Khronos glTF extension for storing 3D Gaussian splats as point cloud primitives, plus its SPZ compression child extension.

KHR_gaussian_splatting

Source: https://github.com/KhronosGroup/glTF/blob/main/extensions/2.0/Khronos/KHR_gaussian_splatting/README.md Status: Release Candidate (2026)

Overview

Defines basic support for storing 3D Gaussian splats in glTF assets as point cloud primitives.

Splats are defined by: position, rotation, scale, opacity, and spherical harmonics.

Extension Object Properties

Property	Type	Description	Required
kernel	string	Gaussian kernel type	Yes
colorSpace	string	Color space of reconstructed values	Yes
projection	string	Projection method	No (default: "perspective")
sortingMethod	string	Sorting method for rendering	No (default: "cameraDistance")

Ellipse Kernel Attributes

Splat Data	Attribute Semantic	Type	Required
Position	POSITION	VEC3 float	Yes
Rotation	KHR_gaussian_splatting:ROTATION	VEC4 float/byte/short normalized	Yes
Scale	KHR_gaussian_splatting:SCALE	VEC3 float/ubyte/ushort	Yes
Opacity	KHR_gaussian_splatting:OPACITY	SCALAR float/ubyte/ushort normalized	Yes
SH degree 0	KHR_gaussian_splatting:SH_DEGREE_0_COEF_0	VEC3 float	Yes
SH degree 1	KHR_gaussian_splatting:SH_DEGREE_1_COEF_[0-2]	VEC3 float	No
SH degree 2	KHR_gaussian_splatting:SH_DEGREE_2_COEF_[0-4]	VEC3 float	No
SH degree 3	KHR_gaussian_splatting:SH_DEGREE_3_COEF_[0-6]	VEC3 float	No

Covariance Matrix

Σ = M·C·Cᵀ·Mᵀ

Where M = upper-left 3×3 of node transform, C = scale×rotation matrix.

Spherical Harmonics Color

Color = SH_0,0 × 0.2820947917738781 + 0.5

(plus higher degree terms for view-dependent color)

JSON Example

{
  "meshes": [{ "primitives": [{
    "attributes": {
      "POSITION": 0,
      "KHR_gaussian_splatting:SCALE": 2,
      "KHR_gaussian_splatting:ROTATION": 3,
      "KHR_gaussian_splatting:OPACITY": 4,
      "KHR_gaussian_splatting:SH_DEGREE_0_COEF_0": 5
    },
    "mode": 0,
    "extensions": {
      "KHR_gaussian_splatting": {
        "kernel": "ellipse",
        "colorSpace": "srgb_rec709_display"
      }
    }
  }]}]
}

Full Specification

See full spec at: https://github.com/KhronosGroup/glTF/blob/main/extensions/2.0/Khronos/KHR_gaussian_splatting/README.md

Compression extension: KHR_gaussian_splatting_compression_spz_2

Source: https://github.com/KhronosGroup/glTF/pull/2531 Status: Draft (2026)

Extension for compressing 3D Gaussian splats using the SPZ v2 format (Niantic Spatial). Depends on KHR_gaussian_splatting above.

Usage

"extensions": {
  "KHR_gaussian_splatting": {
    "extensions": {
      "KHR_gaussian_splatting_compression_spz_2": {
        "bufferView": 0
      }
    }
  }
}

"extensionsUsed": ["KHR_gaussian_splatting", "KHR_gaussian_splatting_compression_spz_2"]

SPZ → glTF Attribute Mapping

SPZ field	glTF Attribute	Conversion
positions	POSITION	—
colors	COLOR_0 RGB	0.5 + 0.282095 × x
alphas	COLOR_0 A	sigmoid(x) = 1/(1+e^-x)
scales	KHR_gaussian_splatting:SCALE	exp(x)
rotations	KHR_gaussian_splatting:ROTATION	—
sh[0..2]	SH_DEGREE_1_COEF_0	—
sh[3..5]	SH_DEGREE_1_COEF_1	—
sh[6..8]	SH_DEGREE_1_COEF_2	—
sh[9..44]	SH_DEGREE_2..3_COEF_*	—

Coordinate system: Left-Up-Front (LUF) in SPZ PackOptions/UnpackOptions for glTF compatibility.

Resources

SPZ format: https://github.com/nianticlabs/spz
PR: https://github.com/KhronosGroup/glTF/pull/2531

KHR gaussian splatting