Hyperion is Disney's physically based path tracer renderer. They present an overview of their results and a enjoyable 'Practical Guide to Path Tracing'.
Hyperion is a streaming ray-tracer, capable of performing multi-bounce GI on production-scale scenes without resorting to shading caches or instancing. To achieve this, we introduce a novel two-stage ray sorting framework. First, we sort large, potentially out-of-core ray batches to ensure coherence. Working with large batches is essential to extract coherent ray groups from complex scenes. Second, we sort ray hits for deferred shading with out-of-core textures. For each batch we achieve perfectly coherent shading with sequential texture reads, eliminating the need for a texture cache. Our approach is simple to implement and compatible with most scene traversal strategies.