Even manually building Bullet, it never installs that file, which leads me to believe it should be an internal-only file, and should not be used by external projects. The btBulletWorldImporter.h file and btBulletWorldImporter class don’t even show up in the Bullet API docs. If it should be externally accessible, we’ll need to talk to the Bullet team and get it changed upstream; otherwise, we really should be sticking to what’s available in their public API, or this won’t work at all on Linux systems without getting the source.