diff --git a/packages/block-editor/src/components/block-settings-menu/block-settings-dropdown.js b/packages/block-editor/src/components/block-settings-menu/block-settings-dropdown.js
index 8bce0ae063915..9d643173c70c2 100644
--- a/packages/block-editor/src/components/block-settings-menu/block-settings-dropdown.js
+++ b/packages/block-editor/src/components/block-settings-menu/block-settings-dropdown.js
@@ -12,7 +12,11 @@ import { useSelect } from '@wordpress/data';
 import { moreVertical } from '@wordpress/icons';
 
 import { Children, cloneElement, useCallback } from '@wordpress/element';
-import { serialize, store as blocksStore } from '@wordpress/blocks';
+import {
+	serialize,
+	store as blocksStore,
+	__experimentalCloneSanitizedBlock,
+} from '@wordpress/blocks';
 import { store as keyboardShortcutsStore } from '@wordpress/keyboard-shortcuts';
 import { useCopyToClipboard } from '@wordpress/compose';
 
@@ -33,7 +37,12 @@ const POPOVER_PROPS = {
 };
 
 function CopyMenuItem( { blocks, onCopy } ) {
-	const ref = useCopyToClipboard( () => serialize( blocks ), onCopy );
+	const ref = useCopyToClipboard( () => {
+		blocks = blocks.map( ( block ) =>
+			__experimentalCloneSanitizedBlock( block )
+		);
+		return serialize( blocks );
+	}, onCopy );
 	return <MenuItem ref={ ref }>{ __( 'Copy' ) }</MenuItem>;
 }
 
diff --git a/packages/block-editor/src/components/copy-handler/index.js b/packages/block-editor/src/components/copy-handler/index.js
index 0015ea7a9b6ae..9c4e9e9105582 100644
--- a/packages/block-editor/src/components/copy-handler/index.js
+++ b/packages/block-editor/src/components/copy-handler/index.js
@@ -5,6 +5,7 @@ import { useCallback } from '@wordpress/element';
 import {
 	serialize,
 	pasteHandler,
+	__experimentalCloneSanitizedBlock,
 	store as blocksStore,
 } from '@wordpress/blocks';
 import {
@@ -121,7 +122,12 @@ export function useClipboardHandler() {
 					flashBlock( selectedBlockClientIds[ 0 ] );
 				}
 				notifyCopy( event.type, selectedBlockClientIds );
-				const blocks = getBlocksByClientId( selectedBlockClientIds );
+				let blocks = getBlocksByClientId( selectedBlockClientIds );
+				if ( event.type === 'copy' ) {
+					blocks = blocks.map( ( block ) =>
+						__experimentalCloneSanitizedBlock( block )
+					);
+				}
 				const serialized = serialize( blocks );
 
 				event.clipboardData.setData( 'text/plain', serialized );
diff --git a/packages/blocks/src/api/factory.js b/packages/blocks/src/api/factory.js
index 7937ad98fb330..78d240ce44e5a 100644
--- a/packages/blocks/src/api/factory.js
+++ b/packages/blocks/src/api/factory.js
@@ -15,6 +15,8 @@ import {
 	isFunction,
 	isEmpty,
 	map,
+	reduce,
+	omit,
 } from 'lodash';
 
 /**
@@ -32,7 +34,7 @@ import {
 } from './registration';
 import {
 	normalizeBlockType,
-	__experimentalSanitizeBlockAttributes,
+	__experimentalGetBlockAttributesNamesByRole,
 } from './utils';
 
 /**
@@ -45,9 +47,37 @@ import {
  * @return {Object} Block object.
  */
 export function createBlock( name, attributes = {}, innerBlocks = [] ) {
-	const sanitizedAttributes = __experimentalSanitizeBlockAttributes(
-		name,
-		attributes
+	// Get the type definition associated with a registered block.
+	const blockType = getBlockType( name );
+
+	if ( undefined === blockType ) {
+		throw new Error( `Block type '${ name }' is not registered.` );
+	}
+
+	const sanitizedAttributes = reduce(
+		blockType.attributes,
+		( accumulator, schema, key ) => {
+			const value = attributes[ key ];
+
+			if ( undefined !== value ) {
+				accumulator[ key ] = value;
+			} else if ( schema.hasOwnProperty( 'default' ) ) {
+				accumulator[ key ] = schema.default;
+			}
+
+			if ( [ 'node', 'children' ].indexOf( schema.source ) !== -1 ) {
+				// Ensure value passed is always an array, which we're expecting in
+				// the RichText component to handle the deprecated value.
+				if ( typeof accumulator[ key ] === 'string' ) {
+					accumulator[ key ] = [ accumulator[ key ] ];
+				} else if ( ! Array.isArray( accumulator[ key ] ) ) {
+					accumulator[ key ] = [];
+				}
+			}
+
+			return accumulator;
+		},
+		{}
 	);
 
 	const clientId = uuid();
@@ -94,8 +124,9 @@ export function createBlocksFromInnerBlocksTemplate(
 }
 
 /**
- * Given a block object, returns a copy of the block object while sanitizing its attributes,
+ * Given a block object, returns a copy of the block object,
  * optionally merging new attributes and/or replacing its inner blocks.
+ * Attributes with the `internal` role are not copied into the new object.
  *
  * @param {Object} block           Block instance.
  * @param {Object} mergeAttributes Block attributes.
@@ -110,18 +141,20 @@ export function __experimentalCloneSanitizedBlock(
 ) {
 	const clientId = uuid();
 
-	const sanitizedAttributes = __experimentalSanitizeBlockAttributes(
-		block.name,
+	// Merge in new attributes and strip out attributes with the `internal` role,
+	// which should not be copied during block duplication.
+	const filteredAttributes = omit(
 		{
 			...block.attributes,
 			...mergeAttributes,
-		}
+		},
+		__experimentalGetBlockAttributesNamesByRole( block.name, 'internal' )
 	);
 
 	return {
 		...block,
 		clientId,
-		attributes: sanitizedAttributes,
+		attributes: filteredAttributes,
 		innerBlocks:
 			newInnerBlocks ||
 			block.innerBlocks.map( ( innerBlock ) =>
diff --git a/packages/blocks/src/api/index.js b/packages/blocks/src/api/index.js
index b5ae50093233d..e57b34b4bb9a4 100644
--- a/packages/blocks/src/api/index.js
+++ b/packages/blocks/src/api/index.js
@@ -141,7 +141,6 @@ export {
 	isValidIcon,
 	getBlockLabel as __experimentalGetBlockLabel,
 	getAccessibleBlockLabel as __experimentalGetAccessibleBlockLabel,
-	__experimentalSanitizeBlockAttributes,
 	__experimentalGetBlockAttributesNamesByRole,
 } from './utils';
 
diff --git a/packages/blocks/src/api/test/factory.js b/packages/blocks/src/api/test/factory.js
index 3b4d8671f6e1b..4042f54ea99c8 100644
--- a/packages/blocks/src/api/test/factory.js
+++ b/packages/blocks/src/api/test/factory.js
@@ -90,17 +90,21 @@ describe( 'block factory', () => {
 			registerBlockType( 'core/test-block', {
 				...defaultBlockSettings,
 				attributes: {
-					content: {
+					childrenContent: {
 						type: 'array',
 						source: 'children',
 					},
+					nodeContent: {
+						source: 'node',
+					},
 				},
 			} );
 
 			const block = createBlock( 'core/test-block' );
 
 			expect( block.attributes ).toEqual( {
-				content: [],
+				childrenContent: [],
+				nodeContent: [],
 			} );
 		} );
 
@@ -177,6 +181,14 @@ describe( 'block factory', () => {
 
 			expect( block.attributes ).toEqual( {} );
 		} );
+
+		it( 'throws error if the block is not registered', () => {
+			expect( () => {
+				createBlock( 'core/not-registered-test-block', {} );
+			} ).toThrowErrorMatchingInlineSnapshot(
+				`"Block type 'core/not-registered-test-block' is not registered."`
+			);
+		} );
 	} );
 
 	describe( 'createBlocksFromInnerBlocksTemplate', () => {
@@ -428,25 +440,182 @@ describe( 'block factory', () => {
 	} );
 
 	describe( '__experimentalCloneSanitizedBlock', () => {
-		it( 'should sanitize attributes not defined in the block type', () => {
+		it( 'should not duplicate internal attributes', () => {
 			registerBlockType( 'core/test-block', {
 				...defaultBlockSettings,
 				attributes: {
-					align: {
+					internalAttribute: {
+						type: 'string',
+						__experimentalRole: 'internal',
+					},
+					contentAttribute: {
+						type: 'string',
+						__experimentalRole: 'content',
+					},
+					attributeWithNoRole: {
 						type: 'string',
 					},
 				},
 			} );
 
 			const block = createBlock( 'core/test-block', {
-				notDefined: 'not-defined',
+				internalAttribute: 'this-should-not-be-copied',
+				contentAttribute: 'some content',
+				attributeWithNoRole: 'another attribute',
+			} );
+
+			const clonedBlock = __experimentalCloneSanitizedBlock( block, {} );
+
+			expect( clonedBlock.attributes ).toEqual( {
+				contentAttribute: 'some content',
+				attributeWithNoRole: 'another attribute',
+			} );
+		} );
+
+		it( 'should merge attributes into the existing block', () => {
+			registerBlockType( 'core/test-block', {
+				attributes: {
+					align: {
+						type: 'string',
+					},
+					isDifferent: {
+						type: 'boolean',
+						default: false,
+					},
+					includesDefault: {
+						type: 'boolean',
+						default: true,
+					},
+					includesFalseyDefault: {
+						type: 'number',
+						default: 0,
+					},
+					content: {
+						type: 'array',
+						source: 'children',
+					},
+					defaultContent: {
+						type: 'array',
+						source: 'children',
+						default: 'test',
+					},
+					unknownDefaultContent: {
+						type: 'array',
+						source: 'children',
+						default: 1,
+					},
+					htmlContent: {
+						source: 'html',
+					},
+				},
+				save: noop,
+				category: 'text',
+				title: 'test block',
 			} );
+			const block = deepFreeze(
+				createBlock( 'core/test-block', { align: 'left' }, [
+					createBlock( 'core/test-block' ),
+				] )
+			);
 
 			const clonedBlock = __experimentalCloneSanitizedBlock( block, {
-				notDefined2: 'not-defined-2',
+				isDifferent: true,
+				htmlContent: 'test',
 			} );
 
-			expect( clonedBlock.attributes ).toEqual( {} );
+			expect( clonedBlock.name ).toEqual( block.name );
+			expect( clonedBlock.attributes ).toEqual( {
+				includesDefault: true,
+				includesFalseyDefault: 0,
+				align: 'left',
+				isDifferent: true,
+				content: [],
+				defaultContent: [ 'test' ],
+				unknownDefaultContent: [],
+				htmlContent: 'test',
+			} );
+			expect( clonedBlock.innerBlocks ).toHaveLength( 1 );
+			expect( typeof clonedBlock.clientId ).toBe( 'string' );
+			expect( clonedBlock.clientId ).not.toBe( block.clientId );
+		} );
+
+		it( 'should replace inner blocks of the existing block', () => {
+			registerBlockType( 'core/test-block', {
+				attributes: {
+					align: {
+						type: 'string',
+					},
+					isDifferent: {
+						type: 'boolean',
+						default: false,
+					},
+				},
+				save: noop,
+				category: 'text',
+				title: 'test block',
+			} );
+			const block = deepFreeze(
+				createBlock( 'core/test-block', { align: 'left' }, [
+					createBlock( 'core/test-block', { align: 'right' } ),
+					createBlock( 'core/test-block', { align: 'left' } ),
+				] )
+			);
+
+			const clonedBlock = __experimentalCloneSanitizedBlock(
+				block,
+				undefined,
+				[ createBlock( 'core/test-block' ) ]
+			);
+
+			expect( clonedBlock.innerBlocks ).toHaveLength( 1 );
+			expect(
+				clonedBlock.innerBlocks[ 0 ].attributes
+			).not.toHaveProperty( 'align' );
+		} );
+
+		it( 'should clone innerBlocks if innerBlocks are not passed', () => {
+			registerBlockType( 'core/test-block', {
+				attributes: {
+					align: {
+						type: 'string',
+					},
+					isDifferent: {
+						type: 'boolean',
+						default: false,
+					},
+				},
+				save: noop,
+				category: 'text',
+				title: 'test block',
+			} );
+			const block = deepFreeze(
+				createBlock( 'core/test-block', { align: 'left' }, [
+					createBlock( 'core/test-block', { align: 'right' } ),
+					createBlock( 'core/test-block', { align: 'left' } ),
+				] )
+			);
+
+			const clonedBlock = __experimentalCloneSanitizedBlock( block );
+
+			expect( clonedBlock.innerBlocks ).toHaveLength( 2 );
+			expect( clonedBlock.innerBlocks[ 0 ].clientId ).not.toBe(
+				block.innerBlocks[ 0 ].clientId
+			);
+			expect( clonedBlock.innerBlocks[ 0 ].attributes ).not.toBe(
+				block.innerBlocks[ 0 ].attributes
+			);
+			expect( clonedBlock.innerBlocks[ 0 ].attributes ).toEqual(
+				block.innerBlocks[ 0 ].attributes
+			);
+			expect( clonedBlock.innerBlocks[ 1 ].clientId ).not.toBe(
+				block.innerBlocks[ 1 ].clientId
+			);
+			expect( clonedBlock.innerBlocks[ 1 ].attributes ).not.toBe(
+				block.innerBlocks[ 1 ].attributes
+			);
+			expect( clonedBlock.innerBlocks[ 1 ].attributes ).toEqual(
+				block.innerBlocks[ 1 ].attributes
+			);
 		} );
 	} );
 
diff --git a/packages/blocks/src/api/test/utils.js b/packages/blocks/src/api/test/utils.js
index 3ffc1bf5944bc..3cf3f7b1cc51d 100644
--- a/packages/blocks/src/api/test/utils.js
+++ b/packages/blocks/src/api/test/utils.js
@@ -17,7 +17,6 @@ import {
 	isUnmodifiedDefaultBlock,
 	getAccessibleBlockLabel,
 	getBlockLabel,
-	__experimentalSanitizeBlockAttributes,
 	__experimentalGetBlockAttributesNamesByRole,
 } from '../utils';
 
@@ -215,103 +214,6 @@ describe( 'getAccessibleBlockLabel', () => {
 	} );
 } );
 
-describe( 'sanitizeBlockAttributes', () => {
-	afterEach( () => {
-		getBlockTypes().forEach( ( block ) => {
-			unregisterBlockType( block.name );
-		} );
-	} );
-
-	it( 'sanitize block attributes not defined in the block type', () => {
-		registerBlockType( 'core/test-block', {
-			attributes: {
-				defined: {
-					type: 'string',
-				},
-			},
-			title: 'Test block',
-		} );
-
-		const attributes = __experimentalSanitizeBlockAttributes(
-			'core/test-block',
-			{
-				defined: 'defined-attribute',
-				notDefined: 'not-defined-attribute',
-			}
-		);
-
-		expect( attributes ).toEqual( {
-			defined: 'defined-attribute',
-		} );
-	} );
-
-	it( 'throws error if the block is not registered', () => {
-		expect( () => {
-			__experimentalSanitizeBlockAttributes(
-				'core/not-registered-test-block',
-				{}
-			);
-		} ).toThrowErrorMatchingInlineSnapshot(
-			`"Block type 'core/not-registered-test-block' is not registered."`
-		);
-	} );
-
-	it( 'handles undefined values and default values', () => {
-		registerBlockType( 'core/test-block', {
-			attributes: {
-				hasDefaultValue: {
-					type: 'string',
-					default: 'default-value',
-				},
-				noDefaultValue: {
-					type: 'string',
-				},
-			},
-			title: 'Test block',
-		} );
-
-		const attributes = __experimentalSanitizeBlockAttributes(
-			'core/test-block',
-			{}
-		);
-
-		expect( attributes ).toEqual( {
-			hasDefaultValue: 'default-value',
-		} );
-	} );
-
-	it( 'handles node and children sources as arrays', () => {
-		registerBlockType( 'core/test-block', {
-			attributes: {
-				nodeContent: {
-					source: 'node',
-				},
-				childrenContent: {
-					source: 'children',
-				},
-				withDefault: {
-					source: 'children',
-					default: 'test',
-				},
-			},
-			title: 'Test block',
-		} );
-
-		const attributes = __experimentalSanitizeBlockAttributes(
-			'core/test-block',
-			{
-				nodeContent: [ 'test-1', 'test-2' ],
-			}
-		);
-
-		expect( attributes ).toEqual( {
-			nodeContent: [ 'test-1', 'test-2' ],
-			childrenContent: [],
-			withDefault: [ 'test' ],
-		} );
-	} );
-} );
-
 describe( '__experimentalGetBlockAttributesNamesByRole', () => {
 	beforeAll( () => {
 		registerBlockType( 'core/test-block-1', {
diff --git a/packages/blocks/src/api/utils.js b/packages/blocks/src/api/utils.js
index 1cc87b237cabd..e087484c91d6f 100644
--- a/packages/blocks/src/api/utils.js
+++ b/packages/blocks/src/api/utils.js
@@ -1,7 +1,7 @@
 /**
  * External dependencies
  */
-import { every, has, isFunction, isString, reduce, maxBy } from 'lodash';
+import { every, has, isFunction, isString, maxBy } from 'lodash';
 import { colord, extend } from 'colord';
 import namesPlugin from 'colord/plugins/names';
 import a11yPlugin from 'colord/plugins/a11y';
@@ -239,49 +239,6 @@ export function getAccessibleBlockLabel(
 	);
 }
 
-/**
- * Ensure attributes contains only values defined by block type, and merge
- * default values for missing attributes.
- *
- * @param {string} name       The block's name.
- * @param {Object} attributes The block's attributes.
- * @return {Object} The sanitized attributes.
- */
-export function __experimentalSanitizeBlockAttributes( name, attributes ) {
-	// Get the type definition associated with a registered block.
-	const blockType = getBlockType( name );
-
-	if ( undefined === blockType ) {
-		throw new Error( `Block type '${ name }' is not registered.` );
-	}
-
-	return reduce(
-		blockType.attributes,
-		( accumulator, schema, key ) => {
-			const value = attributes[ key ];
-
-			if ( undefined !== value ) {
-				accumulator[ key ] = value;
-			} else if ( schema.hasOwnProperty( 'default' ) ) {
-				accumulator[ key ] = schema.default;
-			}
-
-			if ( [ 'node', 'children' ].indexOf( schema.source ) !== -1 ) {
-				// Ensure value passed is always an array, which we're expecting in
-				// the RichText component to handle the deprecated value.
-				if ( typeof accumulator[ key ] === 'string' ) {
-					accumulator[ key ] = [ accumulator[ key ] ];
-				} else if ( ! Array.isArray( accumulator[ key ] ) ) {
-					accumulator[ key ] = [];
-				}
-			}
-
-			return accumulator;
-		},
-		{}
-	);
-}
-
 /**
  * Filter block attributes by `role` and return their names.
  *
diff --git a/packages/customize-widgets/src/filters/move-to-sidebar.js b/packages/customize-widgets/src/filters/move-to-sidebar.js
index 9e7910ce785a6..df11b6ee4942d 100644
--- a/packages/customize-widgets/src/filters/move-to-sidebar.js
+++ b/packages/customize-widgets/src/filters/move-to-sidebar.js
@@ -55,10 +55,10 @@ const withMoveToSidebarToolbarItem = createHigherOrderComponent(
 			const newSidebarControl = sidebarControls.find(
 				( sidebarControl ) => sidebarControl.id === sidebarControlId
 			);
-
-			if ( widgetId ) {
+			const activeSidebarAdapter = activeSidebarControl.sidebarAdapter;
+			if ( widgetId && activeSidebarAdapter.getWidget( widgetId ) ) {
 				/**
-				 * If there's a widgetId, move it to the other sidebar.
+				 * If there's an existing widget, move it to the other sidebar.
 				 */
 				const oldSetting = activeSidebarControl.setting;
 				const newSetting = newSidebarControl.setting;
@@ -67,15 +67,15 @@ const withMoveToSidebarToolbarItem = createHigherOrderComponent(
 				newSetting( [ ...newSetting(), widgetId ] );
 			} else {
 				/**
-				 * If there isn't a widgetId, it's most likely a inner block.
-				 * First, remove the block in the original sidebar,
+				 * If there isn't an existing widget with this id, it's most likely an
+				 * inner block. First, remove the block in the original sidebar,
 				 * then, create a new widget in the new sidebar and get back its widgetId.
 				 */
-				const sidebarAdapter = newSidebarControl.sidebarAdapter;
+				const newSidebarAdapter = newSidebarControl.sidebarAdapter;
 
 				removeBlock( clientId );
-				const addedWidgetIds = sidebarAdapter.setWidgets( [
-					...sidebarAdapter.getWidgets(),
+				const addedWidgetIds = newSidebarAdapter.setWidgets( [
+					...newSidebarAdapter.getWidgets(),
 					blockToWidget( block ),
 				] );
 				// The last non-null id is the added widget's id.
diff --git a/packages/customize-widgets/src/index.js b/packages/customize-widgets/src/index.js
index 554f19cf05122..ea679beaaaffd 100644
--- a/packages/customize-widgets/src/index.js
+++ b/packages/customize-widgets/src/index.js
@@ -8,6 +8,7 @@ import {
 	__experimentalRegisterExperimentalCoreBlocks,
 } from '@wordpress/block-library';
 import {
+	registerInternalWidgetIds,
 	registerLegacyWidgetBlock,
 	registerLegacyWidgetVariations,
 	registerWidgetGroupBlock,
@@ -59,6 +60,8 @@ export function initialize( editorName, blockEditorSettings ) {
 			block.name.startsWith( 'core/navigation' )
 		);
 	} );
+
+	registerInternalWidgetIds();
 	registerCoreBlocks( coreBlocks );
 	registerLegacyWidgetBlock();
 	if ( process.env.IS_GUTENBERG_PLUGIN ) {
diff --git a/packages/edit-widgets/src/index.js b/packages/edit-widgets/src/index.js
index 5495ed11dff9d..0e8b9bf13eae6 100644
--- a/packages/edit-widgets/src/index.js
+++ b/packages/edit-widgets/src/index.js
@@ -16,6 +16,7 @@ import {
 } from '@wordpress/block-library';
 import { __experimentalFetchLinkSuggestions as fetchLinkSuggestions } from '@wordpress/core-data';
 import {
+	registerInternalWidgetIds,
 	registerLegacyWidgetBlock,
 	registerLegacyWidgetVariations,
 	registerWidgetGroupBlock,
@@ -85,7 +86,10 @@ export function initialize( id, settings ) {
 		themeStyles: true,
 	} );
 
+	registerInternalWidgetIds();
+
 	dispatch( blocksStore ).__experimentalReapplyBlockTypeFilters();
+
 	registerCoreBlocks( coreBlocks );
 	registerLegacyWidgetBlock();
 	if ( process.env.IS_GUTENBERG_PLUGIN ) {
diff --git a/packages/server-side-render/package.json b/packages/server-side-render/package.json
index 5c9390431f6b0..065a2d58eb292 100644
--- a/packages/server-side-render/package.json
+++ b/packages/server-side-render/package.json
@@ -28,7 +28,6 @@
 	"dependencies": {
 		"@babel/runtime": "^7.16.0",
 		"@wordpress/api-fetch": "file:../api-fetch",
-		"@wordpress/blocks": "file:../blocks",
 		"@wordpress/components": "file:../components",
 		"@wordpress/compose": "file:../compose",
 		"@wordpress/data": "file:../data",
diff --git a/packages/server-side-render/src/server-side-render.js b/packages/server-side-render/src/server-side-render.js
index 35338196f6c2b..7fa5426d4d888 100644
--- a/packages/server-side-render/src/server-side-render.js
+++ b/packages/server-side-render/src/server-side-render.js
@@ -12,7 +12,6 @@ import { __, sprintf } from '@wordpress/i18n';
 import apiFetch from '@wordpress/api-fetch';
 import { addQueryArgs } from '@wordpress/url';
 import { Placeholder, Spinner } from '@wordpress/components';
-import { __experimentalSanitizeBlockAttributes } from '@wordpress/blocks';
 
 export function rendererPath( block, attributes = null, urlQueryArgs = {} ) {
 	return addQueryArgs( `/wp/v2/block-renderer/${ block }`, {
@@ -88,20 +87,12 @@ export default function ServerSideRender( props ) {
 
 		setIsLoading( true );
 
-		const sanitizedAttributes =
-			attributes &&
-			__experimentalSanitizeBlockAttributes( block, attributes );
-
 		// If httpMethod is 'POST', send the attributes in the request body instead of the URL.
 		// This allows sending a larger attributes object than in a GET request, where the attributes are in the URL.
 		const isPostRequest = 'POST' === httpMethod;
-		const urlAttributes = isPostRequest
-			? null
-			: sanitizedAttributes ?? null;
+		const urlAttributes = isPostRequest ? null : attributes ?? null;
 		const path = rendererPath( block, urlAttributes, urlQueryArgs );
-		const data = isPostRequest
-			? { attributes: sanitizedAttributes ?? null }
-			: null;
+		const data = isPostRequest ? { attributes: attributes ?? null } : null;
 
 		// Store the latest fetch request so that when we process it, we can
 		// check if it is the current request, to avoid race conditions on slow networks.
diff --git a/packages/widgets/package.json b/packages/widgets/package.json
index e66199099fcae..1b866d8e8295a 100644
--- a/packages/widgets/package.json
+++ b/packages/widgets/package.json
@@ -29,6 +29,7 @@
 		"@wordpress/core-data": "file:../core-data",
 		"@wordpress/data": "file:../data",
 		"@wordpress/element": "file:../element",
+		"@wordpress/hooks": "file:../hooks",
 		"@wordpress/i18n": "file:../i18n",
 		"@wordpress/icons": "file:../icons",
 		"@wordpress/notices": "file:../notices",
diff --git a/packages/widgets/src/utils.js b/packages/widgets/src/utils.js
index 75b1f3d08140e..50b026ddd615a 100644
--- a/packages/widgets/src/utils.js
+++ b/packages/widgets/src/utils.js
@@ -1,4 +1,8 @@
 // @ts-check
+/**
+ * WordPress dependencies
+ */
+import { addFilter } from '@wordpress/hooks';
 
 /**
  * Get the internal widget id from block.
@@ -31,3 +35,32 @@ export function addWidgetIdToBlock( block, widgetId ) {
 		},
 	};
 }
+
+/**
+ * Filters registered block settings, extending attributes to include
+ * `__internalWidgetId` if needed.
+ *
+ * @param {Object} settings Original block settings.
+ *
+ * @return {Object} Updated block settings.
+ */
+function addInternalWidgetIdAttribute( settings ) {
+	return {
+		...settings,
+		attributes: {
+			...settings.attributes,
+			__internalWidgetId: {
+				type: 'string',
+				__experimentalRole: 'internal',
+			},
+		},
+	};
+}
+
+export function registerInternalWidgetIds() {
+	addFilter(
+		'blocks.registerBlockType',
+		'core/widget/addAttributes',
+		addInternalWidgetIdAttribute
+	);
+}