Sony Imageworks’ implementation of the Arnold renderer is a fork of the commercial product of the same name, which has evolved independently since around 2009. This article focuses on the design choices that are unique to this version and have tailored the renderer to the specific requirements of film rendering at our studio. We detail our approach to subdivision surface tessellation, hair rendering, sampling, and variance reduction techniques, as well as a description of our open source texturing and shading language components. We also discuss some ideas we once implemented but have since discarded to highlight the evolution of the software over the years.