Rheinmetall publishes onboardapi — but only the interface spec is open

Rheinmetall has released documentation for onboardapi, a middleware library that standardizes how sensor systems and software components exchange data across mixed hardware and software environments. It’s built on the company’s ddkit SDK and rides on the Object Management Group’s Data Distribution Service (DDS), a data-centric publish-subscribe standard aimed at reliable, low-latency messaging. The design leans on DDS XTypes and XCDR2 encoding so that different versions of a deployment can keep interoperating as the underlying data model changes. The core ships in C++, with wrappers exposing the API to Java, C#/.NET, and Python.

The “open-sources” framing overstates what’s actually on offer. Only the interface descriptions carry an open license (Eclipse Public License v2.0); the runtime libraries that make the thing work remain under a proprietary end-user agreement, EULA-RME-SDK-1.0. In practice that means outside parties can read and build against the published data model and interfaces, but they don’t get freely licensed, buildable source for the running components — closer to an open specification than open-source software.

The significance is less about the code and more about the source: a major European defense contractor publishing an interoperability contract for connected battlefield systems. Standardizing the data plane lowers the integration cost for third parties building sensors or software that plug into Rheinmetall’s stack, while the split licensing lets the company court an ecosystem without surrendering its core IP. Note that the documentation itself describes only generic sensor-to-software middleware — the “Battlesuite connected weapon system” and weapons context come from the headline, not the published material.