diff --git a/backport-changelog/7.0/10868.md b/backport-changelog/7.0/10868.md
index 9045022e44e641..5eab0bfe57231b 100644
--- a/backport-changelog/7.0/10868.md
+++ b/backport-changelog/7.0/10868.md
@@ -1,3 +1,4 @@
 https://github.com/WordPress/wordpress-develop/pull/10868
 
 * https://github.com/WordPress/gutenberg/pull/74909
+* https://github.com/WordPress/gutenberg/pull/75112
diff --git a/lib/compat/wordpress-6.9/rest-api.php b/lib/compat/wordpress-6.9/rest-api.php
index 994d3fb000b721..f206371fc14bd7 100644
--- a/lib/compat/wordpress-6.9/rest-api.php
+++ b/lib/compat/wordpress-6.9/rest-api.php
@@ -42,7 +42,7 @@ function gutenberg_rest_theme_export_link_rel( $response, $theme ) {
  * @return array Modified array of arguments.
  */
 function gutenberg_override_attachments_rest_controller( $args, $post_type ) {
-	if ( 'attachment' === $post_type && ! gutenberg_is_experiment_enabled( 'gutenberg-media-processing' ) ) {
+	if ( 'attachment' === $post_type && ! gutenberg_is_client_side_media_processing_enabled() ) {
 		$args['rest_controller_class'] = 'Gutenberg_REST_Attachments_Controller_6_9';
 	}
 	return $args;
diff --git a/lib/compat/wordpress-7.0/media.php b/lib/compat/wordpress-7.0/media.php
new file mode 100644
index 00000000000000..cbd5d70598e71b
--- /dev/null
+++ b/lib/compat/wordpress-7.0/media.php
@@ -0,0 +1,27 @@
+<?php
+/**
+ * Client-side media processing functions.
+ *
+ * @package gutenberg
+ */
+
+/**
+ * Checks whether client-side media processing is enabled.
+ *
+ * Client-side media processing uses the browser's capabilities to handle
+ * tasks like image resizing and compression before uploading to the server.
+ *
+ * @since 20.8.0
+ *
+ * @return bool Whether client-side media processing is enabled.
+ */
+function gutenberg_is_client_side_media_processing_enabled() {
+	/**
+	 * Filters whether client-side media processing is enabled.
+	 *
+	 * @since 20.8.0
+	 *
+	 * @param bool $enabled Whether client-side media processing is enabled. Default true.
+	 */
+	return apply_filters( 'wp_client_side_media_processing_enabled', true );
+}
diff --git a/lib/experimental/editor-settings.php b/lib/experimental/editor-settings.php
index 901f7745143b08..77fb2be07bcaf4 100644
--- a/lib/experimental/editor-settings.php
+++ b/lib/experimental/editor-settings.php
@@ -22,9 +22,6 @@ function gutenberg_enable_experiments() {
 	if ( $gutenberg_experiments && array_key_exists( 'gutenberg-dataviews-media-modal', $gutenberg_experiments ) ) {
 		wp_add_inline_script( 'wp-block-editor', 'window.__experimentalDataViewsMediaModal = true', 'before' );
 	}
-	if ( $gutenberg_experiments && array_key_exists( 'gutenberg-media-processing', $gutenberg_experiments ) ) {
-		wp_add_inline_script( 'wp-block-editor', 'window.__experimentalMediaProcessing = true', 'before' );
-	}
 	if ( $gutenberg_experiments && array_key_exists( 'gutenberg-content-only-inspector-fields', $gutenberg_experiments ) ) {
 		wp_add_inline_script( 'wp-block-editor', 'window.__experimentalContentOnlyInspectorFields = true', 'before' );
 	}
diff --git a/lib/experiments-page.php b/lib/experiments-page.php
index 588c35ae54a624..eb28c2a51838b1 100644
--- a/lib/experiments-page.php
+++ b/lib/experiments-page.php
@@ -113,18 +113,6 @@ function gutenberg_initialize_experiments_settings() {
 		)
 	);
 
-	add_settings_field(
-		'gutenberg-media-processing',
-		__( 'Client-side media processing', 'gutenberg' ),
-		'gutenberg_display_experiment_field',
-		'gutenberg-experiments',
-		'gutenberg_experiments_section',
-		array(
-			'label' => __( 'Enables client-side media processing to leverage the browser\'s capabilities to handle tasks like image resizing and compression.', 'gutenberg' ),
-			'id'    => 'gutenberg-media-processing',
-		)
-	);
-
 	add_settings_field(
 		'gutenberg-color-randomizer',
 		__( 'Color randomizer', 'gutenberg' ),
diff --git a/lib/load.php b/lib/load.php
index 36da6f88e32f81..5b0674274a2063 100644
--- a/lib/load.php
+++ b/lib/load.php
@@ -108,6 +108,7 @@ function gutenberg_is_experiment_enabled( $name ) {
 require __DIR__ . '/compat/wordpress-7.0/auto-register.php';
 require __DIR__ . '/compat/wordpress-7.0/blocks.php';
 require __DIR__ . '/compat/wordpress-7.0/kses.php';
+require __DIR__ . '/compat/wordpress-7.0/media.php';
 
 // Experimental features.
 require __DIR__ . '/experimental/block-editor-settings-mobile.php';
@@ -189,9 +190,7 @@ function gutenberg_is_experiment_enabled( $name ) {
 require __DIR__ . '/block-supports/custom-css.php';
 
 // Client-side media processing.
-if ( gutenberg_is_experiment_enabled( 'gutenberg-media-processing' ) ) {
-	require_once __DIR__ . '/experimental/media/load.php';
-}
+require_once __DIR__ . '/media/load.php';
 
 // Interactivity API full-page client-side navigation.
 if ( gutenberg_is_experiment_enabled( 'gutenberg-full-page-client-side-navigation' ) ) {
diff --git a/lib/experimental/media/class-gutenberg-rest-attachments-controller.php b/lib/media/class-gutenberg-rest-attachments-controller.php
similarity index 98%
rename from lib/experimental/media/class-gutenberg-rest-attachments-controller.php
rename to lib/media/class-gutenberg-rest-attachments-controller.php
index 3eb40bcf8dd16c..60b2930bec9b6e 100644
--- a/lib/experimental/media/class-gutenberg-rest-attachments-controller.php
+++ b/lib/media/class-gutenberg-rest-attachments-controller.php
@@ -2,11 +2,14 @@
 /**
  * Class Gutenberg_REST_Attachments_Controller.
  *
- * @package MediaExperiments
+ * @package gutenberg
  */
 
 /**
- * Class Gutenberg_REST_Attachments_Controller.
+ * REST API controller for media attachments.
+ *
+ * Extends the core attachments controller to add client-side media processing
+ * functionality including sideload support and sub-size generation control.
  */
 class Gutenberg_REST_Attachments_Controller extends WP_REST_Attachments_Controller {
 	/**
diff --git a/lib/experimental/media/docs/client-side-media-docs.md b/lib/media/docs/client-side-media-docs.md
similarity index 100%
rename from lib/experimental/media/docs/client-side-media-docs.md
rename to lib/media/docs/client-side-media-docs.md
diff --git a/lib/experimental/media/load.php b/lib/media/load.php
similarity index 91%
rename from lib/experimental/media/load.php
rename to lib/media/load.php
index 5e7b00173ca616..6d2cf05561d821 100644
--- a/lib/experimental/media/load.php
+++ b/lib/media/load.php
@@ -1,10 +1,25 @@
 <?php
 /**
- * Adds media-related experimental functionality.
+ * Adds media-related functionality for client-side media processing.
  *
  * @package gutenberg
  */
 
+if ( ! gutenberg_is_client_side_media_processing_enabled() ) {
+	return;
+}
+
+/**
+ * Sets a global JS variable to indicate that client-side media processing is enabled.
+ */
+function gutenberg_set_client_side_media_processing_flag() {
+	if ( ! gutenberg_is_client_side_media_processing_enabled() ) {
+		return;
+	}
+	wp_add_inline_script( 'wp-block-editor', 'window.__clientSideMediaProcessing = true', 'before' );
+}
+add_action( 'admin_init', 'gutenberg_set_client_side_media_processing_flag' );
+
 /**
  * Returns a list of all available image sizes.
  *
@@ -195,9 +210,9 @@ function gutenberg_rest_get_attachment_filesize( array $post ): ?int {
  * @return string Filtered rewrite rules.
  */
 function gutenberg_filter_mod_rewrite_rules( string $rules ): string {
-	$rules .= "\n# BEGIN Gutenberg client-side media processing experiment\n" .
+	$rules .= "\n# BEGIN Gutenberg client-side media processing\n" .
 				"AddType application/wasm wasm\n" .
-				"# END Gutenberg client-side media processing experiment\n";
+				"# END Gutenberg client-side media processing\n";
 
 	return $rules;
 }
@@ -213,6 +228,12 @@ function gutenberg_filter_mod_rewrite_rules( string $rules ): string {
  * @link https://web.dev/coop-coep/
  */
 function gutenberg_set_up_cross_origin_isolation() {
+	// Re-check the filter at action time, since other plugins (loaded after Gutenberg)
+	// may have added a filter to disable client-side media processing.
+	if ( ! gutenberg_is_client_side_media_processing_enabled() ) {
+		return;
+	}
+
 	$screen = get_current_screen();
 
 	if ( ! $screen ) {
diff --git a/packages/block-editor/src/components/provider/index.js b/packages/block-editor/src/components/provider/index.js
index f7fce8d2264c4a..a4ebeed9ab2459 100644
--- a/packages/block-editor/src/components/provider/index.js
+++ b/packages/block-editor/src/components/provider/index.js
@@ -41,7 +41,7 @@ let isClientSideMediaEnabledCache = null;
  * Checks if client-side media processing should be enabled.
  *
  * Returns true only if:
- * 1. The experimental media processing flag is enabled
+ * 1. The client-side media processing flag is enabled
  * 2. The browser supports WebAssembly, SharedArrayBuffer, cross-origin isolation, and CSP allows blob workers
  *
  * The result is cached for the session to ensure stability during React renders.
@@ -54,8 +54,8 @@ function shouldEnableClientSideMediaProcessing() {
 		return isClientSideMediaEnabledCache;
 	}
 
-	// Check if experimental flag is enabled first.
-	if ( ! window.__experimentalMediaProcessing ) {
+	// Check if the client-side media processing flag is enabled first.
+	if ( ! window.__clientSideMediaProcessing ) {
 		isClientSideMediaEnabledCache = false;
 		return false;
 	}
diff --git a/packages/block-library/src/image/edit.js b/packages/block-library/src/image/edit.js
index 45e4ce558d6e83..c0c67908b227b6 100644
--- a/packages/block-library/src/image/edit.js
+++ b/packages/block-library/src/image/edit.js
@@ -348,7 +348,7 @@ export function ImageEdit( {
 
 	const isSideloading = useSelect(
 		( select ) => {
-			if ( ! window.__experimentalMediaProcessing || ! id ) {
+			if ( ! window.__clientSideMediaProcessing || ! id ) {
 				return false;
 			}
 			return select( uploadStore ).isUploadingById( id );
diff --git a/packages/e2e-tests/plugins/disable-client-side-media-processing.php b/packages/e2e-tests/plugins/disable-client-side-media-processing.php
new file mode 100644
index 00000000000000..bb81e54f7cc1bc
--- /dev/null
+++ b/packages/e2e-tests/plugins/disable-client-side-media-processing.php
@@ -0,0 +1,10 @@
+<?php
+/**
+ * Plugin Name: Gutenberg Test Plugin: Disable Client-Side Media Processing
+ * Plugin URI: https://github.com/WordPress/gutenberg
+ * Author: Gutenberg Team
+ *
+ * @package gutenberg-test-disable-client-side-media-processing
+ */
+
+add_filter( 'wp_client_side_media_processing_enabled', '__return_false' );
diff --git a/packages/edit-post/src/index.js b/packages/edit-post/src/index.js
index b01fa693ed5a7c..39975131294dfa 100644
--- a/packages/edit-post/src/index.js
+++ b/packages/edit-post/src/index.js
@@ -74,7 +74,7 @@ export function initializeEditor(
 		isPublishSidebarEnabled: true,
 	} );
 
-	if ( window.__experimentalMediaProcessing ) {
+	if ( window.__clientSideMediaProcessing ) {
 		dispatch( preferencesStore ).setDefaults( 'core/media', {
 			requireApproval: true,
 			optimizeOnUpload: true,
diff --git a/packages/edit-site/src/index.js b/packages/edit-site/src/index.js
index 5bb10f3eb98973..bd62a7ad41b254 100644
--- a/packages/edit-site/src/index.js
+++ b/packages/edit-site/src/index.js
@@ -75,7 +75,7 @@ export function initializeEditor( id, settings ) {
 		enableChoosePatternModal: true,
 	} );
 
-	if ( window.__experimentalMediaProcessing ) {
+	if ( window.__clientSideMediaProcessing ) {
 		dispatch( preferencesStore ).setDefaults( 'core/media', {
 			requireApproval: true,
 			optimizeOnUpload: true,
diff --git a/packages/editor/src/components/preferences-modal/index.js b/packages/editor/src/components/preferences-modal/index.js
index e24afbb1996c38..5a64e1bb6e2541 100644
--- a/packages/editor/src/components/preferences-modal/index.js
+++ b/packages/editor/src/components/preferences-modal/index.js
@@ -298,7 +298,7 @@ function PreferencesModalContents( { extraSections = {} } ) {
 						</>
 					),
 				},
-				window.__experimentalMediaProcessing && {
+				window.__clientSideMediaProcessing && {
 					name: 'media',
 					tabLabel: __( 'Media' ),
 					content: (
diff --git a/packages/editor/src/components/provider/use-upload-save-lock.js b/packages/editor/src/components/provider/use-upload-save-lock.js
index c4acc9cc315dfc..8c0473e061774f 100644
--- a/packages/editor/src/components/provider/use-upload-save-lock.js
+++ b/packages/editor/src/components/provider/use-upload-save-lock.js
@@ -16,19 +16,20 @@ const LOCK_NAME = 'upload-in-progress';
  * A hook that locks post saving and autosaving while media uploads are in progress.
  * This prevents users from publishing or saving while files are still uploading.
  *
- * Only active when the experimental media processing feature is enabled.
+ * Only active when client-side media processing is enabled.
  */
 export default function useUploadSaveLock() {
-	const isExperimentEnabled = window.__experimentalMediaProcessing;
+	const isClientSideMediaProcessingEnabled =
+		window.__clientSideMediaProcessing;
 
 	const isUploading = useSelect(
 		( select ) => {
-			if ( ! isExperimentEnabled ) {
+			if ( ! isClientSideMediaProcessingEnabled ) {
 				return false;
 			}
 			return select( uploadStore ).isUploading();
 		},
-		[ isExperimentEnabled ]
+		[ isClientSideMediaProcessingEnabled ]
 	);
 
 	const {
@@ -39,7 +40,7 @@ export default function useUploadSaveLock() {
 	} = useDispatch( editorStore );
 
 	useEffect( () => {
-		if ( ! isExperimentEnabled ) {
+		if ( ! isClientSideMediaProcessingEnabled ) {
 			return;
 		}
 
@@ -56,7 +57,7 @@ export default function useUploadSaveLock() {
 			unlockPostAutosaving( LOCK_NAME );
 		};
 	}, [
-		isExperimentEnabled,
+		isClientSideMediaProcessingEnabled,
 		isUploading,
 		lockPostSaving,
 		unlockPostSaving,
diff --git a/packages/editor/src/utils/media-upload/index.js b/packages/editor/src/utils/media-upload/index.js
index 26fbbf3bf128c8..2a3d4ca46f440f 100644
--- a/packages/editor/src/utils/media-upload/index.js
+++ b/packages/editor/src/utils/media-upload/index.js
@@ -62,6 +62,9 @@ export default function mediaUpload( {
 			? currentPost.id
 			: currentPost?.wp_id;
 	const setSaveLock = () => {
+		if ( window.__clientSideMediaProcessing ) {
+			return; // Skip - handled by useUploadSaveLock in editor provider
+		}
 		lockPostSaving( lockKey );
 		lockPostAutosaving( lockKey );
 		imageIsUploading = true;
@@ -69,6 +72,9 @@ export default function mediaUpload( {
 
 	const postData = currentPostId ? { post: currentPostId } : {};
 	const clearSaveLock = () => {
+		if ( window.__clientSideMediaProcessing ) {
+			return; // Skip - handled by useUploadSaveLock in editor provider
+		}
 		unlockPostSaving( lockKey );
 		unlockPostAutosaving( lockKey );
 		imageIsUploading = false;
@@ -80,7 +86,7 @@ export default function mediaUpload( {
 		onFileChange: ( file ) => {
 			// When client-side media processing is enabled, save locking
 			// is handled by useUploadSaveLock in the editor provider.
-			if ( ! window.__experimentalMediaProcessing ) {
+			if ( ! window.__clientSideMediaProcessing ) {
 				if ( ! imageIsUploading ) {
 					setSaveLock();
 				} else {
@@ -111,7 +117,7 @@ export default function mediaUpload( {
 		},
 		maxUploadFileSize,
 		onError: ( { message } ) => {
-			if ( ! window.__experimentalMediaProcessing ) {
+			if ( ! window.__clientSideMediaProcessing ) {
 				clearSaveLock();
 			}
 			onError( message );
diff --git a/packages/media-utils/src/utils/upload-media.ts b/packages/media-utils/src/utils/upload-media.ts
index 3b49e317ffb9e4..278b5c4ababf7a 100644
--- a/packages/media-utils/src/utils/upload-media.ts
+++ b/packages/media-utils/src/utils/upload-media.ts
@@ -21,7 +21,7 @@ import { UploadError } from './upload-error';
 
 declare global {
 	interface Window {
-		__experimentalMediaProcessing?: boolean;
+		__clientSideMediaProcessing?: boolean;
 	}
 }
 
@@ -82,7 +82,7 @@ export function uploadMedia( {
 	const filesSet: Array< Partial< Attachment > | null > = [];
 	const setAndUpdateFiles = ( index: number, value: Attachment | null ) => {
 		// For client-side media processing, this is handled by the upload-media package.
-		if ( ! window.__experimentalMediaProcessing ) {
+		if ( ! window.__clientSideMediaProcessing ) {
 			if ( filesSet[ index ]?.url ) {
 				revokeBlobURL( filesSet[ index ].url );
 			}
@@ -123,7 +123,7 @@ export function uploadMedia( {
 		validFiles.push( mediaFile );
 
 		// For client-side media processing, this is handled by the upload-media package.
-		if ( ! window.__experimentalMediaProcessing ) {
+		if ( ! window.__clientSideMediaProcessing ) {
 			// Set temporary URL to create placeholder media file, this is replaced
 			// with final file from media gallery when upload is `done` below.
 			filesSet.push( { url: createBlobURL( mediaFile ) } );
diff --git a/phpunit/bootstrap.php b/phpunit/bootstrap.php
index bdde8917ac192a..19667b25979b8e 100644
--- a/phpunit/bootstrap.php
+++ b/phpunit/bootstrap.php
@@ -90,7 +90,6 @@ function fail_if_died( $message ) {
 		'gutenberg-full-site-editing'  => 1,
 		'gutenberg-form-blocks'        => 1,
 		'gutenberg-block-experiments'  => 1,
-		'gutenberg-media-processing'   => 1,
 	),
 );
 
diff --git a/phpunit/experimental/media/class-gutenberg-rest-attachments-controller-test.php b/phpunit/media/class-gutenberg-rest-attachments-controller-test.php
similarity index 99%
rename from phpunit/experimental/media/class-gutenberg-rest-attachments-controller-test.php
rename to phpunit/media/class-gutenberg-rest-attachments-controller-test.php
index 6b4edf44454347..31f2b51c6eb350 100644
--- a/phpunit/experimental/media/class-gutenberg-rest-attachments-controller-test.php
+++ b/phpunit/media/class-gutenberg-rest-attachments-controller-test.php
@@ -1,4 +1,11 @@
 <?php
+/**
+ * Tests for Gutenberg_REST_Attachments_Controller.
+ *
+ * Tests the REST API controller for media attachments which provides
+ * client-side media processing functionality including sideload support
+ * and sub-size generation control.
+ */
 
 /**
  * @coversDefaultClass \Gutenberg_REST_Attachments_Controller
diff --git a/phpunit/experimental/media/media-processing-test.php b/phpunit/media/media-processing-test.php
similarity index 74%
rename from phpunit/experimental/media/media-processing-test.php
rename to phpunit/media/media-processing-test.php
index 2717d2582879ff..0208361005f4df 100644
--- a/phpunit/experimental/media/media-processing-test.php
+++ b/phpunit/media/media-processing-test.php
@@ -1,7 +1,13 @@
 <?php
 
 /**
- * Tests for experimental client-side media processing.
+ * Tests for client-side media processing.
+ *
+ * Client-side media processing is a core feature that uses the browser's
+ * capabilities to handle tasks like image resizing and compression before
+ * uploading to the server. It can be disabled via the
+ * 'wp_client_side_media_processing_enabled' filter or checked using
+ * the gutenberg_is_client_side_media_processing_enabled() helper function.
  */
 class Media_Processing_Test extends WP_UnitTestCase {
 	/**
@@ -194,4 +200,55 @@ public function test_gutenberg_override_media_templates(): void {
 		$this->assertStringContainsString( '<img crossorigin="anonymous"', $output );
 		$this->assertStringContainsString( '<video crossorigin="anonymous"', $output );
 	}
+
+	/**
+	 * Tests that client-side media processing is enabled by default.
+	 *
+	 * @covers ::gutenberg_is_client_side_media_processing_enabled
+	 */
+	public function test_client_side_media_processing_enabled_by_default() {
+		$this->assertTrue( gutenberg_is_client_side_media_processing_enabled() );
+	}
+
+	/**
+	 * Tests that client-side media processing can be disabled via filter.
+	 *
+	 * @covers ::gutenberg_is_client_side_media_processing_enabled
+	 */
+	public function test_client_side_media_processing_can_be_disabled() {
+		add_filter( 'wp_client_side_media_processing_enabled', '__return_false' );
+		$enabled = gutenberg_is_client_side_media_processing_enabled();
+		remove_filter( 'wp_client_side_media_processing_enabled', '__return_false' );
+
+		$this->assertFalse( $enabled );
+	}
+
+	/**
+	 * Tests that the 6.9 compat REST controller is used when filter disables client-side media.
+	 *
+	 * @covers ::gutenberg_override_attachments_rest_controller
+	 */
+	public function test_compat_rest_controller_used_when_filter_disabled() {
+		add_filter( 'wp_client_side_media_processing_enabled', '__return_false' );
+
+		$result = gutenberg_override_attachments_rest_controller( array(), 'attachment' );
+
+		remove_filter( 'wp_client_side_media_processing_enabled', '__return_false' );
+
+		$this->assertSame(
+			array( 'rest_controller_class' => 'Gutenberg_REST_Attachments_Controller_6_9' ),
+			$result
+		);
+	}
+
+	/**
+	 * Tests that the 6.9 compat REST controller is not used when filter is enabled (default).
+	 *
+	 * @covers ::gutenberg_override_attachments_rest_controller
+	 */
+	public function test_compat_rest_controller_not_used_when_filter_enabled() {
+		$result = gutenberg_override_attachments_rest_controller( array(), 'attachment' );
+
+		$this->assertSame( array(), $result );
+	}
 }
diff --git a/test/e2e/specs/editor/blocks/classic.spec.js b/test/e2e/specs/editor/blocks/classic.spec.js
index 620194caa7f803..4318e51fe9227f 100644
--- a/test/e2e/specs/editor/blocks/classic.spec.js
+++ b/test/e2e/specs/editor/blocks/classic.spec.js
@@ -18,14 +18,25 @@ test.use( {
 } );
 
 test.describe( 'Classic', () => {
-	test.beforeEach( async ( { admin } ) => {
-		await admin.createNewPost();
+	test.beforeAll( async ( { requestUtils } ) => {
+		// Cross-origin isolation (COEP) prevents TinyMCE from
+		// initializing properly in its iframe.
+		await requestUtils.activatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 	} );
 
 	test.afterAll( async ( { requestUtils } ) => {
+		await requestUtils.deactivatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 		await requestUtils.deleteAllMedia();
 	} );
 
+	test.beforeEach( async ( { admin } ) => {
+		await admin.createNewPost();
+	} );
+
 	test( 'should be inserted', async ( { editor, page } ) => {
 		await editor.insertBlock( { name: 'core/freeform' } );
 		await editor.canvas
@@ -70,10 +81,10 @@ test.describe( 'Classic', () => {
 			page.locator( '.media-modal .moxie-shim input[type=file]' )
 		);
 
-		// Wait for upload
+		// Wait for upload (increased timeout for client-side media processing).
 		await expect(
 			page.getByRole( 'checkbox', { name: fileName } )
-		).toBeChecked();
+		).toBeChecked( { timeout: 30_000 } );
 
 		const createGallery = page.getByRole( 'button', {
 			name: 'Create a new gallery',
diff --git a/test/e2e/specs/editor/blocks/cover.spec.js b/test/e2e/specs/editor/blocks/cover.spec.js
index 263eff2bc7fa4f..e7ba0047b88e23 100644
--- a/test/e2e/specs/editor/blocks/cover.spec.js
+++ b/test/e2e/specs/editor/blocks/cover.spec.js
@@ -57,18 +57,19 @@ test.describe( 'Cover', () => {
 			name: 'Block: Cover',
 		} );
 
-		const fileName = await coverBlockUtils.upload(
+		await coverBlockUtils.upload(
 			coverBlock.getByTestId( 'form-file-upload-input' )
 		);
-		const fileBasename = path.basename( fileName );
 
 		// Wait for the img's src attribute to be prefixed with http.
 		// Otherwise, the URL for the img src attribute starts is a placeholder
-		// beginning with `blob`.
-		await expect( async () => {
-			const src = await coverBlock.locator( 'img' ).getAttribute( 'src' );
-			expect( src.includes( fileBasename ) ).toBe( true );
-		} ).toPass();
+		// beginning with `blob`. Increased timeout for client-side media processing.
+		// With client-side processing, the filename may be changed by the server.
+		await expect( coverBlock.locator( 'img' ) ).toHaveAttribute(
+			'src',
+			/^https?:\/\//,
+			{ timeout: 30_000 }
+		);
 	} );
 
 	test( 'dims background image down by 50% with the average image color when an image is uploaded', async ( {
diff --git a/test/e2e/specs/editor/blocks/gallery.spec.js b/test/e2e/specs/editor/blocks/gallery.spec.js
index 0c73cff0348585..6e42a48935e73c 100644
--- a/test/e2e/specs/editor/blocks/gallery.spec.js
+++ b/test/e2e/specs/editor/blocks/gallery.spec.js
@@ -98,16 +98,21 @@ test.describe( 'Gallery', () => {
 		);
 		await expect( galleryBlock ).toBeVisible();
 
-		const fileName = await galleryBlockUtils.upload(
+		await galleryBlockUtils.upload(
 			galleryBlock.locator( 'data-testid=form-file-upload-input' )
 		);
 
 		const image = galleryBlock.locator( 'role=img' );
 		await expect( image ).toBeVisible();
-		await expect( image ).toHaveAttribute( 'src', new RegExp( fileName ) );
+		// Wait for upload to complete (includes client-side media processing time).
+		// With client-side processing, the filename may be changed by the server.
+		await expect( image ).toHaveAttribute( 'src', /^https?:\/\//, {
+			timeout: 30_000,
+		} );
 
+		// Check that content has a valid gallery with an image.
 		const regex = new RegExp(
-			`<!-- wp:gallery {\\"linkTo\\":\\"none\\"} -->\\s*<figure class=\\"wp-block-gallery has-nested-images columns-default is-cropped\\"><!-- wp:image {\\"id\\":\\d+,\\"sizeSlug\\":\\"(?:full|large)\\",\\"linkDestination\\":\\"none\\"} -->\\s*<figure class=\\"wp-block-image (?:size-full|size-large)\\"><img src=\\"[^"]+\/${ fileName }\.png\\" alt=\\"\\" class=\\"wp-image-\\d+\\"\/><\/figure>\\s*<!-- \/wp:image --><\/figure>\\s*<!-- \/wp:gallery -->`
+			`<!-- wp:gallery {\\"linkTo\\":\\"none\\"} -->\\s*<figure class=\\"wp-block-gallery has-nested-images columns-default is-cropped\\"><!-- wp:image {\\"id\\":\\d+,\\"sizeSlug\\":\\"(?:full|large)\\",\\"linkDestination\\":\\"none\\"} -->\\s*<figure class=\\"wp-block-image (?:size-full|size-large)\\"><img src=\\"[^"]+\\" alt=\\"\\" class=\\"wp-image-\\d+\\"\/><\/figure>\\s*<!-- \/wp:image --><\/figure>\\s*<!-- \/wp:gallery -->`
 		);
 		await expect.poll( editor.getEditedPostContent ).toMatch( regex );
 	} );
diff --git a/test/e2e/specs/editor/blocks/image.spec.js b/test/e2e/specs/editor/blocks/image.spec.js
index e0655bcbe696fa..55c920c40c5c84 100644
--- a/test/e2e/specs/editor/blocks/image.spec.js
+++ b/test/e2e/specs/editor/blocks/image.spec.js
@@ -43,7 +43,7 @@ test.describe( 'Image', () => {
 		);
 		await expect( imageBlock ).toBeVisible();
 
-		const fileName = await imageBlockUtils.upload(
+		await imageBlockUtils.upload(
 			imageBlock.locator( 'data-testid=form-file-upload-input' )
 		);
 
@@ -51,11 +51,16 @@ test.describe( 'Image', () => {
 			name: 'This image has an empty alt attribute',
 		} );
 		await expect( image ).toBeVisible();
-		await expect( image ).toHaveAttribute( 'src', new RegExp( fileName ) );
+		// Wait for upload to complete (includes client-side media processing time).
+		// With client-side processing, the filename may be changed by the server.
+		await expect( image ).toHaveAttribute( 'src', /^https?:\/\//, {
+			timeout: 30_000,
+		} );
 
+		// Check that content has a valid image block with an ID.
 		const regex = new RegExp(
 			`<!-- wp:image {"id":(\\d+),"sizeSlug":"full","linkDestination":"none"} -->
-<figure class="wp-block-image size-full"><img src="[^"]+\\/${ fileName }\\.png" alt="" class="wp-image-\\1"/></figure>
+<figure class="wp-block-image size-full"><img src="[^"]+" alt="" class="wp-image-\\1"/></figure>
 <!-- \\/wp:image -->`
 		);
 		expect( await editor.getEditedPostContent() ).toMatch( regex );
@@ -75,10 +80,13 @@ test.describe( 'Image', () => {
 			name: 'This image has an empty alt attribute',
 		} );
 
-		const fileName = await imageBlockUtils.upload(
+		await imageBlockUtils.upload(
 			imageBlock.locator( 'data-testid=form-file-upload-input' )
 		);
-		await expect( image ).toHaveAttribute( 'src', new RegExp( fileName ) );
+		// Wait for upload to complete (includes client-side media processing time).
+		await expect( image ).toHaveAttribute( 'src', /^https?:\/\//, {
+			timeout: 30_000,
+		} );
 		await editor.clickBlockToolbarButton( 'Add caption' );
 		await page.keyboard.type( '1' );
 		await page.keyboard.press( 'Enter' );
@@ -106,12 +114,15 @@ test.describe( 'Image', () => {
 			name: 'This image has an empty alt attribute',
 		} );
 
-		const fileName = await imageBlockUtils.upload(
+		await imageBlockUtils.upload(
 			imageBlock.locator( 'data-testid=form-file-upload-input' )
 		);
 
 		await expect( image ).toBeVisible();
-		await expect( image ).toHaveAttribute( 'src', new RegExp( fileName ) );
+		// Wait for upload to complete (includes client-side media processing time).
+		await expect( image ).toHaveAttribute( 'src', /^https?:\/\//, {
+			timeout: 30_000,
+		} );
 		await editor.clickBlockToolbarButton( 'Add caption' );
 		await page.keyboard.type( '12' );
 		await page.keyboard.press( 'ArrowLeft' );
@@ -139,12 +150,15 @@ test.describe( 'Image', () => {
 			name: 'This image has an empty alt attribute',
 		} );
 
-		const fileName = await imageBlockUtils.upload(
+		await imageBlockUtils.upload(
 			imageBlock.locator( 'data-testid=form-file-upload-input' )
 		);
 
 		await expect( image ).toBeVisible();
-		await expect( image ).toHaveAttribute( 'src', new RegExp( fileName ) );
+		// Wait for upload to complete (includes client-side media processing time).
+		await expect( image ).toHaveAttribute( 'src', /^https?:\/\//, {
+			timeout: 30_000,
+		} );
 
 		// Add caption and navigate to inline toolbar.
 		await editor.clickBlockToolbarButton( 'Add caption' );
@@ -200,7 +214,7 @@ test.describe( 'Image', () => {
 			return input;
 		} );
 
-		const fileName = await imageBlockUtils.upload( tmpInput );
+		await imageBlockUtils.upload( tmpInput );
 
 		const paragraphRect = await imageBlock.boundingBox();
 		const pX = paragraphRect.x + paragraphRect.width / 2;
@@ -221,7 +235,10 @@ test.describe( 'Image', () => {
 			[ tmpInput, pX, pY ]
 		);
 
-		await expect( image ).toHaveAttribute( 'src', new RegExp( fileName ) );
+		// Wait for upload to complete (includes client-side media processing time).
+		await expect( image ).toHaveAttribute( 'src', /^https?:\/\//, {
+			timeout: 30_000,
+		} );
 	} );
 
 	test( 'allows zooming using the crop tools', async ( {
@@ -240,11 +257,14 @@ test.describe( 'Image', () => {
 			name: 'This image has an empty alt attribute',
 		} );
 
-		const fileName = await imageBlockUtils.upload(
+		await imageBlockUtils.upload(
 			imageBlock.locator( 'data-testid=form-file-upload-input' )
 		);
 
-		await expect( image ).toHaveAttribute( 'src', new RegExp( fileName ) );
+		// Wait for upload to complete (includes client-side media processing time).
+		await expect( image ).toHaveAttribute( 'src', /^https?:\/\//, {
+			timeout: 30_000,
+		} );
 
 		// Assert that the image is initially unscaled and unedited.
 		const initialImageSrc = await image.getAttribute( 'src' );
@@ -308,11 +328,14 @@ test.describe( 'Image', () => {
 			name: 'This image has an empty alt attribute',
 		} );
 
-		const fileName = await imageBlockUtils.upload(
+		await imageBlockUtils.upload(
 			imageBlock.locator( 'data-testid=form-file-upload-input' )
 		);
 
-		await expect( image ).toHaveAttribute( 'src', new RegExp( fileName ) );
+		// Wait for upload to complete (includes client-side media processing time).
+		await expect( image ).toHaveAttribute( 'src', /^https?:\/\//, {
+			timeout: 30_000,
+		} );
 
 		// Assert that the image is initially unscaled and unedited.
 		const initialImageSrc = await image.getAttribute( 'src' );
@@ -367,11 +390,14 @@ test.describe( 'Image', () => {
 			name: 'This image has an empty alt attribute',
 		} );
 
-		const fileName = await imageBlockUtils.upload(
+		await imageBlockUtils.upload(
 			imageBlock.locator( 'data-testid=form-file-upload-input' )
 		);
 
-		await expect( image ).toHaveAttribute( 'src', new RegExp( fileName ) );
+		// Wait for upload to complete (includes client-side media processing time).
+		await expect( image ).toHaveAttribute( 'src', /^https?:\/\//, {
+			timeout: 30_000,
+		} );
 
 		// Rotate the image.
 		await editor.clickBlockToolbarButton( 'Crop' );
@@ -405,11 +431,14 @@ test.describe( 'Image', () => {
 			name: 'This image has an empty alt attribute',
 		} );
 
-		const fileName = await imageBlockUtils.upload(
+		await imageBlockUtils.upload(
 			imageBlock.locator( 'data-testid=form-file-upload-input' )
 		);
 
-		await expect( image ).toHaveAttribute( 'src', new RegExp( fileName ) );
+		// Wait for upload to complete (includes client-side media processing time).
+		await expect( image ).toHaveAttribute( 'src', /^https?:\/\//, {
+			timeout: 30_000,
+		} );
 		await editor.canvas.locator( '.wp-block-image' ).focus();
 		await pageUtils.pressKeys( 'primary+z' );
 
@@ -527,7 +556,7 @@ test.describe( 'Image', () => {
 		);
 		await expect( imageBlock ).toBeVisible();
 
-		const fileName = await imageBlockUtils.upload(
+		await imageBlockUtils.upload(
 			imageBlock.locator( 'data-testid=form-file-upload-input' )
 		);
 
@@ -535,10 +564,20 @@ test.describe( 'Image', () => {
 			name: 'This image has an empty alt attribute',
 		} );
 		await expect( imageInEditor ).toBeVisible();
-		await expect( imageInEditor ).toHaveAttribute(
-			'src',
-			new RegExp( fileName )
-		);
+		// Wait for upload to complete (includes client-side media processing time).
+		// With client-side processing, the filename may be changed by the server.
+		await expect( imageInEditor ).toHaveAttribute( 'src', /^https?:\/\//, {
+			timeout: 30_000,
+		} );
+		// Also wait for the is-transient class to be removed, indicating all
+		// processing (including thumbnail generation) is complete.
+		await expect( imageBlock ).not.toHaveClass( /is-transient/, {
+			timeout: 30_000,
+		} );
+		// Wait for the Publish button to be enabled (all background processing complete).
+		await expect(
+			page.getByRole( 'button', { name: 'Publish', exact: true } )
+		).toBeEnabled( { timeout: 30_000 } );
 
 		const postId = await editor.publishPost();
 		await page.goto( `/?p=${ postId }` );
@@ -548,10 +587,7 @@ test.describe( 'Image', () => {
 
 		const imageDom = figureDom.locator( 'img' );
 		await expect( imageDom ).toBeVisible();
-		await expect( imageDom ).toHaveAttribute(
-			'src',
-			new RegExp( fileName )
-		);
+		await expect( imageDom ).toHaveAttribute( 'src', /^https?:\/\// );
 	} );
 
 	test( 'image inserted via link should appear in the frontend published post content', async ( {
@@ -653,6 +689,18 @@ test.describe( 'Image', () => {
 			imageBlock.locator( 'data-testid=form-file-upload-input' )
 		);
 
+		// Wait for upload to complete (includes client-side media processing time).
+		const image = imageBlock.getByRole( 'img', {
+			name: 'This image has an empty alt attribute',
+		} );
+		await expect( image ).toHaveAttribute( 'src', /^https?:\/\//, {
+			timeout: 30_000,
+		} );
+		// Also wait for the is-transient class to be removed.
+		await expect( imageBlock ).not.toHaveClass( /is-transient/, {
+			timeout: 30_000,
+		} );
+
 		await page.getByLabel( 'Block tools' ).getByLabel( 'Link' ).click();
 
 		// This form lacks distinguishing qualities other than the
@@ -665,6 +713,11 @@ test.describe( 'Image', () => {
 
 		await form.getByRole( 'button', { name: 'Apply' } ).click();
 
+		// Wait for the Publish button to be enabled (all background processing complete).
+		await expect(
+			page.getByRole( 'button', { name: 'Publish', exact: true } )
+		).toBeEnabled( { timeout: 30_000 } );
+
 		const postId = await editor.publishPost();
 		await page.goto( `/?p=${ postId }` );
 
@@ -691,6 +744,14 @@ test.describe( 'Image', () => {
 			imageBlock.locator( 'data-testid=form-file-upload-input' )
 		);
 
+		// Wait for upload to complete (includes client-side media processing time).
+		const image = imageBlock.getByRole( 'img', {
+			name: 'This image has an empty alt attribute',
+		} );
+		await expect( image ).toHaveAttribute( 'src', /^https?:\/\//, {
+			timeout: 30_000,
+		} );
+
 		await editor.clickBlockToolbarButton( 'Link' );
 
 		const urlPopover = page.locator(
@@ -807,6 +868,14 @@ test.describe( 'Image', () => {
 			imageBlock.locator( 'data-testid=form-file-upload-input' )
 		);
 
+		// Wait for upload to complete (includes client-side media processing time).
+		const image = imageBlock.getByRole( 'img', {
+			name: 'This image has an empty alt attribute',
+		} );
+		await expect( image ).toHaveAttribute( 'src', /^https?:\/\//, {
+			timeout: 30_000,
+		} );
+
 		await page.getByLabel( 'Block tools' ).getByLabel( 'Link' ).click();
 
 		const uriInput = page.getByRole( 'combobox', {
@@ -1020,6 +1089,12 @@ test.describe( 'Image - Site editor', () => {
 	test.beforeAll( async ( { requestUtils } ) => {
 		await requestUtils.deleteAllMedia();
 		await requestUtils.activateTheme( 'emptytheme' );
+		// Client-side media processing is not yet fully supported in the
+		// site editor context (upload pipeline gets stuck). Disable it
+		// so the test can use the traditional server-side upload path.
+		await requestUtils.activatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 	} );
 
 	test.beforeEach( async ( { admin } ) => {
@@ -1035,6 +1110,9 @@ test.describe( 'Image - Site editor', () => {
 	} );
 
 	test.afterAll( async ( { requestUtils } ) => {
+		await requestUtils.deactivatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 		await requestUtils.activateTheme( 'twentytwentyone' );
 	} );
 
@@ -1049,7 +1127,7 @@ test.describe( 'Image - Site editor', () => {
 		);
 		await expect( imageBlock ).toBeVisible();
 
-		const fileName = await imageBlockUtils.upload(
+		await imageBlockUtils.upload(
 			imageBlock.locator( 'data-testid=form-file-upload-input' )
 		);
 
@@ -1057,11 +1135,16 @@ test.describe( 'Image - Site editor', () => {
 			name: 'This image has an empty alt attribute',
 		} );
 		await expect( image ).toBeVisible();
-		await expect( image ).toHaveAttribute( 'src', new RegExp( fileName ) );
 
+		// Wait for upload to complete.
+		await expect( image ).toHaveAttribute( 'src', /\/[^\s]+\.\w+$/i, {
+			timeout: 30_000,
+		} );
+
+		// Check that content has a valid image block with an ID.
 		const regex = new RegExp(
 			`<!-- wp:image {"id":(\\d+),"sizeSlug":"full","linkDestination":"none"} -->
-<figure class="wp-block-image size-full"><img src="[^"]+\\/${ fileName }\\.png" alt="" class="wp-image-\\1"/></figure>
+<figure class="wp-block-image size-full"><img src="[^"]+" alt="" class="wp-image-\\1"/></figure>
 <!-- \\/wp:image -->`
 		);
 		expect( await editor.getEditedPostContent() ).toMatch( regex );
diff --git a/test/e2e/specs/editor/plugins/block-context.spec.js b/test/e2e/specs/editor/plugins/block-context.spec.js
index ab16d904dcffd9..5406239a038e7b 100644
--- a/test/e2e/specs/editor/plugins/block-context.spec.js
+++ b/test/e2e/specs/editor/plugins/block-context.spec.js
@@ -5,6 +5,9 @@ const { test, expect } = require( '@wordpress/e2e-test-utils-playwright' );
 
 test.describe( 'Block context', () => {
 	test.beforeAll( async ( { requestUtils } ) => {
+		await requestUtils.activatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 		await requestUtils.activatePlugin( 'gutenberg-test-block-context' );
 	} );
 
@@ -14,6 +17,9 @@ test.describe( 'Block context', () => {
 
 	test.afterAll( async ( { requestUtils } ) => {
 		await requestUtils.deactivatePlugin( 'gutenberg-test-block-context' );
+		await requestUtils.deactivatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 	} );
 
 	test( 'Block context propagates to inner blocks', async ( { editor } ) => {
diff --git a/test/e2e/specs/editor/plugins/iframed-block.spec.js b/test/e2e/specs/editor/plugins/iframed-block.spec.js
index 0b5343169d5bf8..70b06bd82aae02 100644
--- a/test/e2e/specs/editor/plugins/iframed-block.spec.js
+++ b/test/e2e/specs/editor/plugins/iframed-block.spec.js
@@ -4,6 +4,18 @@
 const { test, expect } = require( '@wordpress/e2e-test-utils-playwright' );
 
 test.describe( 'Iframed block', () => {
+	test.beforeAll( async ( { requestUtils } ) => {
+		await requestUtils.activatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
+	} );
+
+	test.afterAll( async ( { requestUtils } ) => {
+		await requestUtils.deactivatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
+	} );
+
 	test.beforeEach( async ( { requestUtils, admin } ) => {
 		await requestUtils.activatePlugin( 'gutenberg-test-iframed-block' );
 		await admin.createNewPost( { postType: 'page' } );
diff --git a/test/e2e/specs/editor/plugins/iframed-inline-styles.spec.js b/test/e2e/specs/editor/plugins/iframed-inline-styles.spec.js
index 8fa4cbffa9df8c..3e69ef7a04920a 100644
--- a/test/e2e/specs/editor/plugins/iframed-inline-styles.spec.js
+++ b/test/e2e/specs/editor/plugins/iframed-inline-styles.spec.js
@@ -5,6 +5,9 @@ const { test, expect } = require( '@wordpress/e2e-test-utils-playwright' );
 
 test.describe( 'iframed inline styles', () => {
 	test.beforeAll( async ( { requestUtils } ) => {
+		await requestUtils.activatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 		await requestUtils.activatePlugin(
 			'gutenberg-test-iframed-inline-styles'
 		);
@@ -14,6 +17,9 @@ test.describe( 'iframed inline styles', () => {
 		await requestUtils.deactivatePlugin(
 			'gutenberg-test-iframed-inline-styles'
 		);
+		await requestUtils.deactivatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 	} );
 
 	test( 'should load inline styles in iframe', async ( {
diff --git a/test/e2e/specs/editor/plugins/iframed-masonry-block.spec.js b/test/e2e/specs/editor/plugins/iframed-masonry-block.spec.js
index edc6b0a68cd4ab..a8120b112a1097 100644
--- a/test/e2e/specs/editor/plugins/iframed-masonry-block.spec.js
+++ b/test/e2e/specs/editor/plugins/iframed-masonry-block.spec.js
@@ -5,6 +5,9 @@ const { test, expect } = require( '@wordpress/e2e-test-utils-playwright' );
 
 test.describe( 'iframed masonry block', () => {
 	test.beforeAll( async ( { requestUtils } ) => {
+		await requestUtils.activatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 		await requestUtils.activatePlugin(
 			'gutenberg-test-iframed-masonry-block'
 		);
@@ -18,6 +21,9 @@ test.describe( 'iframed masonry block', () => {
 		await requestUtils.deactivatePlugin(
 			'gutenberg-test-iframed-masonry-block'
 		);
+		await requestUtils.deactivatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 	} );
 
 	test( 'should load script and dependencies in iframe', async ( {
diff --git a/test/e2e/specs/editor/plugins/iframed-multiple-block-stylesheets.spec.js b/test/e2e/specs/editor/plugins/iframed-multiple-block-stylesheets.spec.js
index 2e6f5b6b0cb6a0..96f9f121070bdd 100644
--- a/test/e2e/specs/editor/plugins/iframed-multiple-block-stylesheets.spec.js
+++ b/test/e2e/specs/editor/plugins/iframed-multiple-block-stylesheets.spec.js
@@ -5,6 +5,9 @@ const { test, expect } = require( '@wordpress/e2e-test-utils-playwright' );
 
 test.describe( 'iframed multiple block stylesheets', () => {
 	test.beforeAll( async ( { requestUtils } ) => {
+		await requestUtils.activatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 		await requestUtils.activatePlugin(
 			'gutenberg-test-iframed-multiple-stylesheets'
 		);
@@ -18,6 +21,9 @@ test.describe( 'iframed multiple block stylesheets', () => {
 		await requestUtils.deactivatePlugin(
 			'gutenberg-test-iframed-multiple-stylesheets'
 		);
+		await requestUtils.deactivatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 	} );
 
 	test( 'should load multiple block stylesheets in iframe', async ( {
diff --git a/test/e2e/specs/editor/plugins/meta-attribute-block.spec.js b/test/e2e/specs/editor/plugins/meta-attribute-block.spec.js
index f7207178dfc706..d5810c91a146bc 100644
--- a/test/e2e/specs/editor/plugins/meta-attribute-block.spec.js
+++ b/test/e2e/specs/editor/plugins/meta-attribute-block.spec.js
@@ -10,6 +10,9 @@ const VARIATIONS = [
 
 test.describe( 'Block with a meta attribute', () => {
 	test.beforeAll( async ( { requestUtils } ) => {
+		await requestUtils.activatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 		await requestUtils.activatePlugin(
 			'gutenberg-test-meta-attribute-block'
 		);
@@ -19,6 +22,9 @@ test.describe( 'Block with a meta attribute', () => {
 		await requestUtils.deactivatePlugin(
 			'gutenberg-test-meta-attribute-block'
 		);
+		await requestUtils.deactivatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 	} );
 
 	for ( const [ title, blockName ] of VARIATIONS ) {
diff --git a/test/e2e/specs/editor/plugins/wp-editor-meta-box.spec.js b/test/e2e/specs/editor/plugins/wp-editor-meta-box.spec.js
index ad40d96b32b431..97c531ebd1c78c 100644
--- a/test/e2e/specs/editor/plugins/wp-editor-meta-box.spec.js
+++ b/test/e2e/specs/editor/plugins/wp-editor-meta-box.spec.js
@@ -8,12 +8,20 @@ test.describe( 'WP Editor Meta Boxes', () => {
 		await requestUtils.activatePlugin(
 			'gutenberg-test-plugin-wp-editor-meta-box'
 		);
+		// Cross-origin isolation (COEP) prevents TinyMCE from
+		// initializing properly in its iframe.
+		await requestUtils.activatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 	} );
 
 	test.afterAll( async ( { requestUtils } ) => {
 		await requestUtils.deactivatePlugin(
 			'gutenberg-test-plugin-wp-editor-meta-box'
 		);
+		await requestUtils.deactivatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 	} );
 
 	test( 'Should save the changes', async ( { admin, editor, page } ) => {
diff --git a/test/e2e/specs/editor/various/autocomplete-and-mentions.spec.js b/test/e2e/specs/editor/various/autocomplete-and-mentions.spec.js
index fe5c644357a724..52b314d2ad330b 100644
--- a/test/e2e/specs/editor/various/autocomplete-and-mentions.spec.js
+++ b/test/e2e/specs/editor/various/autocomplete-and-mentions.spec.js
@@ -49,6 +49,9 @@ const userList = [
 ];
 test.describe( 'Autocomplete (@firefox, @webkit)', () => {
 	test.beforeAll( async ( { requestUtils } ) => {
+		await requestUtils.activatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 		await Promise.all(
 			userList.map( ( user ) =>
 				requestUtils.createUser( {
@@ -65,6 +68,9 @@ test.describe( 'Autocomplete (@firefox, @webkit)', () => {
 		await requestUtils.deleteAllUsers();
 		await requestUtils.deactivatePlugin( 'gutenberg-test-autocompleter' );
 		await requestUtils.activateTheme( 'twentytwentyone' );
+		await requestUtils.deactivatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 	} );
 
 	test.beforeEach( async ( { admin } ) => {
diff --git a/test/e2e/specs/editor/various/big-image-size-threshold.spec.js b/test/e2e/specs/editor/various/big-image-size-threshold.spec.js
new file mode 100644
index 00000000000000..30239f121c7e38
--- /dev/null
+++ b/test/e2e/specs/editor/various/big-image-size-threshold.spec.js
@@ -0,0 +1,248 @@
+/**
+ * External dependencies
+ */
+const path = require( 'path' );
+const fs = require( 'fs/promises' );
+const os = require( 'os' );
+const { v4: uuid } = require( 'uuid' );
+
+/**
+ * WordPress dependencies
+ */
+const { test, expect } = require( '@wordpress/e2e-test-utils-playwright' );
+
+/**
+ * @typedef {import('@playwright/test').Page} Page
+ */
+
+test.use( {
+	imageBlockUtils: async ( { page }, use ) => {
+		await use( new ImageBlockUtils( { page } ) );
+	},
+} );
+
+test.describe( 'Big image size threshold', () => {
+	test.beforeAll( async ( { requestUtils } ) => {
+		await requestUtils.deleteAllMedia();
+	} );
+
+	test.beforeEach( async ( { admin } ) => {
+		await admin.createNewPost();
+	} );
+
+	test.afterEach( async ( { requestUtils } ) => {
+		await requestUtils.deleteAllMedia();
+	} );
+
+	test( 'should scale down images larger than the threshold', async ( {
+		page,
+		editor,
+		imageBlockUtils,
+		requestUtils,
+	} ) => {
+		// Skip if cross-origin isolation is not enabled.
+		// The vips library requires SharedArrayBuffer which needs cross-origin isolation.
+		const isCrossOriginIsolated = await page.evaluate(
+			() => window.crossOriginIsolated
+		);
+		// eslint-disable-next-line playwright/no-skipped-test
+		test.skip(
+			! isCrossOriginIsolated,
+			'Cross-origin isolation headers not configured on server'
+		);
+
+		// Verify the big image size threshold setting is available.
+		const threshold = await page.evaluate( () =>
+			window.wp.data
+				.select( 'core' )
+				.getEntityRecord( 'root', '__unstableBase' )
+		);
+		expect( threshold?.image_size_threshold ).toBeDefined();
+
+		await editor.insertBlock( { name: 'core/image' } );
+
+		const imageBlock = editor.canvas.locator(
+			'role=document[name="Block: Image"i]'
+		);
+		await expect( imageBlock ).toBeVisible();
+
+		// Upload a large image (3200x2400) that exceeds the default threshold (2560).
+		await imageBlockUtils.upload(
+			imageBlock.locator( 'data-testid=form-file-upload-input' ),
+			'3200x2400_e2e_test_image_responsive_lightbox.jpeg'
+		);
+
+		// Wait for the upload to complete.
+		const image = imageBlock.getByRole( 'img', {
+			name: 'This image has an empty alt attribute',
+		} );
+		await expect( image ).toBeVisible();
+
+		// Wait for the image URL to be updated to the final uploaded URL.
+		await page.waitForFunction(
+			() => {
+				const uploadStore =
+					window.wp.data.select( 'core/upload-media' );
+				if ( ! uploadStore ) {
+					return true; // Store not available, upload happened server-side.
+				}
+				const items = uploadStore.getItems();
+				return items.length === 0;
+			},
+			{ timeout: 120000 }
+		);
+
+		// Get the image ID from the block.
+		const imageId = await page.evaluate(
+			() =>
+				window.wp.data.select( 'core/block-editor' ).getSelectedBlock()
+					?.attributes?.id
+		);
+
+		if ( imageId ) {
+			// Fetch the attachment details from the REST API.
+			const media = await requestUtils.rest( {
+				method: 'GET',
+				path: `/wp/v2/media/${ imageId }`,
+			} );
+
+			// The image should be scaled down (either client-side or server-side).
+			expect( media.media_details.width ).toBeLessThanOrEqual( 2560 );
+			expect( media.media_details.height ).toBeLessThanOrEqual( 2560 );
+
+			if ( media.source_url.includes( '-scaled' ) ) {
+				// When client-side scaling adds the -scaled suffix,
+				// original_image may or may not be set depending on whether
+				// the server also processes the image. Only check if present.
+				if ( media.media_details.original_image ) {
+					expect( media.media_details.original_image ).toBeDefined();
+				}
+
+				// Verify thumbnails were generated.
+				const sizes = media.media_details.sizes;
+				expect( sizes ).toBeDefined();
+
+				// Check that at least some standard sizes were created.
+				// The exact sizes depend on theme/site configuration.
+				const hasStandardSizes =
+					sizes.thumbnail || sizes.medium || sizes.large;
+				expect( hasStandardSizes ).toBeTruthy();
+
+				// If thumbnail exists, verify it has reasonable dimensions.
+				// Default thumbnail size is 150x150.
+				if ( sizes.thumbnail ) {
+					expect( sizes.thumbnail.width ).toBeLessThanOrEqual( 150 );
+					expect( sizes.thumbnail.height ).toBeLessThanOrEqual( 150 );
+				}
+
+				// If medium exists, verify dimensions.
+				// Default medium size is 300x300.
+				if ( sizes.medium ) {
+					expect( sizes.medium.width ).toBeLessThanOrEqual( 300 );
+					expect( sizes.medium.height ).toBeLessThanOrEqual( 300 );
+				}
+			}
+		}
+	} );
+
+	test( 'should not scale images smaller than the threshold', async ( {
+		page,
+		editor,
+		imageBlockUtils,
+		requestUtils,
+	} ) => {
+		// Skip if cross-origin isolation is not enabled.
+		const isCrossOriginIsolated = await page.evaluate(
+			() => window.crossOriginIsolated
+		);
+		// eslint-disable-next-line playwright/no-skipped-test
+		test.skip(
+			! isCrossOriginIsolated,
+			'Cross-origin isolation headers not configured on server'
+		);
+
+		await editor.insertBlock( { name: 'core/image' } );
+
+		const imageBlock = editor.canvas.locator(
+			'role=document[name="Block: Image"i]'
+		);
+		await expect( imageBlock ).toBeVisible();
+
+		// Upload a small image (1024x768) that is below the default threshold (2560).
+		await imageBlockUtils.upload(
+			imageBlock.locator( 'data-testid=form-file-upload-input' ),
+			'1024x768_e2e_test_image_size.jpeg'
+		);
+
+		// Wait for the upload to complete.
+		const image = imageBlock.getByRole( 'img', {
+			name: 'This image has an empty alt attribute',
+		} );
+		await expect( image ).toBeVisible();
+
+		// Wait for the upload queue to be empty.
+		await page.waitForFunction(
+			() => {
+				const uploadStore =
+					window.wp.data.select( 'core/upload-media' );
+				if ( ! uploadStore ) {
+					return true;
+				}
+				const items = uploadStore.getItems();
+				return items.length === 0;
+			},
+			{ timeout: 120000 }
+		);
+
+		// Get the image ID from the block.
+		const imageId = await page.evaluate(
+			() =>
+				window.wp.data.select( 'core/block-editor' ).getSelectedBlock()
+					?.attributes?.id
+		);
+
+		if ( imageId ) {
+			// Fetch the attachment details from the REST API.
+			const media = await requestUtils.rest( {
+				method: 'GET',
+				path: `/wp/v2/media/${ imageId }`,
+			} );
+
+			// The image should NOT be scaled since it's below the threshold.
+			expect( media.source_url ).not.toContain( '-scaled' );
+			// Original dimensions should be preserved.
+			expect( media.media_details.width ).toBe( 1024 );
+			expect( media.media_details.height ).toBe( 768 );
+		}
+	} );
+} );
+
+class ImageBlockUtils {
+	constructor( { page } ) {
+		/** @type {Page} */
+		this.page = page;
+		this.basePath = path.join( __dirname, '..', '..', '..', 'assets' );
+
+		this.TEST_IMAGE_FILE_PATH = path.join(
+			this.basePath,
+			'10x10_e2e_test_image_z9T8jK.png'
+		);
+	}
+
+	async upload( inputElement, customFile = null ) {
+		const tmpDirectory = await fs.mkdtemp(
+			path.join( os.tmpdir(), 'gutenberg-test-image-' )
+		);
+		const fileName = uuid();
+		const extension = customFile ? path.extname( customFile ) : '.png';
+		const tmpFileName = path.join( tmpDirectory, fileName + extension );
+		const filePath = customFile
+			? path.join( this.basePath, customFile )
+			: this.TEST_IMAGE_FILE_PATH;
+		await fs.copyFile( filePath, tmpFileName );
+
+		await inputElement.setInputFiles( tmpFileName );
+
+		return fileName;
+	}
+}
diff --git a/test/e2e/specs/editor/various/cross-origin-isolation.spec.js b/test/e2e/specs/editor/various/cross-origin-isolation.spec.js
index 6f9ee94ce75ac4..77480feedccdc1 100644
--- a/test/e2e/specs/editor/various/cross-origin-isolation.spec.js
+++ b/test/e2e/specs/editor/various/cross-origin-isolation.spec.js
@@ -40,45 +40,40 @@ test.describe( 'Cross-origin isolation', () => {
 		await admin.createNewPost();
 	} );
 
-	test( 'should not affect embed previews when not cross-origin isolated', async ( {
-		page,
-		editor,
-		embedUtils,
-	} ) => {
-		// Verify that cross-origin isolation is NOT enabled (default state).
+	test( 'should be cross-origin isolated by default', async ( { page } ) => {
+		// Verify that cross-origin isolation IS enabled (default state
+		// now that client-side media processing is graduated).
 		const isCrossOriginIsolated = await page.evaluate(
 			() => window.crossOriginIsolated
 		);
-		expect( isCrossOriginIsolated ).toBe( false );
+		expect( isCrossOriginIsolated ).toBe( true );
+	} );
 
+	test( 'should render embed previews when cross-origin isolated', async ( {
+		editor,
+		embedUtils,
+	} ) => {
 		await embedUtils.interceptRequests( {
 			'https://twitter.com/notnownikki': MOCK_EMBED_RICH_SUCCESS_RESPONSE,
 		} );
 
 		await embedUtils.insertEmbed( 'https://twitter.com/notnownikki' );
 
-		// Verify the embed iframe is visible (previewable should be true by default).
+		// Verify the embed iframe is visible.
 		const embedBlock = editor.canvas
 			.getByRole( 'document', { name: 'Block' } )
 			.last();
 		const iframe = embedBlock.locator( 'iframe' );
 		await expect(
 			iframe,
-			'Embed should render iframe when not cross-origin isolated'
+			'Embed should render iframe when cross-origin isolated'
 		).toHaveAttribute( 'title', 'Embedded content from twitter.com' );
 	} );
 
-	test( 'should render video embeds with aspect ratio when not cross-origin isolated', async ( {
-		page,
+	test( 'should render video embeds with aspect ratio when cross-origin isolated', async ( {
 		editor,
 		embedUtils,
 	} ) => {
-		// Verify that cross-origin isolation is NOT enabled.
-		const isCrossOriginIsolated = await page.evaluate(
-			() => window.crossOriginIsolated
-		);
-		expect( isCrossOriginIsolated ).toBe( false );
-
 		await embedUtils.interceptRequests( {
 			'https://www.youtube.com/watch?v=lXMskKTw3Bc':
 				MOCK_EMBED_VIDEO_SUCCESS_RESPONSE,
@@ -98,117 +93,89 @@ test.describe( 'Cross-origin isolation', () => {
 		).toHaveClass( /wp-embed-aspect-16-9/ );
 	} );
 
-	/**
-	 * Tests for cross-origin isolated environment.
-	 *
-	 * These tests require the WordPress server to be configured with:
-	 * - Cross-Origin-Opener-Policy: same-origin
-	 * - Cross-Origin-Embedder-Policy: credentialless (or require-corp for Safari)
-	 *
-	 * When cross-origin isolated:
-	 * - Embeds should have `crossorigin="anonymous"` attribute
-	 * - Iframes should have `credentialless` attribute (when supported)
-	 * - Embeds from non-previewable providers (facebook, smugmug) should show placeholder
-	 */
-	test.describe( 'when cross-origin isolated', () => {
-		// Skip these tests if cross-origin isolation is not enabled.
-		test.beforeEach( async ( { page } ) => {
-			const isCrossOriginIsolated = await page.evaluate(
-				() => window.crossOriginIsolated
-			);
-			test.skip(
-				! isCrossOriginIsolated,
-				'Cross-origin isolation headers not configured on server'
-			);
+	test( 'should add crossorigin attribute to embed iframes', async ( {
+		editor,
+		embedUtils,
+	} ) => {
+		await embedUtils.interceptRequests( {
+			'https://twitter.com/notnownikki': MOCK_EMBED_RICH_SUCCESS_RESPONSE,
 		} );
 
-		test( 'should add crossorigin attribute to embed iframes', async ( {
-			editor,
-			embedUtils,
-		} ) => {
-			await embedUtils.interceptRequests( {
-				'https://twitter.com/notnownikki':
-					MOCK_EMBED_RICH_SUCCESS_RESPONSE,
-			} );
-
-			await embedUtils.insertEmbed( 'https://twitter.com/notnownikki' );
-
-			const embedBlock = editor.canvas
-				.getByRole( 'document', { name: 'Block' } )
-				.last();
-			const iframe = embedBlock.locator( 'iframe.components-sandbox' );
-
-			await expect(
-				iframe,
-				'Embed iframe should have crossorigin attribute'
-			).toHaveAttribute( 'crossorigin', 'anonymous' );
-		} );
+		await embedUtils.insertEmbed( 'https://twitter.com/notnownikki' );
+
+		const embedBlock = editor.canvas
+			.getByRole( 'document', { name: 'Block' } )
+			.last();
+		const iframe = embedBlock.locator( 'iframe.components-sandbox' );
+
+		await expect(
+			iframe,
+			'Embed iframe should have crossorigin attribute'
+		).toHaveAttribute( 'crossorigin', 'anonymous' );
+	} );
+
+	test( 'should add credentialless attribute to embed iframes when supported', async ( {
+		page,
+		editor,
+		embedUtils,
+	} ) => {
+		// Check if browser supports credentialless iframes.
+		const supportsCredentialless = await page.evaluate(
+			() => 'credentialless' in window.HTMLIFrameElement.prototype
+		);
 
-		test( 'should add credentialless attribute to embed iframes when supported', async ( {
-			page,
-			editor,
-			embedUtils,
-		} ) => {
-			// Check if browser supports credentialless iframes.
-			const supportsCredentialless = await page.evaluate(
-				() => 'credentialless' in window.HTMLIFrameElement.prototype
-			);
-
-			test.skip(
-				! supportsCredentialless,
-				'Browser does not support credentialless iframes'
-			);
-
-			await embedUtils.interceptRequests( {
-				'https://twitter.com/notnownikki':
-					MOCK_EMBED_RICH_SUCCESS_RESPONSE,
-			} );
-
-			await embedUtils.insertEmbed( 'https://twitter.com/notnownikki' );
-
-			const embedBlock = editor.canvas
-				.getByRole( 'document', { name: 'Block' } )
-				.last();
-			const iframe = embedBlock.locator( 'iframe.components-sandbox' );
-
-			await expect(
-				iframe,
-				'Embed iframe should have credentialless attribute'
-			).toHaveAttribute( 'credentialless', '' );
+		test.skip(
+			! supportsCredentialless,
+			'Browser does not support credentialless iframes'
+		);
+
+		await embedUtils.interceptRequests( {
+			'https://twitter.com/notnownikki': MOCK_EMBED_RICH_SUCCESS_RESPONSE,
 		} );
 
-		test( 'should show placeholder for denylisted providers when credentialless not supported', async ( {
-			page,
-			editor,
-			embedUtils,
-		} ) => {
-			// This test only applies when credentialless is NOT supported.
-			const supportsCredentialless = await page.evaluate(
-				() => 'credentialless' in window.HTMLIFrameElement.prototype
-			);
-
-			test.skip(
-				supportsCredentialless,
-				'Browser supports credentialless iframes'
-			);
-
-			await embedUtils.interceptRequests( {
-				'https://twitter.com/notnownikki':
-					MOCK_EMBED_RICH_SUCCESS_RESPONSE,
-			} );
-
-			await embedUtils.insertEmbed( 'https://twitter.com/notnownikki' );
-
-			const embedBlock = editor.canvas
-				.getByRole( 'document', { name: 'Block' } )
-				.last();
-
-			// When credentialless is not supported, embeds should show a placeholder.
-			await expect(
-				embedBlock.locator( '.components-placeholder__error' ),
-				'Should show placeholder when credentialless not supported'
-			).toContainText( "can't be previewed" );
+		await embedUtils.insertEmbed( 'https://twitter.com/notnownikki' );
+
+		const embedBlock = editor.canvas
+			.getByRole( 'document', { name: 'Block' } )
+			.last();
+		const iframe = embedBlock.locator( 'iframe.components-sandbox' );
+
+		await expect(
+			iframe,
+			'Embed iframe should have credentialless attribute'
+		).toHaveAttribute( 'credentialless', '' );
+	} );
+
+	test( 'should show placeholder for denylisted providers when credentialless not supported', async ( {
+		page,
+		editor,
+		embedUtils,
+	} ) => {
+		// This test only applies when credentialless is NOT supported.
+		const supportsCredentialless = await page.evaluate(
+			() => 'credentialless' in window.HTMLIFrameElement.prototype
+		);
+
+		test.skip(
+			supportsCredentialless,
+			'Browser supports credentialless iframes'
+		);
+
+		await embedUtils.interceptRequests( {
+			'https://twitter.com/notnownikki': MOCK_EMBED_RICH_SUCCESS_RESPONSE,
 		} );
+
+		await embedUtils.insertEmbed( 'https://twitter.com/notnownikki' );
+
+		const embedBlock = editor.canvas
+			.getByRole( 'document', { name: 'Block' } )
+			.last();
+
+		// When credentialless is not supported, embeds should show a placeholder.
+		await expect(
+			embedBlock.locator( '.components-placeholder__error' ),
+			'Should show placeholder when credentialless not supported'
+		).toContainText( "can't be previewed" );
 	} );
 } );
 
diff --git a/test/e2e/specs/editor/various/patterns.spec.js b/test/e2e/specs/editor/various/patterns.spec.js
index c00203af600325..aeb3fa7986c194 100644
--- a/test/e2e/specs/editor/various/patterns.spec.js
+++ b/test/e2e/specs/editor/various/patterns.spec.js
@@ -5,10 +5,21 @@ const { test, expect } = require( '@wordpress/e2e-test-utils-playwright' );
 
 test.describe( 'Unsynced pattern', () => {
 	test.beforeAll( async ( { requestUtils } ) => {
+		// Cross-origin isolation (COEP) prevents page navigations
+		// from working properly during pattern editing.
+		await requestUtils.activatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 		await requestUtils.deleteAllBlocks();
 		await requestUtils.deleteAllPatternCategories();
 	} );
 
+	test.afterAll( async ( { requestUtils } ) => {
+		await requestUtils.deactivatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
+	} );
+
 	test.beforeEach( async ( { admin } ) => {
 		await admin.createNewPost();
 	} );
@@ -560,6 +571,11 @@ test.describe( 'Unsynced pattern', () => {
 
 test.describe( 'Synced pattern', () => {
 	test.beforeAll( async ( { requestUtils } ) => {
+		// Cross-origin isolation (COEP) prevents page navigations
+		// from working properly during pattern editing.
+		await requestUtils.activatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 		await requestUtils.deleteAllBlocks();
 		await requestUtils.deleteAllPatternCategories();
 	} );
@@ -568,6 +584,12 @@ test.describe( 'Synced pattern', () => {
 		await admin.createNewPost();
 	} );
 
+	test.afterAll( async ( { requestUtils } ) => {
+		await requestUtils.deactivatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
+	} );
+
 	test.afterEach( async ( { requestUtils } ) => {
 		await requestUtils.deleteAllPosts();
 		await requestUtils.deleteAllBlocks();
diff --git a/test/e2e/specs/editor/various/post-editor-template-mode.spec.js b/test/e2e/specs/editor/various/post-editor-template-mode.spec.js
index facb214f29e9f4..b8924f02dd12c0 100644
--- a/test/e2e/specs/editor/various/post-editor-template-mode.spec.js
+++ b/test/e2e/specs/editor/various/post-editor-template-mode.spec.js
@@ -23,6 +23,11 @@ test.use( {
 test.describe( 'Post Editor Template mode', () => {
 	test.beforeAll( async ( { requestUtils } ) => {
 		await requestUtils.activatePlugin( 'gutenberg-test-block-templates' );
+		// Cross-origin isolation (COEP) prevents page navigations
+		// from working properly during template creation.
+		await requestUtils.activatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 	} );
 
 	test.afterEach( async ( { requestUtils } ) => {
@@ -35,6 +40,9 @@ test.describe( 'Post Editor Template mode', () => {
 	test.afterAll( async ( { requestUtils } ) => {
 		await requestUtils.activateTheme( 'twentytwentyone' );
 		await requestUtils.deactivatePlugin( 'gutenberg-test-block-templates' );
+		await requestUtils.deactivatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 	} );
 
 	test( 'Allow to switch to template mode, edit the template and check the result', async ( {
diff --git a/test/e2e/specs/editor/various/preview.spec.js b/test/e2e/specs/editor/various/preview.spec.js
index e15f143983b742..affe2486a4b4a1 100644
--- a/test/e2e/specs/editor/various/preview.spec.js
+++ b/test/e2e/specs/editor/various/preview.spec.js
@@ -10,6 +10,20 @@ test.use( {
 } );
 
 test.describe( 'Preview', () => {
+	test.beforeAll( async ( { requestUtils } ) => {
+		// Cross-origin isolation (COOP: same-origin) prevents the editor
+		// from reusing the preview popup window, breaking preview navigation.
+		await requestUtils.activatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
+	} );
+
+	test.afterAll( async ( { requestUtils } ) => {
+		await requestUtils.deactivatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
+	} );
+
 	test.beforeEach( async ( { admin } ) => {
 		await admin.createNewPost();
 	} );
@@ -215,6 +229,18 @@ test.describe( 'Preview', () => {
 } );
 
 test.describe( 'Preview with Custom Fields enabled', () => {
+	test.beforeAll( async ( { requestUtils } ) => {
+		await requestUtils.activatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
+	} );
+
+	test.afterAll( async ( { requestUtils } ) => {
+		await requestUtils.deactivatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
+	} );
+
 	test.beforeEach( async ( { admin, previewUtils } ) => {
 		await admin.createNewPost();
 		await previewUtils.toggleCustomFieldsOption( true );
diff --git a/test/e2e/specs/site-editor/site-editor-url-navigation.spec.js b/test/e2e/specs/site-editor/site-editor-url-navigation.spec.js
index 8c67eb184a39ec..307853a860ea80 100644
--- a/test/e2e/specs/site-editor/site-editor-url-navigation.spec.js
+++ b/test/e2e/specs/site-editor/site-editor-url-navigation.spec.js
@@ -6,10 +6,18 @@ const { test, expect } = require( '@wordpress/e2e-test-utils-playwright' );
 test.describe( 'Site editor url navigation', () => {
 	test.beforeAll( async ( { requestUtils } ) => {
 		await requestUtils.activateTheme( 'emptytheme' );
+		// Cross-origin isolation (COEP) prevents page navigations
+		// from working properly during template creation.
+		await requestUtils.activatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 	} );
 
 	test.afterAll( async ( { requestUtils } ) => {
 		await requestUtils.activateTheme( 'twentytwentyone' );
+		await requestUtils.deactivatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 	} );
 
 	test.beforeEach( async ( { requestUtils } ) => {
diff --git a/test/e2e/specs/site-editor/template-revert.spec.js b/test/e2e/specs/site-editor/template-revert.spec.js
index 50a5598f400ebd..f9132f22a25992 100644
--- a/test/e2e/specs/site-editor/template-revert.spec.js
+++ b/test/e2e/specs/site-editor/template-revert.spec.js
@@ -14,11 +14,19 @@ test.describe( 'Template Revert', () => {
 		await requestUtils.activateTheme( 'emptytheme' );
 		await requestUtils.deleteAllTemplates( 'wp_template' );
 		await requestUtils.deleteAllTemplates( 'wp_template_part' );
+		// Cross-origin isolation (COEP) prevents page navigations
+		// from working properly during template creation.
+		await requestUtils.activatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 	} );
 	test.afterAll( async ( { requestUtils } ) => {
 		await requestUtils.deleteAllTemplates( 'wp_template' );
 		await requestUtils.deleteAllTemplates( 'wp_template_part' );
 		await requestUtils.activateTheme( 'twentytwentyone' );
+		await requestUtils.deactivatePlugin(
+			'gutenberg-test-plugin-disable-client-side-media-processing'
+		);
 	} );
 	test.beforeEach( async ( { admin, requestUtils } ) => {
 		await requestUtils.deleteAllTemplates( 'wp_template' );