Motion vector mode.
Unity configures the following built-in shader uniforms to calculate motion vectors in HLSL code: unity_MotionVectorsParams, unity_MatrixPreviousM and unity_MatrixPreviousMI.
For Mesh ray tracing instances, unity_MotionVectorsParams is a vector uniform. Its component values are as follows:
unity_MatrixPreviousM and unity_MatrixPreviousMI are the instance matrix and its inverse respectively used in the previous frame. Note that Unity only updates these matrices only when there's a Camera in the Scene that's using the DepthTextureMode.MotionVectors flag in Camera.depthTextureMode.
To access the ray tracing instance matrix in closest hit, any hit, and intersection shaders, use the ObjectToWorld or WorldToObject HLSL functions.
Additional resources: MotionVectorGenerationMode.