(Also if I understand correctly) there are two kinds of batches here - the instances and the path segments (or path "depth"). Path segment batches are the outer

(Also if I understand correctly) there are two kinds of batches here - the instances and the path segments (or path "depth"). Path segment batches are the outer loop, and instance batches are the inner loop. So in terms of path tracing, the instances being batched is a detail that is hidden from the rendering algorithm. Each launch (or batch of instances) performs partial updates to the render buffers (tmax, normal, etc.), until all the instances have been processed, and then the tracing of the next path segment begins, which loops through the instance batches again.