MuJoCo 3.16 adds robot-model scaling while preserving the physics

What changed

MuJoCo 3.16 adds compile-time scaling for frames. Model authors can use the new scale, scaling and massscale attributes to resize components without rewriting the underlying specification. The compiler also updates references such as actuators, tendons, constraints, sensors, keyframes and mesh assets so related parts stay aligned.

The default “similar” policy scales physical quantities together so dynamics are preserved when gravity is scaled proportionally. A “geometry” policy changes spatial dimensions and inertias, supports anisotropic scaling and lets modelers choose how mass should change. The release also adds initial Bazel build support for the core library, viewer, plugins and samples.

Why robotics builders will notice

For robotics teams, this reduces a painful iteration loop: a model can be adapted at compile time while preserving its original authoring coordinates. It is a simulation-tool change, not a new robot capability by itself. The same release also has breaking API changes, so existing plugin authors should read the migration notes before upgrading.