diff --git a/packages/cli/src/cli.ts b/packages/cli/src/cli.ts
index e6870340a..1ac6a3d26 100755
--- a/packages/cli/src/cli.ts
+++ b/packages/cli/src/cli.ts
@@ -1076,6 +1076,29 @@ compression methods are typically more forgiving than GPU texture compression,
 and require less tuning to achieve good visual and filesize results.
 `.trim();
 
+// AVIF
+program
+	.command('avif', 'AVIF texture compression')
+	.help(TEXTURE_COMPRESS_SUMMARY.replace(/{VARIANT}/g, 'AVIF'))
+	.argument('<input>', INPUT_DESC)
+	.argument('<output>', OUTPUT_DESC)
+	.option(
+		'--formats <formats>',
+		'Texture formats to include (glob)',
+		{validator: ['image/png', 'image/jpeg', '*'], default: '*'}
+	)
+	.option(
+		'--slots <slots>',
+		'Texture slots to include (glob)',
+		{validator: program.STRING, default: '*'}
+	)
+	.action(({args, options, logger}) => {
+		const formats = micromatch.makeRe(String(options.formats), MICROMATCH_OPTIONS);
+		const slots = micromatch.makeRe(String(options.slots), MICROMATCH_OPTIONS);
+		return Session.create(io, logger, args.input, args.output)
+			.transform(textureCompress({targetFormat: 'avif', encoder: sharp, formats, slots}));
+	});
+
 // WEBP
 program
 	.command('webp', 'WebP texture compression')
diff --git a/packages/extensions/src/constants.ts b/packages/extensions/src/constants.ts
index 9ebd2debc..33710bee2 100644
--- a/packages/extensions/src/constants.ts
+++ b/packages/extensions/src/constants.ts
@@ -1,6 +1,7 @@
 export const EXT_MESH_GPU_INSTANCING = 'EXT_mesh_gpu_instancing';
 export const EXT_MESHOPT_COMPRESSION = 'EXT_meshopt_compression';
 export const EXT_TEXTURE_WEBP = 'EXT_texture_webp';
+export const EXT_TEXTURE_AVIF = 'EXT_texture_avif';
 export const KHR_DRACO_MESH_COMPRESSION = 'KHR_draco_mesh_compression';
 export const KHR_LIGHTS_PUNCTUAL = 'KHR_lights_punctual';
 export const KHR_MATERIALS_CLEARCOAT = 'KHR_materials_clearcoat';
diff --git a/packages/extensions/src/ext-texture-avif/index.ts b/packages/extensions/src/ext-texture-avif/index.ts
new file mode 100644
index 000000000..88ad7bee9
--- /dev/null
+++ b/packages/extensions/src/ext-texture-avif/index.ts
@@ -0,0 +1 @@
+export * from './texture-avif';
diff --git a/packages/extensions/src/ext-texture-avif/texture-avif.ts b/packages/extensions/src/ext-texture-avif/texture-avif.ts
new file mode 100644
index 000000000..cceaf8fdc
--- /dev/null
+++ b/packages/extensions/src/ext-texture-avif/texture-avif.ts
@@ -0,0 +1,171 @@
+import {
+	Extension,
+	ImageUtils,
+	ImageUtilsFormat,
+	PropertyType,
+	ReaderContext,
+	WriterContext,
+	vec2,
+	BufferUtils,
+} from '@gltf-transform/core';
+import { EXT_TEXTURE_AVIF } from '../constants';
+
+const NAME = EXT_TEXTURE_AVIF;
+
+class AVIFImageUtils implements ImageUtilsFormat {
+	match(array: Uint8Array): boolean {
+		return array.length >= 12 && BufferUtils.decodeText(array.slice(4, 12)) === 'ftypavif';
+	}
+	/**
+	 * Probes size of AVIF or HEIC image. Assumes a single static image, without
+	 * orientation or other metadata that would affect dimensions.
+	 */
+	getSize(array: Uint8Array): vec2 | null {
+		if (!this.match(array)) return null;
+
+		// References:
+		// - https://stackoverflow.com/questions/66222773/how-to-get-image-dimensions-from-an-avif-file
+		// - https://github.com/nodeca/probe-image-size/blob/master/lib/parse_sync/avif.js
+
+		const view = new DataView(array.buffer, array.byteOffset, array.byteLength);
+
+		let box = unbox(view, 0);
+		if (!box) return null;
+
+		let offset = box.end;
+		while ((box = unbox(view, offset))) {
+			if (box.type === 'meta') {
+				offset = box.start + 4; // version + flags
+			} else if (box.type === 'iprp' || box.type === 'ipco') {
+				offset = box.start;
+			} else if (box.type === 'ispe') {
+				return [view.getUint32(box.start + 4), view.getUint32(box.start + 8)];
+			} else if (box.type === 'mdat') {
+				break; // mdat should be last, unlikely to find metadata past here.
+			} else {
+				offset = box.end;
+			}
+		}
+
+		return null;
+	}
+	getChannels(_buffer: Uint8Array): number {
+		return 4;
+	}
+}
+
+/**
+ * # TextureAVIF
+ *
+ * [`EXT_texture_avif`](https://github.com/KhronosGroup/glTF/tree/master/extensions/2.0/Vendor/EXT_texture_avif/)
+ * enables AVIF images for any material texture.
+ *
+ * [[include:VENDOR_EXTENSIONS_NOTE.md]]
+ *
+ * AVIF offers greatly reduced transmission size, but
+ * [requires browser support](https://caniuse.com/avif). Like PNG and JPEG, an AVIF image is
+ * *fully decompressed* when uploaded to the GPU, which increases upload time and GPU memory cost.
+ * For seamless uploads and minimal GPU memory cost, it is necessary to use a GPU texture format
+ * like Basis Universal, with the `KHR_texture_basisu` extension.
+ *
+ * Defining no {@link ExtensionProperty} types, this {@link Extension} is simply attached to the
+ * {@link Document}, and affects the entire Document by allowing use of the `image/avif` MIME type
+ * and passing AVIF image data to the {@link Texture.setImage} method. Without the Extension, the
+ * same MIME types and image data would yield an invalid glTF document, under the stricter core glTF
+ * specification.
+ *
+ * Properties:
+ * - N/A
+ *
+ * ### Example
+ *
+ * ```typescript
+ * import { TextureAVIF } from '@gltf-transform/extensions';
+ *
+ * // Create an Extension attached to the Document.
+ * const avifExtension = document.createExtension(TextureAVIF)
+ * 	.setRequired(true);
+ * document.createTexture('MyAVIFTexture')
+ * 	.setMimeType('image/avif')
+ * 	.setImage(fs.readFileSync('my-texture.avif'));
+ * ```
+ *
+ * AVIF conversion is not done automatically when adding the extension as shown above — you must
+ * convert the image data first, then pass the `.avif` payload to {@link Texture.setImage}.
+ *
+ * When the `EXT_texture_avif` extension is added to a file by glTF-Transform, the extension should
+ * always be required. This tool does not support writing assets that "fall back" to optional PNG or
+ * JPEG image data.
+ */
+export class EXTTextureAVIF extends Extension {
+	public readonly extensionName = NAME;
+	/** @hidden */
+	public readonly prereadTypes = [PropertyType.TEXTURE];
+	public static readonly EXTENSION_NAME = NAME;
+
+	/** @hidden */
+	public static register(): void {
+		ImageUtils.registerFormat('image/avif', new AVIFImageUtils());
+	}
+
+	/** @hidden */
+	public preread(context: ReaderContext): this {
+		const textureDefs = context.jsonDoc.json.textures || [];
+		textureDefs.forEach((textureDef) => {
+			if (textureDef.extensions && textureDef.extensions[NAME]) {
+				textureDef.source = (textureDef.extensions[NAME] as { source: number }).source;
+			}
+		});
+		return this;
+	}
+
+	/** @hidden */
+	// eslint-disable-next-line @typescript-eslint/no-unused-vars
+	public read(context: ReaderContext): this {
+		return this;
+	}
+
+	/** @hidden */
+	public write(context: WriterContext): this {
+		const jsonDoc = context.jsonDoc;
+
+		this.document
+			.getRoot()
+			.listTextures()
+			.forEach((texture) => {
+				if (texture.getMimeType() === 'image/avif') {
+					const imageIndex = context.imageIndexMap.get(texture);
+					const textureDefs = jsonDoc.json.textures || [];
+					textureDefs.forEach((textureDef) => {
+						if (textureDef.source === imageIndex) {
+							textureDef.extensions = textureDef.extensions || {};
+							textureDef.extensions[NAME] = { source: textureDef.source };
+							delete textureDef.source;
+						}
+					});
+				}
+			});
+
+		return this;
+	}
+}
+
+interface IBox {
+	type: string;
+	start: number;
+	end: number;
+}
+
+function unbox(data: DataView, offset: number): IBox | null {
+	if (data.byteLength < 4 + offset) return null;
+
+	// size includes first 4 bytes (length)
+	const size = data.getUint32(offset);
+	if (data.byteLength < size + offset || size < 8) return null;
+
+	return {
+		type: BufferUtils.decodeText(new Uint8Array(data.buffer, data.byteOffset + offset + 4, 4)),
+		start: offset + 8,
+		end: offset + size,
+	};
+}
diff --git a/packages/extensions/src/ext-texture-webp/texture-webp.ts b/packages/extensions/src/ext-texture-webp/texture-webp.ts
index 9b32bbdc2..76714a736 100644
--- a/packages/extensions/src/ext-texture-webp/texture-webp.ts
+++ b/packages/extensions/src/ext-texture-webp/texture-webp.ts
@@ -67,8 +67,8 @@ class WEBPImageUtils implements ImageUtilsFormat {
  *
  * [[include:_VENDOR_EXTENSIONS.md]]
  *
- * WebP typically provides the minimal transmission
- * size, but [requires browser support](https://caniuse.com/webp). Like PNG and JPEG, a WebP image is
+ * WebP offers greatly reduced transmission size, but
+ * [requires browser support](https://caniuse.com/webp). Like PNG and JPEG, a WebP image is
  * *fully decompressed* when uploaded to the GPU, which increases upload time and GPU memory cost.
  * For seamless uploads and minimal GPU memory cost, it is necessary to use a GPU texture format
  * like Basis Universal, with the `KHR_texture_basisu` extension.
diff --git a/packages/extensions/src/extensions.ts b/packages/extensions/src/extensions.ts
index 552088a87..2e8b63ced 100644
--- a/packages/extensions/src/extensions.ts
+++ b/packages/extensions/src/extensions.ts
@@ -2,6 +2,7 @@
 
 import { EXTMeshGPUInstancing } from './ext-mesh-gpu-instancing';
 import { EXTMeshoptCompression } from './ext-meshopt-compression';
+import { EXTTextureAVIF } from './ext-texture-avif';
 import { EXTTextureWebP } from './ext-texture-webp';
 import { KHRDracoMeshCompression } from './khr-draco-mesh-compression';
 import { KHRLightsPunctual } from './khr-lights-punctual';
@@ -41,10 +42,17 @@ export const KHRONOS_EXTENSIONS = [
 	KHRXMP,
 ];
 
-export const ALL_EXTENSIONS = [EXTMeshGPUInstancing, EXTMeshoptCompression, EXTTextureWebP, ...KHRONOS_EXTENSIONS];
+export const ALL_EXTENSIONS = [
+	EXTMeshGPUInstancing,
+	EXTMeshoptCompression,
+	EXTTextureAVIF,
+	EXTTextureWebP,
+	...KHRONOS_EXTENSIONS,
+];
 
 export * from './ext-mesh-gpu-instancing';
 export * from './ext-meshopt-compression';
+export * from './ext-texture-avif';
 export * from './ext-texture-webp';
 export * from './khr-draco-mesh-compression';
 export * from './khr-lights-punctual';
diff --git a/packages/extensions/test/in/test.avif b/packages/extensions/test/in/test.avif
new file mode 100644
index 000000000..b10da706f
Binary files /dev/null and b/packages/extensions/test/in/test.avif differ
diff --git a/packages/extensions/test/texture-avif.test.ts b/packages/extensions/test/texture-avif.test.ts
new file mode 100644
index 000000000..7358f7840
--- /dev/null
+++ b/packages/extensions/test/texture-avif.test.ts
@@ -0,0 +1,61 @@
+import test from 'ava';
+import { Document, GLTF, ImageUtils, JSONDocument, NodeIO } from '@gltf-transform/core';
+import { EXTTextureAVIF } from '@gltf-transform/extensions';
+import path, { dirname } from 'path';
+import fs from 'fs';
+import { fileURLToPath } from 'url';
+
+const WRITER_OPTIONS = { basename: 'extensionTest' };
+
+const io = new NodeIO().registerExtensions([EXTTextureAVIF]);
+const __dirname = dirname(fileURLToPath(import.meta.url));
+
+test('@gltf-transform/extensions::texture-avif', async (t) => {
+	const doc = new Document();
+	doc.createBuffer();
+	const avifExtension = doc.createExtension(EXTTextureAVIF);
+	const tex1 = doc.createTexture('AVIFTexture').setMimeType('image/avif').setImage(new Uint8Array(10));
+	const tex2 = doc.createTexture('PNGTexture').setMimeType('image/png').setImage(new Uint8Array(15));
+	doc.createMaterial().setBaseColorTexture(tex1).setEmissiveTexture(tex2);
+
+	let jsonDoc: JSONDocument;
+
+	jsonDoc = await io.writeJSON(doc, WRITER_OPTIONS);
+
+	// Writing to file.
+	t.deepEqual(jsonDoc.json.extensionsUsed, ['EXT_texture_avif'], 'writes extensionsUsed');
+	t.is(jsonDoc.json.textures[0].source, undefined, 'omits .source on AVIF texture');
+	t.is(jsonDoc.json.textures[1].source, 1, 'includes .source on PNG texture');
+	t.is(
+		(jsonDoc.json.textures[0].extensions['EXT_texture_avif'] as GLTF.ITexture).source,
+		0,
+		'includes .source on AVIF extension'
+	);
+
+	// Read (roundtrip) from file.
+	const rtDoc = await io.readJSON(jsonDoc);
+	const rtRoot = rtDoc.getRoot();
+	t.is(rtRoot.listTextures()[0].getMimeType(), 'image/avif', 'reads AVIF mimetype');
+	t.is(rtRoot.listTextures()[1].getMimeType(), 'image/png', 'reads PNG mimetype');
+	t.is(rtRoot.listTextures()[0].getImage().byteLength, 10, 'reads AVIF payload');
+	t.is(rtRoot.listTextures()[1].getImage().byteLength, 15, 'reads PNG payload');
+
+	// Clean up extension data, revert to core glTF.
+	avifExtension.dispose();
+	tex1.dispose();
+	jsonDoc = await io.writeJSON(doc, WRITER_OPTIONS);
+	t.is(jsonDoc.json.extensionsUsed, undefined, 'clears extensionsUsed');
+	t.is(jsonDoc.json.textures.length, 1, 'writes only 1 texture');
+	t.is(jsonDoc.json.textures[0].source, 0, 'includes .source on PNG texture');
+});
+
+test('@gltf-transform/core::image-utils | avif', (t) => {
+	const avif = fs.readFileSync(path.join(__dirname, 'in', 'test.avif'));
+	const buffer = new Uint8Array([0, 1, 2, 3]);
+
+	t.is(ImageUtils.getSize(new Uint8Array(8), 'image/avif'), null, 'invalid');
+	t.is(ImageUtils.getSize(buffer, 'image/avif'), null, 'no size');
+	t.deepEqual(ImageUtils.getSize(avif, 'image/avif'), [256, 256], 'size');
+	t.is(ImageUtils.getChannels(avif, 'image/avif'), 4, 'channels');
+	t.is(ImageUtils.getGPUByteLength(avif, 'image/avif'), 349524, 'gpuSize');
+});
diff --git a/packages/functions/src/texture-compress.ts b/packages/functions/src/texture-compress.ts
index c48d61bd3..835831d7b 100644
--- a/packages/functions/src/texture-compress.ts
+++ b/packages/functions/src/texture-compress.ts
@@ -9,7 +9,7 @@ import { TextureResizeFilter } from './texture-resize';
 const NAME = 'textureCompress';
 
 type Format = (typeof FORMATS)[number];
-const FORMATS = ['jpeg', 'png', 'webp'] as const;
+const FORMATS = ['jpeg', 'png', 'webp', 'avif'] as const;
 const SUPPORTED_MIME_TYPES = ['image/jpeg', 'image/png', 'image/webp'];
 
 export interface TextureCompressOptions {