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A model of a Western Pacific locomotive derailed on a desert landscape. The train is tilted, with visible sparks near the wheels, and blue skies with scattered clouds in the background. Tracks extend away into the distance.

Houdini 21 : Otto, Otis, Copernicus and 300+ New Features. No, Really

05.08.2025
Houdini 21 sneak peek: SideFX previews 300+ features: Otis solver, Otto rig, Copernicus, Vulkan viewport, full rigging and CFX overhaul.

SideFX has released a feature crawl for Houdini 21, and if you blink, you’ll miss roughly a dozen new features. The SIGGRAPH 2025 sneak peek video runs down over 300 updates, upgrades and experimental toys, making Houdini 21 the biggest “dot one” in SideFX’s history. From rigging to viewport, the list reads like a wishlist for every CG department plus some surprises.

Houdini 21 Sneak Peak

Houdini 21: KineFX, Animation, and Otto, so Drag, Drop, and Deform

Animators get new auto-rig modules for limbs, feet, hands, necks, scapulae, and ulnae, plus a version 3.0 spine rig with squash and stretch, and an updated Electra rig with twist joints, reverse foot, bendable IK/FK, and a proper clavicle.

A 3D model of a muscular human figure in a running pose, displayed in a digital graphics software interface. The model features visible muscle and tissue rigging, with a dark gradient background.

Houdini 21 brings procedural graph fusion for rapid rig generation, a drag-and-drop viewport rig builder, and a rigging environment that’s now APEX-driven and designed for actual animators, not just TDs.

3D model of a human skeleton displayed in a software interface with sliders and options for adjusting muscle and bone geometry. A label at the bottom reads 'Muscle Transfer: transfer muscle and bones geometry between characters.'

There’s also Otto: a fully rigged, production-ready human with muscle and tissue simulation out-of-the-box. Ragdoll and constraint upgrades include soft/hard tethers, LookAt and Static types, offset controls, mirrored keyframes, and improved full-body IK posing. Motion Mixer (beta) is in, with tracks, non-linear animation mixing, and full APEX support. ML-driven skin deformation and neural point surfacing round out the “futuristic but real” vibe.

3D model of a human upper body showing muscle and tissue structure. Displayed on the left, the model is textured with a mesh appearance. On the right, a software interface with settings for adjustments.
Close-up of a 3D muscle model showing red muscle tissue with a geometric wireframe. A user interface panel on the right shows adjustable settings for the model.

Otis and CFX: Muscles with (Machine) Learning

The Otis solver is SideFX’s new GPU-accelerated organic tissue simulation engine, delivering FEM-grade accuracy, real-time APEX animation, muscle/fat collision, and muscle constraint nodes. It’s set up to transfer muscle rigs and bone geometry between characters, and includes ML-deform tools for both default and user-trained anatomical datasets.

Houdini’s CFX arsenal adds real-time painting and sculpting upgrades: new elastic, plow, and planar brushes, adaptive quad remeshing, interactive edge-flow, and in-node sculpt mask management. Mesh overlap, subdivision, and group support have all improved. Muscle system upgrades include tension control, automatic multiple tension lines, deintersecting SOPs, and procedural activation.

A glass bowl with several round cookies inside, placed on a dark surface scattered with coffee beans. In the background, a glass tool is partially visible.
A glass bowl filled with crushed chocolate cookies. A metal spoon is visible, partially submerged in the cookie crumbs.
A close-up of a clear glass mug with layers of chocolate and milk mixing together. Dark coffee beans and sugar are scattered on a dark surface around the mug.

Simulation and Modeling: Pyro, Particles, and Point Clouds

MPM simulation (think granular materials) adds debris emission, surface tension, and deterministic particle-grid flows. Pyro gets real-time, ML-powered upres and a new sparse solver for smoke and fire, callable from SOPs and COPs.

A split image showing a yellow flower on the left labeled 'REF' and a similarly styled yellow flower on the right labeled 'NPS (L)'. The two sides highlight differences in detail and texture.

Modelers get support for complex topology operations, UV/UDIM management, string-based selection, updated paint workflows, and procedural terrain via the Dryad biome toolkit (now with full integration to Solaris and Unreal). Neural Point Surfacing provides AI-driven realism for fluid and mesh point clouds.

A 3D rendered landscape model showing elevated terrain with peaks and valleys. On the right, a panel displays various editing nodes related to heightfield manipulation, labeled with terms like 'heightfield_noise' and 'heightfield_erosion'. The bottom displays a software title 'HeightField Erode 3.0'.
3D terrain model shown on the left with orange and purple gradients. On the right, a software interface displays nodes and controls for environmental building, with a highlighted node and various connected inputs.

Rendering, Vulkan, Copernicus: For the Eyes and the GPU

Karma XPU and CPU renderers see speed boosts, subdivision support, improved path tracing, Intel OIDN 2.2.1 denoising, deep output support, and robust motion blur. The Vulkan viewport is officially “production-ready,” with full OpenGL parity, ray-traced AO, physical sky, multithreaded updates, no forced far clipping, and automated VRAM management. Copernicus (the in-house image-processing framework) brings real-time USD rendering, noise types, handle binding, and compositor enhancements.

An underwater scene with blue water and scattered rocks. Light creates reflections on the water surface, highlighting the colors. Text at the bottom mentions geometry lights for rendering.

Pipeline, Engine, and Labs: More Glue, Fewer Bottlenecks

PDG gets ML training nodes for style transfer and denoising, ROP/GLTF export, Preflight tools, and faster pipeline execution. Houdini Engine now supports Unreal 5.5/5.6, Unity 6.0/6.1, and Maya/3ds Max 2026, with Python nanobind GPU, speedier shared memory, and snappier startup. The UI is cleaned up with streamlined multiparm controls, hotkey binding, recipe subnets, live simulation toggling, and autocomplete.

Labs tools gain the new Dryad biome system, ZibraVDB integration, a computer-vision toolkit for synthetic data generation, improved Unreal VAT workflows, and even Perforce integration for those who enjoy version control with their chaos.

Eight textured spheres arranged in two rows. The top row features a dark lava texture, a smooth beige texture, a light gray sphere, and an orange sphere with drips. The bottom row includes a matte gray sphere, a dark sphere with green accents, and a rough, brown sphere.

The Full Houdini 21 Feature List (per the sneak peek video and forum transcript)

KineFX and APEX-driven animation

Production-ready for riggers and animators, additional auto-rig components (limb, hand, foot, neck, scapula, ulna), spine rig v3.0 with squash & stretch, enhanced reverse foot, viewport drag‑and‑drop rig builder, rapid facial rig creation, procedural auto‑rig via graph fusion, updated Electra rig (twist joints, reverse foot, clavicle, bendable IK/FK), Otto human rig v1.0, APEX graph and scripting enhancements, fast in-place APEX cooking of SOP verbs, nodes for converting KineFX to packed folders.

A 3D model of a character with blue hair and large yellow eyes. The character is displayed in a gray background with control points around the face indicating facial rigging. Text at the bottom reads 'Custom facial rig'.

Ragdoll and constraints

Streamlined configuration, animatable ragdoll parameters (stiffness, damping, length), multi-constraint system, soft/hard tethers, Parent/Static/LookAt types, offset control, mirrored keyframes, full-body IK posing, animation layer inheritance in APEX, hotkeys for selection, unified baking workflow, IK/FK switching.

Animation tools and Graph Editor

Ripple tool, enhanced control sets, pick-walking with heuristics, hide controls on scrub, animatable control feedback, direct skin manipulation, upcoming GPU skin/blend shape deformation, customizable 3D handles, new FFmpeg audio, Scene Add Prop node supports deformation, animation transfer via APEX, up to 6× faster panning, new Animation Catalog (pose library), Motion Mixer (beta), APEX motion mixing, ML-driven skin deformation, neural point surfacing, AMD® NeuronNet backend, hand motion tracking, joint-based retargeting, glTF importer for skinned assets, UX polish throughout.

3D anatomical model of a horse showing muscles and skeleton structure. The model is semi-transparent with red muscles and white bones. The background is dark, with a software interface visible at the bottom.
3D model of a horse showing muscles and skeletal structure, with emphasis on the hindquarters. The image also features labels for the GPU-accelerated organic tissue solver.
A 3D model of a dog in two views: the left side shows a plain white dog model, while the right side displays the dog with visible muscles and skeletal structure in red. The background is dark gray.

CFX: Organic Tissue Simulation (Otis)

GPU-accelerated organic solver, FEM-level quality, robust muscle/fat collision, muscle/tissue config nodes, new mesh generation, Otto’s anatomy, ML Deform with user recipes, real-time APEX animation, Armature Deform, Organic Deformer, muscle deintersect, flex SOP with activation, tension line automation, UI for muscle properties, procedural tension activation, new sculpt brushes, adaptive remeshing, mask tools, contour extraction, unsubdivide, faster Paint SOP, UDIM/alpha paint, bidirectional Ray SOP, curves can branch/cut/join, edge-flow controls, string attribute groups, poly extrude upgrades, overlap resolution.

A digital rendering of billowing smoke displayed on the left, with software interface and settings for the smoke effect on the right. Various nodes and parameters are visible in the interface.

Rendering and XPU

Optimized XPU shader compilation, volumetric light in XPU, uniform volume rendering, opacity/background holdout, shadow linking, blending up to 16 MtIX Standard Surfaces, string primvars, MIS compensation, hardware selection, Gaussian splats support.

A 3D visual displaying two different smoke simulations: one is a white smoke plume and the other is a swirling flame effect. Both are within separate transparent boxes against a dark background. The bottom of the image includes text about a volumetric solver for simulations.

Generators and integration

2D shape generator, hex grid generator, attribute visualization, updated AliceVision/RizomUV/Exoside integration, point-cloud exporter, Unreal plugin with PCG, spline round-trip Houdini/Unreal, Unreal plugin VAT import, computer-vision tools, Perforce integration.

Vulkan viewport

Production-ready, OpenGL parity, raytraced AO, area lights, denoising, dome/sky/headlight, instanced USD lights, OpenPBR shaders, multithreaded, free camera, preserves clipping planes, texture cache resizing.

All these features come from the SideFX sneak peek – some items were not legible in the video, so verify with SideFX documentation after the release before betting the farm.

Bela Beier Author