diff --git a/backport-changelog/7.0/11277.md b/backport-changelog/7.0/11277.md
new file mode 100644
index 00000000000000..9ecc1be43a3381
--- /dev/null
+++ b/backport-changelog/7.0/11277.md
@@ -0,0 +1,3 @@
+https://github.com/WordPress/wordpress-develop/pull/11277
+
+* https://github.com/WordPress/gutenberg/pull/76549
diff --git a/lib/compat/wordpress-7.0/preload.php b/lib/compat/wordpress-7.0/preload.php
index 0c650114cb2a1a..5b1d0fb14e813c 100644
--- a/lib/compat/wordpress-7.0/preload.php
+++ b/lib/compat/wordpress-7.0/preload.php
@@ -44,7 +44,7 @@ function gutenberg_block_editor_preload_paths_root_fields( $paths ) {
 	// Complete list of fields expected by packages/core-data/src/entities.js.
 	// This must match exactly for preloading to work (same fields, same order).
 	// @see packages/core-data/src/entities.js rootEntitiesConfig.__unstableBase
-	$root_fields = 'description,gmt_offset,home,image_sizes,image_size_threshold,image_output_formats,jpeg_interlaced,png_interlaced,gif_interlaced,name,site_icon,site_icon_url,site_logo,timezone_string,url,page_for_posts,page_on_front,show_on_front';
+	$root_fields = 'description,gmt_offset,home,image_sizes,image_size_threshold,image_output_formats,jpeg_interlaced,png_interlaced,gif_interlaced,client_side_supported_mime_types,name,site_icon,site_icon_url,site_logo,timezone_string,url,page_for_posts,page_on_front,show_on_front';
 
 	foreach ( $paths as $key => $path ) {
 		if ( is_string( $path ) && str_starts_with( $path, '/?_fields=' ) ) {
diff --git a/lib/media/class-gutenberg-rest-attachments-controller.php b/lib/media/class-gutenberg-rest-attachments-controller.php
index d2032ca271fa46..fb45b4ac7b73d5 100644
--- a/lib/media/class-gutenberg-rest-attachments-controller.php
+++ b/lib/media/class-gutenberg-rest-attachments-controller.php
@@ -41,16 +41,21 @@ public function register_routes(): void {
 					'callback'            => array( $this, 'sideload_item' ),
 					'permission_callback' => array( $this, 'sideload_item_permissions_check' ),
 					'args'                => array(
-						'id'         => array(
+						'id'           => array(
 							'description' => __( 'Unique identifier for the attachment.', 'gutenberg' ),
 							'type'        => 'integer',
 						),
-						'image_size' => array(
+						'image_size'   => array(
 							'description' => __( 'Image size.', 'gutenberg' ),
 							'type'        => 'string',
 							'enum'        => $valid_image_sizes,
 							'required'    => true,
 						),
+						'replace_file' => array(
+							'description' => __( 'Whether to replace the main attached file and delete the old one.', 'gutenberg' ),
+							'type'        => 'boolean',
+							'default'     => false,
+						),
 					),
 				),
 				'allow_batch' => $this->allow_batch,
@@ -408,7 +413,32 @@ public function sideload_item( WP_REST_Request $request ) {
 			$metadata = array();
 		}
 
-		if ( 'original' === $image_size ) {
+		if ( ! empty( $request['replace_file'] ) ) {
+			// Replace the main attached file with the sideloaded one.
+			$old_path = get_attached_file( $attachment_id );
+
+			update_attached_file( $attachment_id, $path );
+
+			$metadata['file'] = _wp_relative_upload_path( $path );
+
+			// Store the new file as original_image if subsizes exist.
+			if ( ! empty( $metadata['sizes'] ) ) {
+				$metadata['original_image'] = wp_basename( $path );
+			}
+
+			// Update the post MIME type to match the new file.
+			wp_update_post(
+				array(
+					'ID'             => $attachment_id,
+					'post_mime_type' => $type,
+				)
+			);
+
+			// Delete the old main file if it differs from the new one.
+			if ( $old_path && $old_path !== $path && file_exists( $old_path ) ) {
+				wp_delete_file( $old_path );
+			}
+		} elseif ( 'original' === $image_size ) {
 			$metadata['original_image'] = wp_basename( $path );
 		} elseif ( 'scaled' === $image_size ) {
 			// The current attached file is the original; record it as original_image.
diff --git a/lib/media/load.php b/lib/media/load.php
index 15e47a1b007151..cfe9dc82d4c8bc 100644
--- a/lib/media/load.php
+++ b/lib/media/load.php
@@ -86,13 +86,29 @@ function gutenberg_media_processing_filter_rest_index( WP_REST_Response $respons
 	/** This filter is documented in wp-includes/class-wp-image-editor-imagick.php */
 	$gif_interlaced = (bool) apply_filters( 'image_save_progressive', false, 'image/gif' ); // phpcs:ignore WordPress.NamingConventions.PrefixAllGlobals.NonPrefixedHooknameFound
 
+	/**
+	 * Filters the MIME types supported by client-side media processing.
+	 *
+	 * Allows plugins to add or remove MIME types from the list of formats
+	 * that can be processed client-side using WebAssembly-based vips.
+	 *
+	 * @since 21.8.0
+	 *
+	 * @param string[] $mime_types Array of MIME type strings.
+	 */
+	$client_side_supported_mime_types = apply_filters(
+		'client_side_supported_mime_types',
+		array( 'image/jpeg', 'image/png', 'image/gif', 'image/webp', 'image/avif' )
+	);
+
 	if ( current_user_can( 'upload_files' ) ) {
-		$response->data['image_sizes']          = gutenberg_get_all_image_sizes();
-		$response->data['image_size_threshold'] = $image_size_threshold;
-		$response->data['image_output_formats'] = (object) $default_image_output_formats;
-		$response->data['jpeg_interlaced']      = $jpeg_interlaced;
-		$response->data['png_interlaced']       = $png_interlaced;
-		$response->data['gif_interlaced']       = $gif_interlaced;
+		$response->data['image_sizes']                      = gutenberg_get_all_image_sizes();
+		$response->data['image_size_threshold']             = $image_size_threshold;
+		$response->data['image_output_formats']             = (object) $default_image_output_formats;
+		$response->data['jpeg_interlaced']                  = $jpeg_interlaced;
+		$response->data['png_interlaced']                   = $png_interlaced;
+		$response->data['gif_interlaced']                   = $gif_interlaced;
+		$response->data['client_side_supported_mime_types'] = $client_side_supported_mime_types;
 	}
 
 	return $response;
diff --git a/packages/block-editor/src/components/provider/use-media-upload-settings.js b/packages/block-editor/src/components/provider/use-media-upload-settings.js
index 7c00c145d27a72..0c3bbdad18aa99 100644
--- a/packages/block-editor/src/components/provider/use-media-upload-settings.js
+++ b/packages/block-editor/src/components/provider/use-media-upload-settings.js
@@ -19,6 +19,7 @@ function useMediaUploadSettings( settings = {} ) {
 			allowedMimeTypes: settings.allowedMimeTypes,
 			allImageSizes: settings.allImageSizes,
 			bigImageSizeThreshold: settings.bigImageSizeThreshold,
+			clientSideSupportedMimeTypes: settings.clientSideSupportedMimeTypes,
 		} ),
 		[ settings ]
 	);
diff --git a/packages/core-data/src/entities.js b/packages/core-data/src/entities.js
index 75cc7fc34faa40..b9104891a92665 100644
--- a/packages/core-data/src/entities.js
+++ b/packages/core-data/src/entities.js
@@ -54,6 +54,7 @@ export const rootEntitiesConfig = [
 				'jpeg_interlaced',
 				'png_interlaced',
 				'gif_interlaced',
+				'client_side_supported_mime_types',
 				'name',
 				'site_icon',
 				'site_icon_url',
diff --git a/packages/editor/src/components/provider/use-block-editor-settings.js b/packages/editor/src/components/provider/use-block-editor-settings.js
index 997469ba81f54a..58b46f93fa7f71 100644
--- a/packages/editor/src/components/provider/use-block-editor-settings.js
+++ b/packages/editor/src/components/provider/use-block-editor-settings.js
@@ -183,6 +183,8 @@ function useBlockEditorSettings( settings, postType, postId, renderingMode ) {
 			return {
 				allImageSizes: baseData?.image_sizes,
 				bigImageSizeThreshold: baseData?.image_size_threshold,
+				clientSideSupportedMimeTypes:
+					baseData?.client_side_supported_mime_types,
 				allowRightClickOverrides: get(
 					'core',
 					'allowRightClickOverrides'
diff --git a/packages/upload-media/src/store/private-actions.ts b/packages/upload-media/src/store/private-actions.ts
index fa22d3f61e3df4..3bdfc28e06c229 100644
--- a/packages/upload-media/src/store/private-actions.ts
+++ b/packages/upload-media/src/store/private-actions.ts
@@ -711,9 +711,10 @@ export function prepareItem( id: QueueItemId ) {
 		const settings = select.getSettings();
 
 		const isImage = file.type.startsWith( 'image/' );
-		const isVipsSupported = CLIENT_SIDE_SUPPORTED_MIME_TYPES.includes(
-			file.type
-		);
+		const supportedMimeTypes =
+			settings.clientSideSupportedMimeTypes ??
+			CLIENT_SIDE_SUPPORTED_MIME_TYPES;
+		const isVipsSupported = supportedMimeTypes.includes( file.type );
 
 		// For images that can be processed by vips, check if we need to scale down based on threshold.
 		if ( isImage && isVipsSupported ) {
diff --git a/packages/upload-media/src/store/test/actions.ts b/packages/upload-media/src/store/test/actions.ts
index d9f3072a1648a6..7fcc4115f2313f 100644
--- a/packages/upload-media/src/store/test/actions.ts
+++ b/packages/upload-media/src/store/test/actions.ts
@@ -324,6 +324,113 @@ describe( 'actions', () => {
 				true
 			);
 		} );
+
+		it( 'should use custom clientSideSupportedMimeTypes when set', async () => {
+			// Exclude AVIF from supported types.
+			unlock( registry.dispatch( uploadStore ) ).updateSettings( {
+				clientSideSupportedMimeTypes: [ 'image/jpeg', 'image/png' ],
+			} );
+
+			const avifFile = new File( [ 'avif' ], 'photo.avif', {
+				lastModified: 1234567891,
+				type: 'image/avif',
+			} );
+
+			unlock( registry.dispatch( uploadStore ) ).addItem( {
+				file: avifFile,
+			} );
+
+			const item = unlock(
+				registry.select( uploadStore )
+			).getAllItems()[ 0 ];
+
+			await unlock( registry.dispatch( uploadStore ) ).prepareItem(
+				item.id
+			);
+
+			const updatedItem = unlock(
+				registry.select( uploadStore )
+			).getAllItems()[ 0 ];
+
+			// AVIF is excluded from custom list, so no client-side processing.
+			expect( updatedItem.operations ).toEqual(
+				expect.arrayContaining( [ OperationType.Upload ] )
+			);
+			expect( updatedItem.operations ).not.toEqual(
+				expect.arrayContaining( [ OperationType.ThumbnailGeneration ] )
+			);
+			expect( updatedItem.additionalData.generate_sub_sizes ).toBe(
+				true
+			);
+		} );
+
+		it( 'should support normally-unsupported types via clientSideSupportedMimeTypes', async () => {
+			unlock( registry.dispatch( uploadStore ) ).updateSettings( {
+				clientSideSupportedMimeTypes: [ 'image/jpeg', 'image/bmp' ],
+			} );
+
+			const bmpFile = new File( [ 'bmp' ], 'photo.bmp', {
+				lastModified: 1234567891,
+				type: 'image/bmp',
+			} );
+
+			unlock( registry.dispatch( uploadStore ) ).addItem( {
+				file: bmpFile,
+			} );
+
+			const item = unlock(
+				registry.select( uploadStore )
+			).getAllItems()[ 0 ];
+
+			await unlock( registry.dispatch( uploadStore ) ).prepareItem(
+				item.id
+			);
+
+			const updatedItem = unlock(
+				registry.select( uploadStore )
+			).getAllItems()[ 0 ];
+
+			// BMP is in custom list, so client-side processing applies.
+			expect( updatedItem.operations ).toEqual(
+				expect.arrayContaining( [
+					OperationType.Upload,
+					OperationType.ThumbnailGeneration,
+				] )
+			);
+			expect( updatedItem.additionalData.generate_sub_sizes ).toBe(
+				false
+			);
+		} );
+
+		it( 'should use default constant when clientSideSupportedMimeTypes is not set', async () => {
+			// No custom setting — defaults should apply.
+			unlock( registry.dispatch( uploadStore ) ).addItem( {
+				file: jpegFile,
+			} );
+
+			const item = unlock(
+				registry.select( uploadStore )
+			).getAllItems()[ 0 ];
+
+			await unlock( registry.dispatch( uploadStore ) ).prepareItem(
+				item.id
+			);
+
+			const updatedItem = unlock(
+				registry.select( uploadStore )
+			).getAllItems()[ 0 ];
+
+			// JPEG is in default list, so client-side processing applies.
+			expect( updatedItem.operations ).toEqual(
+				expect.arrayContaining( [
+					OperationType.Upload,
+					OperationType.ThumbnailGeneration,
+				] )
+			);
+			expect( updatedItem.additionalData.generate_sub_sizes ).toBe(
+				false
+			);
+		} );
 	} );
 
 	describe( 'cancelItem', () => {
diff --git a/packages/upload-media/src/store/types.ts b/packages/upload-media/src/store/types.ts
index 579ad27d5c7e9e..10b5df6c379b2b 100644
--- a/packages/upload-media/src/store/types.ts
+++ b/packages/upload-media/src/store/types.ts
@@ -172,6 +172,9 @@ export interface Settings {
 	bigImageSizeThreshold?: number;
 	// Map of source MIME types to output MIME types for transcoding.
 	imageOutputFormats?: Record< string, string >;
+	// MIME types supported by client-side media processing.
+	// Overrides the default CLIENT_SIDE_SUPPORTED_MIME_TYPES constant.
+	clientSideSupportedMimeTypes?: readonly string[];
 	// Whether to use progressive/interlaced encoding for JPEG.
 	jpegInterlaced?: boolean;
 	// Whether to use interlaced encoding for PNG.
diff --git a/phpunit/media/media-processing-test.php b/phpunit/media/media-processing-test.php
index a697d27897dbb9..1ffb47b7682d76 100644
--- a/phpunit/media/media-processing-test.php
+++ b/phpunit/media/media-processing-test.php
@@ -121,6 +121,7 @@ public function test_get_rest_index_should_return_additional_settings() {
 		$this->assertArrayNotHasKey( 'png_interlaced', $data );
 		$this->assertArrayNotHasKey( 'gif_interlaced', $data );
 		$this->assertArrayNotHasKey( 'image_sizes', $data );
+		$this->assertArrayNotHasKey( 'client_side_supported_mime_types', $data );
 	}
 
 	/**
@@ -141,6 +142,36 @@ public function test_get_rest_index_should_return_additional_settings_can_upload
 		$this->assertArrayHasKey( 'png_interlaced', $data );
 		$this->assertArrayHasKey( 'gif_interlaced', $data );
 		$this->assertArrayHasKey( 'image_sizes', $data );
+		$this->assertArrayHasKey( 'client_side_supported_mime_types', $data );
+		$this->assertSame(
+			array( 'image/jpeg', 'image/png', 'image/gif', 'image/webp', 'image/avif' ),
+			$data['client_side_supported_mime_types']
+		);
+	}
+
+	/**
+	 * @covers ::gutenberg_media_processing_filter_rest_index
+	 */
+	public function test_client_side_supported_mime_types_filter() {
+		wp_set_current_user( self::$admin_id );
+
+		$filter_callback = static function () {
+			return array( 'image/jpeg', 'image/png' );
+		};
+		add_filter( 'client_side_supported_mime_types', $filter_callback );
+
+		$server = new WP_REST_Server();
+
+		$request = new WP_REST_Request( 'GET', '/' );
+		$index   = $server->dispatch( $request );
+		$data    = $index->get_data();
+
+		remove_filter( 'client_side_supported_mime_types', $filter_callback );
+
+		$this->assertSame(
+			array( 'image/jpeg', 'image/png' ),
+			$data['client_side_supported_mime_types']
+		);
 	}
 
 	/**