18 June 2026

Arnold for Houdini (HtoA) 6.5.2.0 is a feature release using Arnold 7.5.2.0. Arnold 7.5.2.0 includes optimized nested instancers in USD and matte support in Hydra 2 Render Passes. This release adds live Copernicus textures in Solaris, Gaussian splat support, and more.

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

Flow Render Tech Preview

HtoA 6.5.2.0 beta includes a Tech Preview of Flow Render, an Arnold cloud-rendering solution. We are providing 2400 minutes (per user, per month) of rendering time to Arnold users for testing and evaluating the service. Please report any feedback or issues in the Arnold feedback forums.

See the Flow Render Tech Preview documentation for more information.

Enhancements

• Live Copernicus textures in Solaris: Solaris materials can use op: and opdef: texture paths from Copernicus networks interactively. (HTOA-2655)

• Gaussian splats: HtoA now supports rendering 3D Gaussian Splatting scenes through the Arnold Points node with Mode set to Gaussian. You can load .ply files from standard 3DGS tools or drive splats from point attributes, and shade them with the Gaussian Splat Shader. In Solaris, use the Bake GSplat workflow to bake splat data and bring the points into your USD stage for rendering with Arnold. (HTOA-3265)

• VOP bypass and debug in IPR: Arnold shader VOP nodes now respect the Houdini Bypass and Debug flags during IPR. Use Bypass to disable nodes, or Debug to inspect intermediate results—including pattern soloing in Solaris—without rewiring the shader network. (HTOA-926, HTOA-141, HTOA-2214)

• Improved quality of noice denoiser: Previously, the noice denoiser could produce overly-blurred denoised images even with sufficient samples. This noice improvement also fixes occasional black pixel artifacts introduced by the denoiser. The variance parameter on the noice imager has been renamed to filter_strength; the old name is still accepted as a synonym. The standalone tool's --variance/-v flags are kept as aliases for --filter_strength/-k. In the example below, note the improved denoising of the sweater, the fur, and the whiskers. (ARNOLD-14879)

• Noice variance: HtoA now passes variance-of-the-sample-mean to the Noice imager, matching the Arnold adaptive sampling metric so denoising scales correctly as more samples are added. (HTOA-3256)

• Shader to RGBA: The new shader_to_rgba node evaluates lighting for a surface shader (such as openpbr_surface) and outputs the result as RGBA that you can use in a shading tree. For example, you could feed those RGBA values into a ramp for non-photorealistic rendering. Both direct and indirect illumination are available as separate outputs, and a light group filter allows for per-light stylization. shader_to_rgba works on both CPU and GPU (out_indirect is not yet available on GPU). (ARNOLD-17679)

_{OpenPBR Surface > Shader to RGBA > Tone Zone shader}

• Faster GPU scene updates: Several optimizations make GPU scene updates noticeably faster, especially for interactive edits to meshes, with update times reduced by up to 43%. (ARNOLD-17720, ARNOLD-17721)

• Tone zones: The new tone_zones node splits lighting into up to eight discrete brightness bands for cel-shading and non-photorealistic-rendering workflows. Zone widths are defined as simple ratios and stay stable across exposure changes. Each zone outputs a tint color and a mask that you can use for compositing. You can soften boundaries between zones independently, and chain nodes to further subdivide a zone. (ARNOLD-17680)

• Improved point cloud queries: You can now query point clouds for up to 1024 nearest points, and the pointcloud_search and pointcloud_get built-in functions now work on GPUs. (ARNOLD-17285, ARNOLD-17364)
• Per-subimage compression for multipart EXRs: The EXR driver now supports per-subimage compression for multipart EXR files. (ARNOLD-15669)
• Faster loading of PLY file meshes: Loading meshes from PLY files is now generally about 1.2x to 1.4x faster. (ARNOLD-17584)
• Overlay imager default font: Instead of erroring out, the Overlay imager now tries to render with a default system font, like Arial or Liberation Sans, if the user-specified font is not available. (ARNOLD-17759)
• Options node in render reports: Render reports now include the options node parameters (Arnold's global render settings), so you can see exactly which settings were active when reviewing performance data. (ARNOLD-17099)

• Override node and string arrays in kick: You can now override node and string array type parameters, such as options.drivers or options.outputs, using the -set command in kick. (ARNOLD-17816, ARNOLD-17821)

• Motion blur on Arnold ROP: The Arnold ROP and render settings expose ignore_motion_transform and ignore_motion_deform that can disable the two types of motion blur independently. On the Arnold ROP only, transform_keys and deform_keys may be set to 0, which implicitly enables the matching ignore option. (ARNOLD-17112, HTOA-3262)

• Upgraded OSL: OSL has been upgraded to version 1.14.2.0. (ARNOLD-17651)
• Upgraded MaterialX: MaterialX has been upgraded to version 1.39.5. (ARNOLD-17572)
• Upgraded OpenColorIO: OpenColorIO has been upgraded to version 2.5.2. (ARNOLD-17725)

Flow Render Enhancements

• Multipart uploads: File uploads are no longer limited to 5 GB, as large files are now uploaded in multiple parts. (ARNOLD-17554)
• Verify scene outputs and camera: Render outputs and camera are now verified when the scene is submitted and will trigger a submission failure when missing. (ARNOLD-17661)

USD Enhancements

• Interactive texture updates in Solaris: Textures are now flushed when cop_texture_changed is triggered, enabling correct interactive texture updates in Solaris. usd#2626

• Optimized nested instancers: The new lightweight instancing scheme has now been extended to nested procedurals. usd#2583

• Matte in Render Passes: In Hydra 2, Render passes now support the matte attribute with Arnold usd#2549

• ArnoldNodeGraph in referenced USD files: ArnoldNodeGraph primitives are now correctly resolved when the USD file containing them is referenced into a larger stage. usd#2645

• Gaussian Splat USD schema: Arnold now has preliminary support for reading the USD 26.03 ParticleField3DGaussianSplat schema, allowing Gaussian Splat data authored in USD to be rendered. usd#2608

• Full UsdLux support: Arnold now implements the current UsdLux lighting standard for USD lights, enabled by setting the options node usdlux_version parameter to 25.05. Cone shaping (cone angle, softness, focus, and focus tint) and IES photometric profiles now work on all light types (cylinder, disk, quad, and mesh lights, not just spot and sphere lights), together with IES orientation, angle-scale, and brightness-normalization controls. See USD Lux for the full feature list and more examples. usd#2439

  Cone angle: You can restrict area light emission to a cone around its primary axis:

IES profiles: You can now use IES profiles with non-sphere lights.

• Hole Indices support: Hole indices are now supported in UsdGeomMesh for non-subdivided meshes. usd#2632

API Changes

• Texture plugin API: Arnold's texture system can now be extended with live, procedural image data. Plugin authors register a custom URI prefix with AiTexturePluginRegisterURI() and supply pixels through AtTexturePluginCallbacks when an image shader points at that URI. Arnold treats the result like any other texture, including filtering and mipmapping, but the pixels can be generated on demand instead of being read from disk. That makes it practical to wire in host-native procedural sources without baking intermediate files. See ai_texture.h for the callback interface and an example implementation. (ARNOLD-17820)

• Profile write and reset: Profiling data can now be explicitly written to the profile file and cleared (reset). Previously, profile data was written and reset only when Arnold was unloaded or when the process exited. Two new functions have been added for this purpose: void AiProfileWrite() and void AiProfileReset(). Note that both functions immediately resume collecting profiling data after execution. (ARNOLD-11923)

• Per-subimage compression for multipart EXRs: To support per-subimage compression for multipart EXR files, the EXR driver compression parameter is now a string array. This allows you to use a different compression type for each subimage. (ARNOLD-15669)

Bug Fixes

• HTOA-3216 - Editing a MaterialX shader in IPR no longer requires restarting the render for changes to appear
• HTOA-3276 - OpenPBR Surface emission is preserved when switching between shader definition versions
• HTOA-3277 - MaterialX stack trace in dropdown
• HTOA-3278 - Reduced delay when editing large Arnold shader networks in Solaris Material Library
• ARNOLD-15737 - Fix Ctrl+C (SIGINT) being ignored when Arnold is run in background or automated runs
• ARNOLD-17113 - Rare AiMicrofacetThinWallRefractionBSDF sampling artifact
• ARNOLD-17581 - Memory for adaptive sampling buffers was allocated even with adaptive disabled
• ARNOLD-17599 - Enabling OIDN/OptiX denoiser causes Closest Filter width to match beauty
• ARNOLD-17667 - Rare crash in GPU volumes with velocity grids
• ARNOLD-17769 - Fix random crash/hang at process exit caused by AiMsg calls when missing AiEnd
• ARNOLD-17825 - No anti-aliasing on contour_filter output if there is a denoiser imager (even if the imager is disabled)
• ARNOLD-17885 - Render reports with built in stats do not work

System Requirements

• Houdini, Houdini FX, Houdini Indie, and Houdini Education

  • 20.0.896
  • 20.5.684
  • 21.0.729

• Flow Render is available for the default Houdini Qt versions ( Qt6 for Houdini 21, and Qt5 for Houdini 20.5 and Houdini 20.0)

• Linux with at least glibc 2.28 and libstdc++ 11.2.1 (gcc 11.2.1). 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.

• GPU rendering and OptiX denoising work on Windows and Linux only, and require an NVIDIA GPU with the Maxwell architecture or later.

  • On Linux, we recommend 590.48 or higher drivers.
  • On Windows, we recommend 591.28 or higher drivers.

• Intel OIDN runs on all CPUs. GPU support is limited to:

  • macOS
    • Apple silicon GPUs (M1 and newer)
  • Linux
    • NVIDIA GPUs with Turing, Ampere, Ada Lovelace, Hopper, and Blackwell architectures
  • Windows
    • Intel Xe and Intel Arc dedicated and integrated GPUs
    • NVIDIA GPUs with Turing, Ampere, Ada Lovelace, Hopper, and Blackwell architectures
    • AMD GPUs with RDNA 2, RDNA 3, RDNA 3.5, and RDNA 4 architectures