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• Stylized Looks
• BxDFs
  • Lama.  Lama is not yet available for XPU
  • PxrSurface is supported, but there are a few edge cases that are not.
    • subsurfaceSubset is not supported
• Color Management
  
  • XPU does not support color temperature on lights yet, so we cannot apply the right color space when converting a temperature to an RGB value
• Geometry
  • Facesets.  Facesets for shading are not supported.
  • Loop Subdivision.  Catmull-Clark is supported
  • Points.  Have been partially implemented.  Point falloff is not yet supported.
  • NURBS
  • Quadrics
  • Blobbies
  • The built-in curvature doesn't match RIS and will be receiving enhancements in a future release
  • Nested instancing
• Ray Tracing
  
  • Motion blur has not been fully implemented
  • Trace Subsets have not been implemented.  This then impacts the subsurfaceSubset feature of PxrSurface
• Textures
  • Dynamic path construction in your own patterns is not supported, but please note that we do support the following path tokens <UDIM>, <u>, <v>, <U>, <V> and <primstr:varname> that will result in a "dynamic" path to your textures.  <primstr:varname> can be used to reference the value in a constant primvar or user attribute to build a dynamic path.  Also note that <primstr:varname> is not in beta1 for XPU, but will be in a later beta.
  • XPU samples textures at one MIP level coarser than RIS so that it may store more textures in limited GPU memory.  This results in slightly blurrier renders from XPU than RIS.
• Patterns
  • Dynamic String construction in your own patterns is not supported
  • PxrSeExpr not supported
  • trace() OSL call is not yet supported.  In the future when it is implemented, it will only support one level of recursion.
  • Point clouds not supported
  • PxrBakeTexture and PxrBakePointCloud not supported
  • Transformations between color spaces spaces are ignored
• Lighting
  • Light Filters
  • Light Linking
  • "shot" oriented Lighting features.  Examples include:
    
    • Visible in Refraction Paths
    • Emission Focus
    • Light groups
    • Manifold Next Event Estimation
  • Thin shadows
  • Mesh lights
  • Color temperature
  • Cylinder Light
  • PxrEnvDaylight
  • Large numbers of lights.  XPU does not have a light selection scheme that allows it to scale to large number of lights.
• Volumes
• User defined AOVs or LPEs
  • Only some geometric built-in AOVs are available under the same name they are available for RIS.
• Integrator restrictions
  • numBxdfSamples, numLightSamples, numIndirectSamples (and their manually set counterparts)
  • clampDepth and clampLuminance have not been implemented as a way to supress fireflies
  • Russian Roulette has not been implemented
  • allowCaustics is always 1
• Adaptive sampling
• Baking - either at the pattern level via PxrBakeTexture or at the renderer level to bake global illumination
• Object attributes
  • maxdiffusedepth
  • maxspeculardepth
• The built-in curvature calculation different is different to RIS, which results in differences in specular mollification.
• GPU required, even if all you are doing is CPU rendering
• Thread count limits on startup not respected
• Display filters
• Sample filters (which means that Cryptomatte is not yet supported)
• The "weighted" option for the pixelfiltermode parameter to the Hider
• Procedurals not supported.  However, if you are using the latest XGen in Maya, you should get renders of your data.
• Image output - only EXR and TIFF
• Plugins for Custom OSL Patterns are supported, other plugin types are not (including BxDFs, Integrators, RtxPlugin for dynamic textures, Sample Filters, Display Filters, Lights, Light Filters, etc).
• Holdouts, shadow collectors
• Deep Output
• Multi-camera, multi-frame
• PxrOcclusion, PxrVisualizer, PxrUnified
• macOS not supported.

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