.
• Supporting the same API does not guarantee compatibility in operational conditions.
• Vendor control over updates and certification can preserve lock-in despite public documentation.

Buying drones, sensors, and command systems from different suppliers looks like a hedge against vendor lock-in. That hedge gets expensive if the equipment cannot exchange information. For Rheinmetall’s Battlesuite, the question is how much opening its Onboard API and Tactical API could change that equation.

Public documentation is a starting point

An API defines how software exchanges information: what it can request, what it receives, and how those messages are structured. In defense, those interfaces help support interoperability—the ability of different systems to work together.

Publishing an interface does not make the underlying product open source. Sample integration code does not necessarily give developers the right to modify the rest of the software, either.

A GitHub repository alone therefore says little about how much freedom a supplier or customer gains. The useful questions are concrete: Does it contain complete specifications, examples, or both? What do the usage terms permit?

Even the names “Onboard API” and “Tactical API” cannot establish which functions they support. That depends on the actual specifications.

Cheaper connections can expand the shopping list

Suppose one company’s sensor needs to send information to another company’s command system. If they use different data formats, someone has to build software that translates between them. Changes on either side may require more integration work.

A well-documented common API can reduce that burden. Developers can build against a defined interface without needing to untangle another supplier’s internal implementation.

For buyers, the potential benefit is supplier choice. They could replace a sensor while keeping the existing command system, instead of having one equipment change turn into a broader replacement project.

That freedom depends on the interface being useful enough. If essential functions remain unavailable through the public API, or every integration needs separate approval, the practical shopping list may still be short.

The relevant test is whether a competing supplier can deliver a working replacement on workable terms.

Matching messages can hide mismatched meanings

Two systems can speak the same API and still misunderstand each other.

Consider a status message that says “normal.” One device might mean that it has power. Another might mean that it has completed and passed its self-checks. A receiving system that treats those messages as equivalent could draw the wrong conclusion.

Compatibility testing must therefore go beyond checking whether a message arrives. Teams need to verify what the data means, when it updates, and what happens when a connection drops and returns.

Public specifications can supply information needed for that work. They cannot replace the work itself.

Reading an interface and trusting equipment to operate together are different milestones.

Control lives in the next version

The governance question is who gets to decide what changes next.

Having one company maintain a specification can have advantages. It can keep changes consistent and give customers a clear party to hold accountable when something breaks.

But if that company also controls every revision and compatibility certification, competing suppliers remain dependent on its decisions. They may have to keep adapting their products to its release schedule. Certification costs and conditions can also make participation harder.

Lock-in can shift from equipment purchases to updates and approvals. A buyer may gain the ability to choose another device while its supplier still needs the platform owner’s permission to keep that device supported.

That makes backward compatibility, outside participation, and independent testing central to the assessment. How long are older versions supported? Can other suppliers help improve the specification? Can compatibility be verified independently?

For Battlesuite, the clearest evidence of greater buyer freedom would be how easily customers can connect and replace competing equipment. Public interfaces could make that easier, but control over their evolution matters just as much. An open specification can still come with a gatekeeper.