HtoA 6.4.3.0

25 July 2025

HtoA 6.4.3.0 is a minor feature release using Arnold 7.4.3.0.

Arnold 7.4.3.0 is a feature release that includes a new Inference imager, performance improvements in Global Light Sampling and in GPU volumes, and other enhancements and bug fixes.

Installation

• Download Arnold for Houdini from your Autodesk Account. See Download Arnold for more information about downloading HtoA from your Autodesk Account.

• Follow these installation instructions

Enhancements

• Exposed per-AOV DeepEXR parameters on Arnold Render Settings (HTOA-2892):

  

• Faster rendering with Global Light Sampling: Scenes using Global Light Sampling, render up to 2.5x faster in our tests. The numbers below are for same-noise renders. (ARNOLD-13091)

• Improved Global Light Sampling (GLS) on glossy material in GPU renders: GPU renders (like CPU renders since Arnold 7.3.7.0) now take material glossiness into account when sampling, which greatly enhances the quality especially when many small lights are present. In the robot scene below, we get a ~3x speedup with adaptive rendering. (ARNOLD-15833)

7.4.2, fixed AA	7.4.3, fixed AA, GLS glossy enabled

• Faster volume rendering on GPU: Scenes with volumes (procedural or OpenVDB) render up to 3.3x faster in our tests. Scenes with OpenPBR transmission or scattering materials render up to 1.2x fasater. (ARNOLD-11077, ARNOLD-16304)

Instanced spheres - 1.18x faster	Byc cloud - 3.3x faster	Sunset clouds - 1.76x faster

• Inference Imager: The Inference imager is capable of performing inference on image-to-image machine learning models using the ONNX framework. (ARNOLD-16071)

• Improved thin-walled subsurface in OpenPBR: The OpenPBR subsurface lobe in the thin-walled mode uses subsurface_weight to blend between diffuse and subsurface lobes while maintaining energy conservation. You can use this, for example, to model diffuse transmission and reflection in paper. (ARNOLD-15982)

previous behavior
7.4.3
	0	0.01	0.5	1

• Energy conserving metal in OpenPBR: The OpenPBR metal lobe now conserves energy and passes the furnace test. (ARNOLD-16327)

previous behavior
7.4.3
	0.25	0.5	1

• Improved HTML reports: The Arnold Render Report now supports sorting of statistics, displays the stats of the final render only, and has improved styles for resizing charts and tables. (ARNOLD-15600, ARNOLD-16011, ARNOLD-16562)

• Renders automatically create output directories: Any time you render (for example, with kick or a DCC command-line process), the Arnold output drivers will automatically create any output folders that do not already exist. (ARNOLD-3476)

• Imager Optimizations: Imager framebuffer management has been improved to reduce overhead between imager chains. This is especially noticeable when handling many imager chains. For example, in a 4096 x 2160 resolution render, we see the overhead between imager execution reduced by 4x when compared to Arnold 7.4.2.2, saving about 1 second per imager chain. (ARNOLD-16261, ARNOLD-16264, ARNOLD-16281)

• Improved interactivity: Interactive render performance is improved, especially for camera moves and lighting changes. (ARNOLD-16200)

• CPU fallback when no supported GPU found: Arnold falls back to CPU rendering according to the value of the render_device_fallback option when there are no supported GPUs. (ARNOLD-16277)

• Improvements in geometry stats: Memory usage for top-level objects is now correctly calculated, and a new entry was added in memory stats. (ARNOLD-16350)

• One-to-one path mapping rules: The Arnold pathmap file now supports one-to-one mapping rules, which offers a simple method to replace exact path references. The rules are defined within the path_map section of the JSON file. (ARNOLD-16351)

{
    "path_map": {
        "linux": {
            "S:/textures/plastic_basecolor.exr": "plastic_basecolor.exr",
            "S:/textures/plywood_normal.exr": "/mnt/plywood_textures/01/normal.exr"
        }
    }
}

• Override output directory in kick: The kick command has a new argument -od that specifies an output directory path. This output directory is created if necessary, and added as a prefix to the output filenames specified by drivers in the scene. (ARNOLD-16513)

• Light visibility in procedurals: You can now disable all lights in a procedural by setting the procedural visibility to 0. Any non-zero visibility enables the lights. This is evaluated per-instance, so you can disable lights for some procedural instances and enable them for others. (ARNOLD-16206)

• OpenColorIO Aliases: You can now use OCIO aliases such as srgb_texture as input color spaces. The builtin OCIO config also supports the srgb_texture alias as well as other tweaks to be compatible with Maya 2026.2. (ARNOLD-16465, ARNOLD-16467)

• MaterialX 1.39.3: The MaterialX version is now 1.39.3, upgraded from 1.38.10. Consult the full MaterialX release notes for more details. (ARNOLD-16361)

USD Enhancements

• DomeLight texture, color, and temperature combinations: When a DomeLight primitive has a color along with a texture or temperature enabled, these features combined, instead of being mutually exclusive. usd#1405
• Volume shaders on points: Volume shaders are now supported when assigned to point primitives in Hydra usd#2310
• Overwrite stats mode: Overwrite mode for stats and deprecate the render setting stats:mode usd#2320
• Moving the timeline optimized in the procedural: When the current frame is modified, the procedural is no longer re-initialized automatically. This can provide faster updates in Maya or 3dsMax stage objects with animated usd files, as only the animated primitives are updated. usd#2352
• USD 25.05: Arnold USD now uses USD 25.05. See the USD release notes for more information.

API Changes

• Print a warning when a node is removed in batch mode: A warning is printed when a node is removed during scene update in batch render mode. In most cases, removing nodes in batch sessions can cause problems, and should be done in interactive render mode. (ARNOLD-16078)
• Deprecated AiStatsSetMode() and AiStatsGetMode(): Arnold now always overwrites the stats in the specified .json file. These API calls still work, but they now print a warning, and will eventually be removed. (ARNOLD-16413)
• Removed AtGPUCachePopulateCallback, AtGPUCachePopulateMode: The AtGPUCachePopulateCallback function type and the AtGPUCachePopulateMode enum became obsolete after Arnold was upgraded to OptiX 8 and are no longer used in the Arnold API. This does not require a recompilation of plugins. (ARNOLD-16229)

Incompatible Changes

• Automated output directory creation: Arnold now attempts to create missing directories for drivers instead of erroring out. (ARNOLD-3476)
• Visibility of lights in a procedural: Lights in procedurals are now affected by the visibility parameter. (ARNOLD-16206)
• Removed options.gpu_max_texture_resolution parameter: The GPU maximum texture resolution feature was removed in a previous version of Arnold, so the parameter no longer did anything. (ARNOLD-16272)
• Removed ability to append stats using -statsfile: The kick -statsfile flag now always overwrites stats in the specified .json file. (ARNOLD-16377)

Bug Fixes

• HTOA-2874 - The Arnold render delegate now stops rendering after switching to the viewport
• HTOA-2917 - Fixed the default value if the ar_cached_scene_units parm is missing
• HTOA-2602 - Fixed shop_materialpath on instanced volumes
• HTOA-2951 - Fixed incorrect bounds written into .ass files
• ARNOLD-16530 - Fixed errors with indexed normals in alembic files
• ARNOLD-16549 - Rare crash during GPU JIT compilation
• ARNOLD-16525 - Fix 7.4.2.1 performance regression when opening textures
• ARNOLD-16563 - Formatting errors for tables and stats in the Arnold Render Report
• usd#2307 - DomeLight connections are taken into account twice when written from an Arnold scene
• usd#2337 - Don't disable CER error reports through the hydra procedural
• usd#2346 - Node registry should consider arnold usd.hide metadata instead of DCC-specific ones
• usd#2333 - Fix crash in USD writer when the output string contains asterisks
• usd#2364 - Fix render delegate crash when using indexed UVs and shared arrays

System Requirements

• Houdini, Houdini FX, Houdini Indie and Houdini Education
  • 19.5.805
  • 20.0.896
  • 20.5.654
• Linux with at least glibc 2.28 and libstdc++ 9.3.1 (gcc 9.3.1) for Houdini 19.5, 20 and 20.5. This is equivalent to RHEL/CentOS 7.
• Linux with at least glibc 2.17 and libstdc++ 11.2.1 (gcc 11.2.1) for Houdini 20/20.5. This is equivalent to Rocky 8.
• macOS 11 or later
• Apple Mac models with M series chips are natively supported by HtoA
• x86-64 CPUs need to support the SSE4.1 instruction set. Apple Mac models with M series chip are supported natively mode.
• GPU rendering works on Windows and Linux only and requires an NVIDIA GPU with the Maxwell architecture or later.
  • On Linux, we recommend 570.153.02 or higher drivers.
  • On Windows, we recommend 573.42 or higher drivers.
• Optix™ denoiser requires an NVidia GPU with CUDA™ Compute Capability 5.0 and above.
• Intel OIDN GPU support is limited to:
  • MacOS
    • Apple native CPUs (M1 and newer)
  • Windows
    • Intel Xe dedicated and integrated GPUs
    • NVIDIA GPUs using Turing or newer architectures