diff --git a/wp-includes/class-wp-theme-json-data.php b/wp-includes/class-wp-theme-json-data.php
new file mode 100644
index 0000000000..089e65eddb
--- /dev/null
+++ b/wp-includes/class-wp-theme-json-data.php
@@ -0,0 +1,72 @@
+<?php
+/**
+ * WP_Theme_JSON_Data class
+ *
+ * @package WordPress
+ * @subpackage Theme
+ * @since 6.1.0
+ */
+
+/**
+ * Class to provide access to update a theme.json structure.
+ */
+class WP_Theme_JSON_Data {
+
+	/**
+	 * Container of the data to update.
+	 *
+	 * @since 6.1.0
+	 * @var WP_Theme_JSON
+	 */
+	private $theme_json = null;
+
+	/**
+	 * The origin of the data: default, theme, user, etc.
+	 *
+	 * @since 6.1.0
+	 * @var string
+	 */
+	private $origin = '';
+
+	/**
+	 * Constructor.
+	 *
+	 * @since 6.1.0
+	 *
+	 * @link https://developer.wordpress.org/block-editor/reference-guides/theme-json-reference/
+	 *
+	 * @param array  $data   Array following the theme.json specification.
+	 * @param string $origin The origin of the data: default, theme, user.
+	 */
+	public function __construct( $data = array(), $origin = 'theme' ) {
+		$this->origin     = $origin;
+		$this->theme_json = new WP_Theme_JSON( $data, $this->origin );
+	}
+
+	/**
+	 * Updates the theme.json with the the given data.
+	 *
+	 * @since 6.1.0
+	 *
+	 * @param array $new_data Array following the theme.json specification.
+	 *
+	 * @return WP_Theme_JSON_Data The own instance with access to the modified data.
+	 */
+	public function update_with( $new_data ) {
+		$this->theme_json->merge( new WP_Theme_JSON( $new_data, $this->origin ) );
+		return $this;
+	}
+
+	/**
+	 * Returns an array containing the underlying data
+	 * following the theme.json specification.
+	 *
+	 * @since 6.1.0
+	 *
+	 * @return array
+	 */
+	public function get_data() {
+		return $this->theme_json->get_raw_data();
+	}
+
+}
diff --git a/wp-includes/class-wp-theme-json-resolver.php b/wp-includes/class-wp-theme-json-resolver.php
index 1efb8a4c8a..4acc61a784 100644
--- a/wp-includes/class-wp-theme-json-resolver.php
+++ b/wp-includes/class-wp-theme-json-resolver.php
@@ -137,6 +137,15 @@ public static function get_core_data() {
 
 		$config       = static::read_json_file( __DIR__ . '/theme.json' );
 		$config       = static::translate( $config );
+		/**
+		 * Filters the default data provided by WordPress for global styles & settings.
+		 *
+		 * @since 6.1.0
+		 *
+		 * @param WP_Theme_JSON_Data Class to access and update the underlying data.
+		 */
+		$theme_json   = apply_filters( 'theme_json_default', new WP_Theme_JSON_Data( $config, 'default' ) );
+		$config       = $theme_json->get_data();
 		static::$core = new WP_Theme_JSON( $config, 'default' );
 
 		return static::$core;
@@ -172,6 +181,15 @@ public static function get_theme_data( $deprecated = array(), $options = array()
 		if ( null === static::$theme ) {
 			$theme_json_data = static::read_json_file( static::get_file_path_from_theme( 'theme.json' ) );
 			$theme_json_data = static::translate( $theme_json_data, wp_get_theme()->get( 'TextDomain' ) );
+			/**
+			 * Filters the data provided by the theme for global styles & settings.
+			 *
+			 * @since 6.1.0
+			 *
+			 * @param WP_Theme_JSON_Data Class to access and update the underlying data.
+			 */
+			$theme_json      = apply_filters( 'theme_json_theme', new WP_Theme_JSON_Data( $theme_json_data, 'theme' ) );
+			$theme_json_data = $theme_json->get_data();
 			static::$theme   = new WP_Theme_JSON( $theme_json_data );
 
 			if ( wp_get_theme()->parent() ) {
@@ -258,6 +276,16 @@ public static function get_block_data() {
 			}
 		}
 
+		/**
+		 * Filters the data provided by the blocks for global styles & settings.
+		 *
+		 * @since 6.1.0
+		 *
+		 * @param WP_Theme_JSON_Data Class to access and update the underlying data.
+		 */
+		$theme_json = apply_filters( 'theme_json_blocks', new WP_Theme_JSON_Data( $config, 'core' ) );
+		$config     = $theme_json->get_data();
+
 		// Core here means it's the lower level part of the styles chain.
 		// It can be a core or a third-party block.
 		return new WP_Theme_JSON( $config, 'core' );
@@ -382,6 +410,15 @@ public static function get_user_data() {
 			$json_decoding_error = json_last_error();
 			if ( JSON_ERROR_NONE !== $json_decoding_error ) {
 				trigger_error( 'Error when decoding a theme.json schema for user data. ' . json_last_error_msg() );
+				/**
+				 * Filters the data provided by the user for global styles & settings.
+				 *
+				 * @since 6.1.0
+				 *
+				 * @param WP_Theme_JSON_Data Class to access and update the underlying data.
+				 */
+				$theme_json = apply_filters( 'theme_json_user', new WP_Theme_JSON_Data( $config, 'custom' ) );
+				$config     = $theme_json->get_data();
 				return new WP_Theme_JSON( $config, 'custom' );
 			}
 
@@ -396,6 +433,16 @@ public static function get_user_data() {
 				$config = $decoded_data;
 			}
 		}
+
+		/**
+		 * Filters the data provided by the user for global styles & settings.
+		 *
+		 * @since 6.1.0
+		 *
+		 * @param WP_Theme_JSON_Data Class to access and update the underlying data.
+		 */
+		$theme_json   = apply_filters( 'theme_json_user', new WP_Theme_JSON_Data( $config, 'custom' ) );
+		$config       = $theme_json->get_data();
 		static::$user = new WP_Theme_JSON( $config, 'custom' );
 
 		return static::$user;
diff --git a/wp-includes/version.php b/wp-includes/version.php
index 8dd22fcd12..721da9b913 100644
--- a/wp-includes/version.php
+++ b/wp-includes/version.php
@@ -16,7 +16,7 @@
  *
  * @global string $wp_version
  */
-$wp_version = '6.1-alpha-54250';
+$wp_version = '6.1-alpha-54251';
 
 /**
  * Holds the WordPress DB revision, increments when changes are made to the WordPress DB schema.
diff --git a/wp-settings.php b/wp-settings.php
index 6f0e33bd7e..d80d79bb82 100644
--- a/wp-settings.php
+++ b/wp-settings.php
@@ -172,6 +172,7 @@
 require ABSPATH . WPINC . '/theme.php';
 require ABSPATH . WPINC . '/class-wp-theme.php';
 require ABSPATH . WPINC . '/class-wp-theme-json-schema.php';
+require ABSPATH . WPINC . '/class-wp-theme-json-data.php';
 require ABSPATH . WPINC . '/class-wp-theme-json.php';
 require ABSPATH . WPINC . '/class-wp-theme-json-resolver.php';
 require ABSPATH . WPINC . '/global-styles-and-settings.php';