diff --git a/lib/class-wp-rest-block-editor-settings-controller.php b/lib/class-wp-rest-block-editor-settings-controller.php
index 8207d1b6bacbc6..717e2e7e56270a 100644
--- a/lib/class-wp-rest-block-editor-settings-controller.php
+++ b/lib/class-wp-rest-block-editor-settings-controller.php
@@ -134,12 +134,6 @@ public function get_item_schema() {
 					'context'     => array( 'post-editor', 'site-editor', 'widgets-editor', 'mobile' ),
 				),
 
-				'__experimentalGlobalStylesUserEntityId' => array(
-					'description' => __( 'Global styles user entity ID.', 'gutenberg' ),
-					'type'        => 'integer',
-					'context'     => array( 'site-editor' ),
-				),
-
 				'__experimentalGlobalStylesBaseConfig'   => array(
 					'description' => __( 'Settings and styles consolidated from core and theme origins.', 'gutenberg' ),
 					'type'        => 'object',
diff --git a/lib/compat/wordpress-5.9/class-gutenberg-rest-global-styles-controller.php b/lib/compat/wordpress-5.9/class-gutenberg-rest-global-styles-controller.php
new file mode 100644
index 00000000000000..7405af5e384946
--- /dev/null
+++ b/lib/compat/wordpress-5.9/class-gutenberg-rest-global-styles-controller.php
@@ -0,0 +1,341 @@
+<?php
+/**
+ * REST API: Gutenberg_REST_Global_Styles_Controller class
+ *
+ * @package    Gutenberg
+ * @subpackage REST_API
+ */
+
+/**
+ * Base Global Styles REST API Controller.
+ */
+class Gutenberg_REST_Global_Styles_Controller extends WP_REST_Controller {
+	/**
+	 * Post type.
+	 *
+	 * @var string
+	 */
+	protected $post_type;
+
+	/**
+	 * Constructor.
+	 */
+	public function __construct() {
+		$this->namespace = 'wp/v2';
+		$this->rest_base = 'global-styles';
+	}
+
+	/**
+	 * Registers the controllers routes.
+	 *
+	 * @return void
+	 */
+	public function register_routes() {
+		// Lists/updates a single gloval style variation based on the given id.
+		register_rest_route(
+			$this->namespace,
+			'/' . $this->rest_base . '/(?P<id>[\/\w-]+)',
+			array(
+				array(
+					'methods'             => WP_REST_Server::READABLE,
+					'callback'            => array( $this, 'get_item' ),
+					'permission_callback' => array( $this, 'get_item_permissions_check' ),
+					'args'                => array(
+						'id' => array(
+							'description' => __( 'The id of a template', 'gutenberg' ),
+							'type'        => 'string',
+						),
+					),
+				),
+				array(
+					'methods'             => WP_REST_Server::EDITABLE,
+					'callback'            => array( $this, 'update_item' ),
+					'permission_callback' => array( $this, 'update_item_permissions_check' ),
+					'args'                => $this->get_endpoint_args_for_item_schema( WP_REST_Server::EDITABLE ),
+				),
+				'schema' => array( $this, 'get_public_item_schema' ),
+			)
+		);
+	}
+
+	/**
+	 * Checks if the user has permissions to make the request.
+	 *
+	 * @return true|WP_Error True if the request has read access, WP_Error object otherwise.
+	 */
+	protected function permissions_check() {
+		// Verify if the current user has edit_theme_options capability.
+		// This capability is required to edit/view/delete templates.
+		if ( ! current_user_can( 'edit_theme_options' ) ) {
+			return new WP_Error(
+				'rest_cannot_manage_global_styles',
+				__( 'Sorry, you are not allowed to access the global styles on this site.', 'gutenberg' ),
+				array(
+					'status' => rest_authorization_required_code(),
+				)
+			);
+		}
+
+		return true;
+	}
+
+	/**
+	 * Checks if a given request has access to read a single global styles config.
+	 *
+	 * @param WP_REST_Request $request Full details about the request.
+	 * @return true|WP_Error True if the request has read access for the item, WP_Error object otherwise.
+	 */
+	public function get_item_permissions_check( $request ) {
+		return $this->permissions_check( $request );
+	}
+
+	/**
+	 * Returns the given global styles config.
+	 *
+	 * @param WP_REST_Request $request The request instance.
+	 *
+	 * @return WP_REST_Response|WP_Error
+	 */
+	public function get_item( $request ) {
+		$post = get_post( $request['id'] );
+		if ( ! $post || 'wp_global_styles' !== $post->post_type ) {
+			return new WP_Error( 'rest_global_styles_not_found', __( 'No global styles config exist with that id.', 'gutenberg' ), array( 'status' => 404 ) );
+		}
+
+		return $this->prepare_item_for_response( $post, $request );
+	}
+
+	/**
+	 * Checks if a given request has access to write a single global styles config.
+	 *
+	 * @param WP_REST_Request $request Full details about the request.
+	 * @return true|WP_Error True if the request has write access for the item, WP_Error object otherwise.
+	 */
+	public function update_item_permissions_check( $request ) {
+		return $this->permissions_check( $request );
+	}
+
+	/**
+	 * Updates a single global style config.
+	 *
+	 * @param WP_REST_Request $request Full details about the request.
+	 * @return WP_REST_Response|WP_Error Response object on success, or WP_Error object on failure.
+	 */
+	public function update_item( $request ) {
+		$post = get_post( $request['id'] );
+		if ( ! $post || 'wp_global_styles' !== $post->post_type ) {
+			return new WP_Error( 'rest_global_styles_not_found', __( 'No global styles config exist with that id.', 'gutenberg' ), array( 'status' => 404 ) );
+		}
+
+		$changes = $this->prepare_item_for_database( $request );
+		$result  = wp_update_post( wp_slash( (array) $changes ), true );
+		if ( is_wp_error( $result ) ) {
+			return $result;
+		}
+
+		$post          = get_post( $request['id'] );
+		$fields_update = $this->update_additional_fields_for_object( $post, $request );
+		if ( is_wp_error( $fields_update ) ) {
+			return $fields_update;
+		}
+
+		return $this->prepare_item_for_response(
+			get_post( $request['id'] ),
+			$request
+		);
+	}
+
+	/**
+	 * Prepares a single global styles config for update.
+	 *
+	 * @param WP_REST_Request $request Request object.
+	 * @return stdClass Changes to pass to wp_update_post.
+	 */
+	protected function prepare_item_for_database( $request ) {
+		$changes     = new stdClass();
+		$changes->ID = $request['id'];
+
+		$post         = get_post( $request['id'] );
+		$empty_config = array(
+			'settings' => new stdClass(),
+			'styles'   => new stdClass(),
+		);
+		if ( $post ) {
+			$existing_config = json_decode( $post->post_content, true );
+			if ( ! isset( $existing_config['isGlobalStylesUserThemeJSON'] ) ||
+				! $existing_config['isGlobalStylesUserThemeJSON'] ) {
+				$existing_config = $empty_config;
+			}
+		} else {
+			$existing_config = $empty_config;
+		}
+
+		if ( isset( $request['styles'] ) || isset( $request['settings'] ) ) {
+			$config = array();
+			if ( isset( $request['styles'] ) ) {
+				$config['styles'] = $request['styles'];
+			} else {
+				$config['styles'] = $existing_config['styles'];
+			}
+			if ( isset( $request['settings'] ) ) {
+				$config['settings'] = $request['settings'];
+			} else {
+				$config['settings'] = $existing_config['settings'];
+			}
+			$config['isGlobalStylesUserThemeJSON'] = true;
+			$config['version']                     = WP_Theme_JSON_Gutenberg::LATEST_SCHEMA;
+			$changes->post_content                 = wp_json_encode( $config );
+		}
+
+		// Post title.
+		if ( isset( $request['title'] ) ) {
+			if ( is_string( $request['title'] ) ) {
+				$changes->post_title = $request['title'];
+			} elseif ( ! empty( $request['title']['raw'] ) ) {
+				$changes->post_title = $request['title']['raw'];
+			}
+		}
+
+		return $changes;
+	}
+
+	/**
+	 * Prepare a global styles config output for response.
+	 *
+	 * @param WP_Post         $post    Global Styles post object.
+	 * @param WP_REST_Request $request Request object.
+	 *
+	 * @return WP_REST_Response $data
+	 */
+	public function prepare_item_for_response( $post, $request ) { // phpcs:ignore VariableAnalysis.CodeAnalysis.VariableAnalysis.UnusedVariable
+		$config                           = json_decode( $post->post_content, true );
+		$is_global_styles_user_theme_json = isset( $config['isGlobalStylesUserThemeJSON'] ) && true === $config['isGlobalStylesUserThemeJSON'];
+		$result                           = array(
+			'id'       => $post->ID,
+			'settings' => ! empty( $config['settings'] ) && $is_global_styles_user_theme_json ? $config['settings'] : new stdClass(),
+			'styles'   => ! empty( $config['styles'] ) && $is_global_styles_user_theme_json ? $config['styles'] : new stdClass(),
+			'title'    => array(
+				'raw'      => $post->post_title,
+				'rendered' => get_the_title( $post ),
+			),
+		);
+		$result                           = $this->add_additional_fields_to_object( $result, $request );
+		$response                         = rest_ensure_response( $result );
+		$links                            = $this->prepare_links( $post->id );
+		$response->add_links( $links );
+		if ( ! empty( $links['self']['href'] ) ) {
+			$actions = $this->get_available_actions();
+			$self    = $links['self']['href'];
+			foreach ( $actions as $rel ) {
+				$response->add_link( $rel, $self );
+			}
+		}
+
+		return $response;
+	}
+
+
+	/**
+	 * Prepares links for the request.
+	 *
+	 * @param integer $id ID.
+	 * @return array Links for the given post.
+	 */
+	protected function prepare_links( $id ) {
+		$base = sprintf( '%s/%s', $this->namespace, $this->rest_base );
+
+		$links = array(
+			'self'       => array(
+				'href' => rest_url( trailingslashit( $base ) . $id ),
+			),
+			'collection' => array(
+				'href' => rest_url( $base ),
+			),
+		);
+
+		return $links;
+	}
+
+	/**
+	 * Get the link relations available for the post and current user.
+	 *
+	 * @return array List of link relations.
+	 */
+	protected function get_available_actions() {
+		$rels = array();
+
+		$post_type = get_post_type_object( 'wp_global_styles' );
+		if ( current_user_can( $post_type->cap->publish_posts ) ) {
+			$rels[] = 'https://api.w.org/action-publish';
+		}
+
+		return $rels;
+	}
+
+	/**
+	 * Retrieves the query params for the global styles collection.
+	 *
+	 * @return array Collection parameters.
+	 */
+	public function get_collection_params() {
+		return array();
+	}
+
+	/**
+	 * Retrieves the global styles type' schema, conforming to JSON Schema.
+	 *
+	 * @return array Item schema data.
+	 */
+	public function get_item_schema() {
+		if ( $this->schema ) {
+			return $this->add_additional_fields_schema( $this->schema );
+		}
+
+		$schema = array(
+			'$schema'    => 'http://json-schema.org/draft-04/schema#',
+			'title'      => 'wp_global_styles',
+			'type'       => 'object',
+			'properties' => array(
+				'id'       => array(
+					'description' => __( 'ID of global styles config.', 'gutenberg' ),
+					'type'        => 'string',
+					'context'     => array( 'embed', 'view', 'edit' ),
+					'readonly'    => true,
+				),
+				'styles'   => array(
+					'description' => __( 'Global styles.', 'gutenberg' ),
+					'type'        => array( 'object' ),
+					'context'     => array( 'view', 'edit' ),
+				),
+				'settings' => array(
+					'description' => __( 'Global settings.', 'gutenberg' ),
+					'type'        => array( 'object' ),
+					'context'     => array( 'view', 'edit' ),
+				),
+				'title'    => array(
+					'description' => __( 'Title of the global styles variation.', 'gutenberg' ),
+					'type'        => array( 'object', 'string' ),
+					'default'     => '',
+					'context'     => array( 'embed', 'view', 'edit' ),
+					'properties'  => array(
+						'raw'      => array(
+							'description' => __( 'Title for the global styles variation, as it exists in the database.', 'gutenberg' ),
+							'type'        => 'string',
+							'context'     => array( 'view', 'edit', 'embed' ),
+						),
+						'rendered' => array(
+							'description' => __( 'HTML title for the post, transformed for display.', 'gutenberg' ),
+							'type'        => 'string',
+							'context'     => array( 'view', 'edit', 'embed' ),
+							'readonly'    => true,
+						),
+					),
+				),
+			),
+		);
+
+		$this->schema = $schema;
+
+		return $this->add_additional_fields_schema( $this->schema );
+	}
+}
diff --git a/lib/compat/wordpress-5.9/rest-active-global-styles.php b/lib/compat/wordpress-5.9/rest-active-global-styles.php
new file mode 100644
index 00000000000000..b0aa325f8cf483
--- /dev/null
+++ b/lib/compat/wordpress-5.9/rest-active-global-styles.php
@@ -0,0 +1,47 @@
+<?php
+/**
+ * Extends the themes endpoint to add the global styles link.
+ *
+ * @package gutenberg
+ */
+
+/**
+ * Adds the current global styles link to the theme's REST API response.
+ *
+ * @param WP_REST_Response $response The response object.
+ * @param WP_Theme         $theme    The theme object.
+ */
+function gutenberg_add_active_global_styles_link( $response, $theme ) {
+	if ( $theme->get_stylesheet() === wp_get_theme()->get_stylesheet() ) {
+		// This creates a record for the current theme if not existant.
+		$id = WP_Theme_JSON_Resolver_Gutenberg::get_user_custom_post_type_id();
+	} else {
+
+		$wp_query_args       = array(
+			'post_status'    => array( 'publish' ),
+			'post_type'      => 'wp_global_styles',
+			'posts_per_page' => 1,
+			'no_found_rows'  => true,
+			'tax_query'      => array(
+				array(
+					'taxonomy' => 'wp_theme',
+					'field'    => 'name',
+					'terms'    => $theme->get_stylesheet(),
+				),
+			),
+		);
+		$global_styles_query = new WP_Query( $wp_query_args );
+		$id                  = count( $global_styles_query->posts ) ? $global_styles_query->posts[0]->ID : null;
+	}
+
+	if ( $id ) {
+		$response->add_link(
+			'https://api.w.org/user-global-styles',
+			rest_url( 'wp/v2/global-styles/' . $id )
+		);
+	}
+
+	return $response;
+}
+
+add_filter( 'rest_prepare_theme', 'gutenberg_add_active_global_styles_link', 10, 2 );
diff --git a/lib/global-styles.php b/lib/global-styles.php
index e33f79bb758b8a..acbd8c1123d9d2 100644
--- a/lib/global-styles.php
+++ b/lib/global-styles.php
@@ -122,10 +122,8 @@ function_exists( 'gutenberg_is_edit_site_page' ) &&
 	}
 
 	if ( 'site-editor' === $context && gutenberg_experimental_is_site_editor_available() ) {
-		$theme       = WP_Theme_JSON_Resolver_Gutenberg::get_merged_data( $settings, 'theme' );
-		$user_cpt_id = WP_Theme_JSON_Resolver_Gutenberg::get_user_custom_post_type_id();
+		$theme = WP_Theme_JSON_Resolver_Gutenberg::get_merged_data( $settings, 'theme' );
 
-		$settings['__experimentalGlobalStylesUserEntityId']           = $user_cpt_id;
 		$settings['__experimentalGlobalStylesBaseConfig']['styles']   = $theme->get_raw_data()['styles'];
 		$settings['__experimentalGlobalStylesBaseConfig']['settings'] = $theme->get_settings();
 	}
diff --git a/lib/load.php b/lib/load.php
index 14dac73e96e6f3..511ac6f1568f79 100644
--- a/lib/load.php
+++ b/lib/load.php
@@ -109,6 +109,8 @@ function gutenberg_is_experiment_enabled( $name ) {
 require __DIR__ . '/full-site-editing/edit-site-page.php';
 require __DIR__ . '/full-site-editing/edit-site-export.php';
 require __DIR__ . '/compat/wordpress-5.9/default-theme-supports.php';
+require __DIR__ . '/compat/wordpress-5.9/class-gutenberg-rest-global-styles-controller.php';
+require __DIR__ . '/compat/wordpress-5.9/rest-active-global-styles.php';
 
 require __DIR__ . '/blocks.php';
 require __DIR__ . '/block-patterns.php';
diff --git a/lib/rest-api.php b/lib/rest-api.php
index aa74c373f8b5b1..4829b6367711d8 100644
--- a/lib/rest-api.php
+++ b/lib/rest-api.php
@@ -224,3 +224,12 @@ function gutenberg_rest_user_collection_params_has_published_posts( $query_param
 	return $query_params;
 }
 add_filter( 'rest_user_collection_params', 'gutenberg_rest_user_collection_params_has_published_posts' );
+
+/**
+ * Registers the Global Styles REST API routes.
+ */
+function gutenberg_register_global_styles_endpoints() {
+	$editor_settings = new Gutenberg_REST_Global_Styles_Controller();
+	$editor_settings->register_routes();
+}
+add_action( 'rest_api_init', 'gutenberg_register_global_styles_endpoints' );
diff --git a/packages/core-data/src/actions.js b/packages/core-data/src/actions.js
index ba70a25395a0f0..0b184f8fec4e7f 100644
--- a/packages/core-data/src/actions.js
+++ b/packages/core-data/src/actions.js
@@ -117,6 +117,22 @@ export function receiveCurrentTheme( currentTheme ) {
 	};
 }
 
+/**
+ * Returns an action object used in signalling that the current global styles id has been received.
+ *
+ * @param {string} currentGlobalStylesId The current global styles id.
+ *
+ * @return {Object} Action object.
+ */
+export function __experimentalReceiveCurrentGlobalStylesId(
+	currentGlobalStylesId
+) {
+	return {
+		type: 'RECEIVE_CURRENT_GLOBAL_STYLES_ID',
+		id: currentGlobalStylesId,
+	};
+}
+
 /**
  * Returns an action object used in signalling that the index has been received.
  *
diff --git a/packages/core-data/src/entities.js b/packages/core-data/src/entities.js
index 03fafbe099bcc4..4fd73ea2b86912 100644
--- a/packages/core-data/src/entities.js
+++ b/packages/core-data/src/entities.js
@@ -127,6 +127,15 @@ export const defaultEntities = [
 		label: __( 'Menu Location' ),
 		key: 'name',
 	},
+	{
+		label: __( 'Global Styles' ),
+		name: 'globalStyles',
+		kind: 'root',
+		baseURL: '/wp/v2/global-styles',
+		baseURLParams: { context: 'edit' },
+		plural: 'globalStylesVariations', // should be different than name
+		getTitle: ( record ) => record?.title?.rendered || record?.title,
+	},
 ];
 
 export const kinds = [
diff --git a/packages/core-data/src/reducer.js b/packages/core-data/src/reducer.js
index f78e6fd76eff9d..8404b59a5a59cd 100644
--- a/packages/core-data/src/reducer.js
+++ b/packages/core-data/src/reducer.js
@@ -119,6 +119,23 @@ export function currentTheme( state = undefined, action ) {
 	return state;
 }
 
+/**
+ * Reducer managing the current global styles id.
+ *
+ * @param {string} state  Current state.
+ * @param {Object} action Dispatched action.
+ *
+ * @return {string} Updated state.
+ */
+export function currentGlobalStylesId( state = undefined, action ) {
+	switch ( action.type ) {
+		case 'RECEIVE_CURRENT_GLOBAL_STYLES_ID':
+			return action.id;
+	}
+
+	return state;
+}
+
 /**
  * Reducer managing installed themes.
  *
@@ -570,6 +587,7 @@ export default combineReducers( {
 	terms,
 	users,
 	currentTheme,
+	currentGlobalStylesId,
 	currentUser,
 	taxonomies,
 	themes,
diff --git a/packages/core-data/src/resolvers.js b/packages/core-data/src/resolvers.js
index 7ff03976a8b4b0..1b66ae40751765 100644
--- a/packages/core-data/src/resolvers.js
+++ b/packages/core-data/src/resolvers.js
@@ -418,3 +418,26 @@ __experimentalGetTemplateForLink.shouldInvalidate = ( action ) => {
 		action.name === 'wp_template'
 	);
 };
+
+export const __experimentalGetCurrentGlobalStylesId = () => async ( {
+	dispatch,
+} ) => {
+	const activeThemes = await apiFetch( {
+		path: '/wp/v2/themes?status=active',
+	} );
+	const globalStylesURL = get( activeThemes, [
+		0,
+		'_links',
+		'wp:user-global-styles',
+		0,
+		'href',
+	] );
+	if ( globalStylesURL ) {
+		const globalStylesObject = await apiFetch( {
+			url: globalStylesURL,
+		} );
+		dispatch.__experimentalReceiveCurrentGlobalStylesId(
+			globalStylesObject.id
+		);
+	}
+};
diff --git a/packages/core-data/src/selectors.js b/packages/core-data/src/selectors.js
index c0c6de522a4fe7..46f3bf8043e899 100644
--- a/packages/core-data/src/selectors.js
+++ b/packages/core-data/src/selectors.js
@@ -687,6 +687,17 @@ export function getCurrentTheme( state ) {
 	return state.themes[ state.currentTheme ];
 }
 
+/**
+ * Return the ID of the current global styles object.
+ *
+ * @param {Object} state Data state.
+ *
+ * @return {string} The current global styles ID.
+ */
+export function __experimentalGetCurrentGlobalStylesId( state ) {
+	return state.currentGlobalStylesId;
+}
+
 /**
  * Return theme supports data in the index.
  *
diff --git a/packages/edit-site/src/components/global-styles/global-styles-provider.js b/packages/edit-site/src/components/global-styles/global-styles-provider.js
index f83e0804167e61..79b911067bf570 100644
--- a/packages/edit-site/src/components/global-styles/global-styles-provider.js
+++ b/packages/edit-site/src/components/global-styles/global-styles-provider.js
@@ -1,7 +1,17 @@
 /**
  * External dependencies
  */
-import { get, cloneDeep, set, mergeWith } from 'lodash';
+import {
+	get,
+	cloneDeep,
+	set,
+	mergeWith,
+	pickBy,
+	isEmpty,
+	isObject,
+	identity,
+	mapValues,
+} from 'lodash';
 
 /**
  * WordPress dependencies
@@ -53,69 +63,63 @@ function removeUserOriginFromSettings( settingsToRemove ) {
 	} );
 	return newSettings;
 }
+const cleanEmptyObject = ( object ) => {
+	if ( ! isObject( object ) || Array.isArray( object ) ) {
+		return object;
+	}
+	const cleanedNestedObjects = pickBy(
+		mapValues( object, cleanEmptyObject ),
+		identity
+	);
+	return isEmpty( cleanedNestedObjects ) ? undefined : cleanedNestedObjects;
+};
 
 function useGlobalStylesUserConfig() {
-	const { globalStylesId, content } = useSelect( ( select ) => {
-		const _globalStylesId = select( editSiteStore ).getSettings()
-			.__experimentalGlobalStylesUserEntityId;
+	const { globalStylesId, settings, styles } = useSelect( ( select ) => {
+		const _globalStylesId = select(
+			coreStore
+		).__experimentalGetCurrentGlobalStylesId();
+		const record = _globalStylesId
+			? select( coreStore ).getEditedEntityRecord(
+					'root',
+					'globalStyles',
+					_globalStylesId
+			  )
+			: undefined;
 		return {
 			globalStylesId: _globalStylesId,
-			content: select( coreStore ).getEditedEntityRecord(
-				'postType',
-				'wp_global_styles',
-				_globalStylesId
-			)?.content,
+			settings: record?.settings,
+			styles: record?.styles,
 		};
 	}, [] );
 	const { getEditedEntityRecord } = useSelect( coreStore );
 	const { editEntityRecord } = useDispatch( coreStore );
 
-	const parseContent = ( contentToParse ) => {
-		let parsedConfig;
-		try {
-			parsedConfig = contentToParse ? JSON.parse( contentToParse ) : {};
-			// It is very important to verify if the flag isGlobalStylesUserThemeJSON is true.
-			// If it is not true the content was not escaped and is not safe.
-			if ( ! parsedConfig.isGlobalStylesUserThemeJSON ) {
-				parsedConfig = {};
-			} else {
-				parsedConfig = {
-					...parsedConfig,
-					settings: addUserOriginToSettings( parsedConfig.settings ),
-				};
-			}
-		} catch ( e ) {
-			/* eslint-disable no-console */
-			console.error( 'Global Styles User data is not valid' );
-			console.error( e );
-			/* eslint-enable no-console */
-			parsedConfig = {};
-		}
-
-		return parsedConfig;
-	};
-
 	const config = useMemo( () => {
-		return parseContent( content );
-	}, [ content ] );
+		return {
+			settings: addUserOriginToSettings( settings ?? {} ),
+			styles: styles ?? {},
+		};
+	}, [ settings, styles ] );
 
 	const setConfig = useCallback(
 		( callback ) => {
-			const currentConfig = parseContent(
-				getEditedEntityRecord(
-					'postType',
-					'wp_global_styles',
-					globalStylesId
-				)?.content
+			const record = getEditedEntityRecord(
+				'root',
+				'globalStyles',
+				globalStylesId
 			);
+			const currentConfig = {
+				styles: record?.styles ?? {},
+				settings: addUserOriginToSettings( record?.settings ?? {} ),
+			};
 			const updatedConfig = callback( currentConfig );
-			editEntityRecord( 'postType', 'wp_global_styles', globalStylesId, {
-				content: JSON.stringify( {
-					...updatedConfig,
-					settings: removeUserOriginFromSettings(
-						updatedConfig.settings
-					),
-				} ),
+			editEntityRecord( 'root', 'globalStyles', globalStylesId, {
+				styles: cleanEmptyObject( updatedConfig.styles ) || {},
+				settings:
+					cleanEmptyObject(
+						removeUserOriginFromSettings( updatedConfig.settings )
+					) || {},
 			} );
 		},
 		[ globalStylesId ]
diff --git a/packages/editor/src/components/provider/use-block-editor-settings.js b/packages/editor/src/components/provider/use-block-editor-settings.js
index 03cd44e35f2af6..c9235140c01f13 100644
--- a/packages/editor/src/components/provider/use-block-editor-settings.js
+++ b/packages/editor/src/components/provider/use-block-editor-settings.js
@@ -95,7 +95,6 @@ function useBlockEditorSettings( settings, hasTemplate ) {
 				'__experimentalBlockPatterns',
 				'__experimentalFeatures',
 				'__experimentalGlobalStylesBaseConfig',
-				'__experimentalGlobalStylesUserEntityId',
 				'__experimentalPreferredStyleVariations',
 				'__experimentalSetIsInserterOpened',
 				'__unstableGalleryWithImageBlocks',
diff --git a/phpunit/class-gutenberg-rest-global-styles-controller-test.php b/phpunit/class-gutenberg-rest-global-styles-controller-test.php
new file mode 100644
index 00000000000000..e933bfbba98e07
--- /dev/null
+++ b/phpunit/class-gutenberg-rest-global-styles-controller-test.php
@@ -0,0 +1,119 @@
+<?php
+
+class Gutenberg_REST_Global_Styles_Controller_Test extends WP_Test_REST_Controller_Testcase {
+	/**
+	 * @var int
+	 */
+	protected static $admin_id;
+
+	/**
+	 * @var int
+	 */
+	protected static $global_styles_id;
+
+	private function find_and_normalize_global_styles_by_id( $global_styles, $id ) {
+		foreach ( $global_styles as $style ) {
+			if ( $style['id'] === $id ) {
+				unset( $style['_links'] );
+				return $style;
+			}
+		}
+
+		return null;
+	}
+
+	/**
+	 * Create fake data before our tests run.
+	 *
+	 * @param WP_UnitTest_Factory $factory Helper that lets us create fake data.
+	 */
+	public static function wpSetupBeforeClass( $factory ) {
+		switch_theme( 'tt1-blocks' );
+		gutenberg_register_wp_theme_taxonomy();
+		self::$admin_id = $factory->user->create(
+			array(
+				'role' => 'administrator',
+			)
+		);
+		// This creates the global styles for the current theme.
+		self::$global_styles_id = wp_insert_post(
+			array(
+				'post_content' => '{"version": ' . WP_Theme_JSON_Gutenberg::LATEST_SCHEMA . ', "isGlobalStylesUserThemeJSON": true }',
+				'post_status'  => 'publish',
+				'post_title'   => __( 'Custom Styles', 'default' ),
+				'post_type'    => 'wp_global_styles',
+				'post_name'    => 'wp-global-styles-tt1-blocks',
+				'tax_input'    => array(
+					'wp_theme' => 'tt1-blocks',
+				),
+			),
+			true
+		);
+	}
+
+	public function test_register_routes() {
+		$routes = rest_get_server()->get_routes();
+		$this->assertArrayHasKey( '/wp/v2/global-styles/(?P<id>[\/\w-]+)', $routes );
+	}
+
+	public function test_context_param() {
+		// TODO: Implement test_context_param() method.
+		$this->markTestIncomplete();
+	}
+
+	public function test_get_items() {
+		$this->markTestIncomplete();
+	}
+
+	public function test_get_item() {
+		wp_set_current_user( self::$admin_id );
+		$request  = new WP_REST_Request( 'GET', '/wp/v2/global-styles/' . self::$global_styles_id );
+		$response = rest_get_server()->dispatch( $request );
+		$data     = $response->get_data();
+		unset( $data['_links'] );
+
+		$this->assertEquals(
+			array(
+				'id'       => self::$global_styles_id,
+				'title'    => array(
+					'raw'      => 'Custom Styles',
+					'rendered' => 'Custom Styles',
+				),
+				'settings' => new stdClass(),
+				'styles'   => new stdClass(),
+			),
+			$data
+		);
+	}
+
+	public function test_create_item() {
+		$this->markTestIncomplete();
+	}
+
+	public function test_update_item() {
+		wp_set_current_user( self::$admin_id );
+		$request = new WP_REST_Request( 'PUT', '/wp/v2/global-styles/' . self::$global_styles_id );
+		$request->set_body_params(
+			array(
+				'title' => 'My new global styles title',
+			)
+		);
+		$response = rest_get_server()->dispatch( $request );
+		$data     = $response->get_data();
+		$this->assertEquals( 'My new global styles title', $data['title']['raw'] );
+	}
+
+	public function test_delete_item() {
+		$this->markTestIncomplete();
+	}
+
+	public function test_prepare_item() {
+		// TODO: Implement test_prepare_item() method.
+		$this->markTestIncomplete();
+	}
+
+	public function test_get_item_schema() {
+		// TODO: Implement test_get_item_schema() method.
+		$this->markTestIncomplete();
+	}
+}