For more context here is a minimal RealityKit view to reproduce the test setup. var body: some View { RealityView { content in let material = SimpleMaterial(color: .systemPink, isMetallic: false) let mesh = MeshResource.generateSphere(radius: 1) // MeshResource.generateSphere creates a model with this name let model0 = mesh.contents.instances["MeshModel-0"] let modelName = model0!.model // This implementation tries to create a new MeshResource vs MeshResource.replace() var instances: [MeshResource.Instance] = [] let instanceCount = 20 for i in 1...instanceCount { let translation: SIMD3<Float> = [Float.random(in: 0...1), Float.random(in: 0...1), Float.random(in: 0...1)] // Nothing in the docuementation indicates what the id needs to be. let instance = MeshResource.Instance( id: "MeshModel-\(i)", model: modelName, at: Transform( scale: [0.05, 0.05, 0.05], translation: translation).matrix) instances.append(instance) } var contents = MeshResource.Contents() contents.models = mesh.contents.models contents.instances = MeshInstanceCollection(instances) do { let finalMesh = try await MeshResource(from: contents) var spheres = ModelEntity(mesh: finalMesh, materials: [material]) content.add(spheres) } catch { print("failed to create mesh resource \(error.localizedDescription)") } } } Here is a screenshot of the RealityKit trace. Maybe there is some specific requirements on a usdz file that will trigger RealityKit to used instanced rendering.