KhronosGroup · ibouazizi · Jan 16, 2026
diff --git a/extensions/2.0/Khronos/KHR_gaussian_splatting_lgsc/README.md b/extensions/2.0/Khronos/KHR_gaussian_splatting_lgsc/README.md
@@ -0,0 +1,224 @@
+# KHR_gaussian_splatting_lgsc
+
+## Contributors
+- Imed Bouazizi, Qualcomm
+- Geert van der Auwera, Qualcomm
+
+## Status
+Draft
+
+## Dependencies
+Written against the glTF 2.0 specification.
+
+This extension depends on `KHR_gaussian_splatting`.
+
+## Overview
+L-GSC v1.0 is a codec for Gaussian Splat representations. It compresses the standard Gaussian splat attribute arrays into a single binary payload and later decompresses them back into attribute arrays suitable for rendering.
+
+This extension enables glTF to carry L-GSC compressed Gaussian splat data in a `bufferView`, instead of uncompressed attributes or meshopt compressed attributes.
+
+## L-GSC codec description
+This section is non normative.
+
+L-GSC (Lite Gaussian Splat Codec) is a scalar quantization and gzip based codec optimized for fast decoding. It encodes the standard INRIA Gaussian splat attributes (POSITION, SH DC, SH rest, OPACITY, SCALE, ROTATION) into a framed binary payload with the following structure:
+
+- Header segment (uncompressed): number of splats, per attribute bit depths, codec flags, and per dimension min/max values used for quantization.
+- Geometry segment: quantized positions, optionally Morton sorted to improve compression. Interleaving flags control whether values are stored by point or by dimension.
+- Attribute segment: quantized SH DC, SH rest, opacity, scale, and rotation data, encoded in a fixed attribute order.
+
+Before quantization, optional preprocess steps may be applied to improve compression. These include YUV conversion for SH rest coefficients, sigmoid mapping for opacity, rearranging SH rest coefficients to group channels, and a quaternion packing scheme that stores the index of the largest component and three remaining components. Each segment is length prefixed; geometry and attribute segments are typically gzip compressed.
+
+Decoding reverses the process by reading the header metadata, inverse quantizing each stream, and applying the inverse transforms. The codec treats splats as order agnostic, so the original point order may not be preserved if Morton sorting is enabled.
+
+## Adding L-GSC compressed data to primitives
+If a primitive contains the `KHR_gaussian_splatting` extension and that object includes `extensions.KHR_gaussian_splatting_lgsc`, then L-GSC decoding is required for that primitive.
+
+At this time, there is no requirement for a backup uncompressed buffer.
+
+The extension MUST be listed in `extensionsUsed` along with `KHR_gaussian_splatting`.
+
+```json
+"extensionsUsed": [
+  "KHR_gaussian_splatting",
+  "KHR_gaussian_splatting_lgsc"
+]
+```
+
+It MUST also be listed in `extensionsRequired`.
+
+```json
+"extensionsRequired": [
+  "KHR_gaussian_splatting",
+  "KHR_gaussian_splatting_lgsc"
+]
+```
+
+Note: `KHR_gaussian_splatting_lgsc` extends `KHR_gaussian_splatting`, so both are required to interpret the decoded attributes correctly.
+
+## Geometry type
+The `mode` of the primitive MUST be `POINTS`.
+
+## Schema example
+Example L-GSC extension shown below. This extension only affects primitives containing Gaussian splat data.
+
+```json
+{
+  "meshes": [
+    {
+      "primitives": [
+        {
+          "attributes": {
+            "POSITION": 0,
+            "KHR_gaussian_splatting:OPACITY": 1,
+            "KHR_gaussian_splatting:SH_DEGREE_0_COEF_0": 2,
+            "KHR_gaussian_splatting:SCALE": 3,
+            "KHR_gaussian_splatting:ROTATION": 4,
+            "KHR_gaussian_splatting:SH_DEGREE_1_COEF_0": 5,
+            "KHR_gaussian_splatting:SH_DEGREE_1_COEF_1": 6,
+            "KHR_gaussian_splatting:SH_DEGREE_1_COEF_2": 7
+          },
+          "material": 0,
+          "mode": 0,
+          "extensions": {
+            "KHR_gaussian_splatting": {
+              "kernel": "ellipse",
+              "colorSpace": "lin_rec709_scene",
+              "extensions": {
+                "KHR_gaussian_splatting_lgsc": {
+                  "bufferView": 0,
+                  "numPoints": 590392,
+                  "shDegree": 1,
+                  "compLevel": 2,
+                  "flags": 0,
+                  "attributes": {
+                    "POSITION": 0,
+                    "KHR_gaussian_splatting:OPACITY": 1,
+                    "KHR_gaussian_splatting:SH_DEGREE_0_COEF_0": 2,
+                    "KHR_gaussian_splatting:SCALE": 3,
+                    "KHR_gaussian_splatting:ROTATION": 4,
+                    "KHR_gaussian_splatting:SH_DEGREE_1_COEF_0": 5,
+                    "KHR_gaussian_splatting:SH_DEGREE_1_COEF_1": 6,
+                    "KHR_gaussian_splatting:SH_DEGREE_1_COEF_2": 7
+                  }
+                }
+              }
+            }
+          }
+        }
+      ]
+    }
+  ],
+  "buffers": [
+    {
+      "uri": "0.lgsc",
+      "byteLength": 8123456
+    }
+  ],
+  "bufferViews": [
+    {
+      "buffer": 0,
+      "byteLength": 8123456
+    }
+  ]
+}
+```
+
+## Extension properties
+
+### bufferView
+Type: `integer`. Required.
+
+The index of the `bufferView` that contains the L-GSC compressed bitstream.
+
+### attributes
+Type: `object`. Required.
+
+Maps `KHR_gaussian_splatting` attribute semantic names to accessor indices for the decompressed streams.
+
+At minimum it MUST contain the following keys.
+
+- `POSITION`
+- `KHR_gaussian_splatting:SH_DEGREE_0_COEF_0`
+- `KHR_gaussian_splatting:OPACITY`
+- `KHR_gaussian_splatting:ROTATION`
+- `KHR_gaussian_splatting:SCALE`
+
+`KHR_gaussian_splatting:SH_DEGREE_1_COEF_0` through `KHR_gaussian_splatting:SH_DEGREE_3_COEF_6` MAY be present to carry higher-order spherical harmonic coefficients, depending on `shDegree`.
+
+### numPoints
+Type: `integer`. Required.
+
+The number of Gaussian splats encoded in the bitstream.
+
+The accessor `count` for each listed decompressed attribute MUST match `numPoints`.
+
+### shDegree
+Type: `integer`. Required. Range 0 to 3.
+
+The spherical harmonic degree represented by the decompressed data. The number of higher order coefficient vectors is
+
+`F = (shDegree + 1) * (shDegree + 1) - 1`
+
+These coefficients are mapped to `KHR_gaussian_splatting:SH_DEGREE_1_COEF_0` through `KHR_gaussian_splatting:SH_DEGREE_3_COEF_6`.
+
+- `shDegree = 0` means only `KHR_gaussian_splatting:SH_DEGREE_0_COEF_0` is present.
+- `shDegree = 1` means `KHR_gaussian_splatting:SH_DEGREE_1_COEF_0` to `KHR_gaussian_splatting:SH_DEGREE_1_COEF_2` may be present.
+- `shDegree = 2` means `KHR_gaussian_splatting:SH_DEGREE_1_COEF_0` to `KHR_gaussian_splatting:SH_DEGREE_2_COEF_4` may be present.
+- `shDegree = 3` means `KHR_gaussian_splatting:SH_DEGREE_1_COEF_0` to `KHR_gaussian_splatting:SH_DEGREE_3_COEF_6` may be present.
+
+### compLevel
+Type: `integer`. Optional. Range 0 to 2.
+
+The compression level used during encoding. This is informative metadata.
+
+### flags
+Type: `integer`. Optional. Default 0.
+
+Reserved bit flags for future use.
+
+## Attribute mapping
+This extension uses the same attribute names as `KHR_gaussian_splatting`.
+
+| Splat data | glTF attribute | Accessor type | Component type | Required |
+| --- | --- | --- | --- | --- |
+| Position | `POSITION` | `VEC3` | `FLOAT` | yes |
+| Diffuse color (SH0 DC) | `KHR_gaussian_splatting:SH_DEGREE_0_COEF_0` | `VEC3` | `FLOAT` | yes |
+| Alpha | `KHR_gaussian_splatting:OPACITY` | `SCALAR` | `FLOAT` | yes |
+| Rotation | `KHR_gaussian_splatting:ROTATION` | `VEC4` | `FLOAT` | yes |
+| Scale | `KHR_gaussian_splatting:SCALE` | `VEC3` | `FLOAT` | yes |
+| SH coefficients | `KHR_gaussian_splatting:SH_DEGREE_1_COEF_0` to `KHR_gaussian_splatting:SH_DEGREE_3_COEF_6` | `VEC3` | `FLOAT` | no |
+
+## Accessors
+Accessors MUST be defined for each attribute listed in `KHR_gaussian_splatting.extensions.KHR_gaussian_splatting_lgsc.attributes`.
+
+Each accessor MUST define `componentType`, `count`, and `type`.
+
+The accessor `count` MUST match `numPoints`.
+
+The accessor `type` and `componentType` describe the decompressed data after decoding.
+
+## Conformance
+A loader MUST follow this process.
+
+1. If the loader does not support `KHR_gaussian_splatting_lgsc`, it MUST fail to load the asset when the extension is required.
+2. If the loader does support `KHR_gaussian_splatting_lgsc` then it MUST do the following.
+   1. Read the L-GSC payload from `KHR_gaussian_splatting.extensions.KHR_gaussian_splatting_lgsc.bufferView`.
+   2. Decode the payload to obtain attribute arrays for the attributes referenced by `KHR_gaussian_splatting.extensions.KHR_gaussian_splatting_lgsc.attributes`.
+   3. When processing those referenced attributes, the loader MUST ignore any accessor `bufferView` and `byteOffset` and instead use the decoded streams.
+   4. Any primitive attributes not listed in `KHR_gaussian_splatting.extensions.KHR_gaussian_splatting_lgsc.attributes` MUST be processed normally.
+
+## Implementation
+This section is non normative.
+
+A common implementation path is to decode the payload once, then either populate GPU buffers matching the accessor layout, or render directly from the decoded arrays.
+
+An implementation may choose to also populate `COLOR_0` for point-cloud fallback. This attribute is outside of the `KHR_gaussian_splatting` semantics and is ignored by this extension.
+
+## Schema
+- [`schema/KHR_gaussian_splatting_lgsc.schema.json`](schema/KHR_gaussian_splatting_lgsc.schema.json)
+
+## Known implementations
+- Reference codec library and sample API usage are available in the Qualcomm lite-3Dgsplat-codec repository.
+
+## Resources
+- https://github.com/qualcomm/lite-3Dgsplat-codec
diff --git a/...ns/2.0/Khronos/KHR_gaussian_splatting_lgsc/schema/KHR_gaussian_splatting_lgsc.schema.json b/...ns/2.0/Khronos/KHR_gaussian_splatting_lgsc/schema/KHR_gaussian_splatting_lgsc.schema.json
@@ -0,0 +1,87 @@
+{
+  "$schema": "http://json-schema.org/draft-07/schema",
+  "title": "KHR_gaussian_splatting_lgsc primitive extension",
+  "type": "object",
+  "allOf": [
+    {
+      "$ref": "glTFProperty.schema.json"
+    }
+  ],
+  "properties": {
+    "bufferView": {
+      "type": "integer",
+      "minimum": 0,
+      "description": "The bufferView that contains the L-GSC compressed bitstream."
+    },
+    "numPoints": {
+      "type": "integer",
+      "minimum": 0,
+      "description": "Number of Gaussian splats encoded in the payload."
+    },
+    "shDegree": {
+      "type": "integer",
+      "minimum": 0,
+      "maximum": 3,
+      "description": "Spherical harmonic degree represented by the decompressed data (0 to 3)."
+    },
+    "compLevel": {
+      "type": "integer",
+      "minimum": 0,
+      "maximum": 2,
+      "description": "Informative compression level used during encoding (0 to 2)."
+    },
+    "flags": {
+      "type": "integer",
+      "minimum": 0,
+      "default": 0,
+      "description": "Reserved bit flags for future use."
+    },
+    "attributes": {
+      "type": "object",
+      "description": "Maps KHR_gaussian_splatting attribute semantics to accessor indices for the decompressed streams.",
+      "properties": {
+        "POSITION": {
+          "type": "integer",
+          "minimum": 0
+        },
+        "KHR_gaussian_splatting:SH_DEGREE_0_COEF_0": {
+          "type": "integer",
+          "minimum": 0
+        },
+        "KHR_gaussian_splatting:OPACITY": {
+          "type": "integer",
+          "minimum": 0
+        },
+        "KHR_gaussian_splatting:ROTATION": {
+          "type": "integer",
+          "minimum": 0
+        },
+        "KHR_gaussian_splatting:SCALE": {
+          "type": "integer",
+          "minimum": 0
+        }
+      },
+      "patternProperties": {
+        "^KHR_gaussian_splatting:SH_DEGREE_[1-3]_COEF_([0-9]|1[0-5])$": {
+          "type": "integer",
+          "minimum": 0
+        }
+      },
+      "required": [
+        "POSITION",
+        "KHR_gaussian_splatting:SH_DEGREE_0_COEF_0",
+        "KHR_gaussian_splatting:OPACITY",
+        "KHR_gaussian_splatting:ROTATION",
+        "KHR_gaussian_splatting:SCALE"
+      ],
+      "additionalProperties": false
+    }
+  },
+  "required": [
+    "bufferView",
+    "numPoints",
+    "shDegree",
+    "attributes"
+  ],
+  "additionalProperties": false
+}
diff --git a/extensions/README.md b/extensions/README.md
@@ -44,6 +44,7 @@ This section tracks the status of extensions and projects that are in developmen
 | KHR_accessor_float64 | Review Draft | [PR #2397](https://github.com/KhronosGroup/glTF/pull/2397) |
 | KHR_audio_graph | Proposal | [PR #2421](https://github.com/KhronosGroup/glTF/pull/2421) |
 | KHR_collision_shapes | Review Draft | [PR #2370](https://github.com/KhronosGroup/glTF/pull/2370) |
+| KHR_gaussian_splatting_lgsc | Initial Draft | [Specification](2.0/Khronos/KHR_gaussian_splatting_lgsc/README.md) |
 | KHR_interactivity | Review Draft | [PR #2293](https://github.com/KhronosGroup/glTF/pull/2293) |
 | KHR_materials_diffuse_transmission | Release Candidate | [Specification](2.0/Khronos/KHR_materials_diffuse_transmission/README.md) |
 | KHR_materials_subsurface | Initial Draft | [PR #1928](https://github.com/KhronosGroup/glTF/pull/1928) |