Redshift provides a robust feature set such as volumetric rendering, hair rendering, tessellation and displacement, dedicated skin shader, etc. Furthermore, it has a variety of viewports and render denoisers, including the powerful OIDN (CPU) and OptiX (GPU) denoisers. Therefore, Cycles is a pretty fast path tracer in addition to its outstanding feature set. Its support for OptiX-based rendering allows Cycles to significantly boost render speeds by using RTX cores. Besides, Cycles is able to take advantage of CUDA or OptiX-powered rendering from certain graphics cards. To name a few features, powerful PBR shading nodes, accurate subsurface-scattering, vector displacement and adaptive subdivision, volume scattering, and absorption, caustics, cryptomatte support, etc. You can find more information on supported features and known limitations as well as hardware and drive requirements for Arnold GPU on the Arnold documentation portal.Cycles has a wide array of rendering features. Note that at this time, there are still some limitations to rendering with Arnold GPU. The majority of lights are supported, including portals.Most LPEs (39/46 and counting) are now supported.GPU noise is now on par with CPU noise when using adaptive sampling, which has been improved to yield even faster, more predictable results regardless of the renderer used. Excessive sources of noise have been removed, such as indirect noise in refractions or reflections.A first version of the new Shadow Matte shader has been added to the GPU renderer.Bounding volume hierarchy (BVH) memory used by geometry is reduced by as much as 50% for large meshes.Time to first pixel is now faster thanks to a number of improvements including more efficient NVIDIA OptiX caching.Textures are now loaded on-demand instead of at the start of the render, helping to reduce memory usage and save time from the first pixel.Improved support for Open Shading Language (OSL).Arnold 6 now rounds out the Arnold GPU toolset with updates across lights, shaders, and cameras:

We first unveiled Arnold GPU as a beta release in March 2019 with support for a set number of features, including shading networks, hair, SSS, atmospherics, instancing, and procedurals.

Autodesk arnold render