diff --git a/lib/compat/wordpress-6.3/rest-api.php b/lib/compat/wordpress-6.3/rest-api.php
index ecb8f52392fef9..d7fa31cd33fe6a 100644
--- a/lib/compat/wordpress-6.3/rest-api.php
+++ b/lib/compat/wordpress-6.3/rest-api.php
@@ -85,15 +85,18 @@ function add_modified_wp_template_schema() {
 }
 add_filter( 'rest_api_init', 'add_modified_wp_template_schema' );
 
-/**
- * Registers the block patterns REST API routes.
- */
-function gutenberg_register_rest_block_patterns() {
-	$block_patterns = new Gutenberg_REST_Block_Patterns_Controller_6_3();
-	$block_patterns->register_routes();
+// If the Auto-inserting Blocks experiment is enabled, we load the block patterns
+// controller in lib/experimental/rest-api.php instead.
+if ( ! gutenberg_is_experiment_enabled( 'gutenberg-auto-inserting-blocks' ) ) {
+	/**
+	 * Registers the block patterns REST API routes.
+	 */
+	function gutenberg_register_rest_block_patterns() {
+		$block_patterns = new Gutenberg_REST_Block_Patterns_Controller_6_3();
+		$block_patterns->register_routes();
+	}
+	add_action( 'rest_api_init', 'gutenberg_register_rest_block_patterns' );
 }
-add_action( 'rest_api_init', 'gutenberg_register_rest_block_patterns' );
-
 
 /**
  * Registers the Navigation Fallbacks REST API routes.
diff --git a/lib/experimental/auto-inserting-blocks.php b/lib/experimental/auto-inserting-blocks.php
new file mode 100644
index 00000000000000..9df94fcbfcd8fb
--- /dev/null
+++ b/lib/experimental/auto-inserting-blocks.php
@@ -0,0 +1,246 @@
+<?php
+/**
+ * Auto-inserting blocks.
+ *
+ * @package gutenberg
+ */
+
+/**
+ * Return a function that auto-inserts blocks relative to a given block.
+ *
+ * @param array  $inserted_block    The block to insert.
+ * @param string $relative_position The position relative to the given block.
+ * @param string $anchor_block      The block to insert relative to.
+ * @return callable A function that accepts a block's content and returns the content with the inserted block.
+ */
+function gutenberg_auto_insert_block( $inserted_block, $relative_position, $anchor_block ) {
+	return function( $block ) use ( $inserted_block, $relative_position, $anchor_block ) {
+		if ( $anchor_block === $block['blockName'] ) {
+			if ( 'first_child' === $relative_position ) {
+				array_unshift( $block['innerBlocks'], $inserted_block );
+				// Since WP_Block::render() iterates over `inner_content` (rather than `inner_blocks`)
+				// when rendering blocks, we also need to prepend a value (`null`, to mark a block
+				// location) to that array.
+				array_unshift( $block['innerContent'], null );
+			} elseif ( 'last_child' === $relative_position ) {
+				array_push( $block['innerBlocks'], $inserted_block );
+				// Since WP_Block::render() iterates over `inner_content` (rather than `inner_blocks`)
+				// when rendering blocks, we also need to prepend a value (`null`, to mark a block
+				// location) to that array.
+				array_push( $block['innerContent'], null );
+			}
+			return $block;
+		}
+
+		$anchor_block_index = array_search( $anchor_block, array_column( $block['innerBlocks'], 'blockName' ), true );
+		if ( false !== $anchor_block_index && ( 'after' === $relative_position || 'before' === $relative_position ) ) {
+			if ( 'after' === $relative_position ) {
+				$anchor_block_index++;
+			}
+			array_splice( $block['innerBlocks'], $anchor_block_index, 0, array( $inserted_block ) );
+
+			// Find matching `innerContent` chunk index.
+			$chunk_index = 0;
+			while ( $anchor_block_index > 0 ) {
+				if ( ! is_string( $block['innerContent'][ $chunk_index ] ) ) {
+					$anchor_block_index--;
+				}
+				$chunk_index++;
+			}
+			// Since WP_Block::render() iterates over `inner_content` (rather than `inner_blocks`)
+			// when rendering blocks, we also need to insert a value (`null`, to mark a block
+			// location) into that array.
+			array_splice( $block['innerContent'], $chunk_index, 0, array( null ) );
+		}
+		return $block;
+	};
+}
+
+/**
+ * Register blocks for auto-insertion, based on their block.json metadata.
+ *
+ * @param array $settings Array of determined settings for registering a block type.
+ * @param array $metadata Metadata provided for registering a block type.
+ * @return array Updated settings array.
+ */
+function gutenberg_register_auto_inserted_blocks( $settings, $metadata ) {
+	if ( ! isset( $metadata['__experimentalAutoInsert'] ) ) {
+		return $settings;
+	}
+	$auto_insert = $metadata['__experimentalAutoInsert'];
+
+	/**
+	 * Map the camelCased position string from block.json to the snake_cased block type position
+	 * used in the auto-inserting block registration function.
+	 *
+	 * @var array
+	 */
+	$property_mappings = array(
+		'before'     => 'before',
+		'after'      => 'after',
+		'firstChild' => 'first_child',
+		'lastChild'  => 'last_child',
+	);
+
+	$inserted_block_name = $metadata['name'];
+	foreach ( $auto_insert as $anchor_block_name => $position ) {
+		// Avoid infinite recursion (auto-inserting next to or into self).
+		if ( $inserted_block_name === $anchor_block_name ) {
+			_doing_it_wrong(
+				__METHOD__,
+				__( 'Cannot auto-insert block next to itself.', 'gutenberg' ),
+				'6.4.0'
+			);
+			continue;
+		}
+
+		if ( ! isset( $property_mappings[ $position ] ) ) {
+			continue;
+		}
+
+		$mapped_position = $property_mappings[ $position ];
+
+		gutenberg_register_auto_inserted_block( $inserted_block_name, $mapped_position, $anchor_block_name );
+
+		$settings['auto_insert'][ $anchor_block_name ] = $mapped_position;
+	}
+
+	return $settings;
+}
+add_filter( 'block_type_metadata_settings', 'gutenberg_register_auto_inserted_blocks', 10, 2 );
+
+/**
+ * Register block for auto-insertion into the frontend and REST API.
+ *
+ * Register a block for auto-insertion into the frontend and into the markup
+ * returned by the templates and patterns REST API endpoints.
+ *
+ * This is currently done by filtering parsed blocks as obtained from a block template
+ * template part, or pattern and injecting the auto-inserted block where applicable.
+ *
+ * @todo In the long run, we'd likely want some sort of registry for auto-inserted blocks.
+ *
+ * @param string $inserted_block  The name of the block to insert.
+ * @param string $position        The desired position of the auto-inserted block, relative to its anchor block.
+ *                                Can be 'before', 'after', 'first_child', or 'last_child'.
+ * @param string $anchor_block    The name of the block to insert the auto-inserted block next to.
+ * @return void
+ */
+function gutenberg_register_auto_inserted_block( $inserted_block, $position, $anchor_block ) {
+		$inserted_block = array(
+			'blockName'    => $inserted_block,
+			'attrs'        => array(),
+			'innerHTML'    => '',
+			'innerContent' => array(),
+			'innerBlocks'  => array(),
+		);
+
+		$inserter = gutenberg_auto_insert_block( $inserted_block, $position, $anchor_block );
+		add_filter( 'gutenberg_serialize_block', $inserter, 10, 1 );
+}
+
+/**
+ * Parse and reserialize block templates to allow running filters.
+ *
+ * By parsing a block template's content and then reserializing it
+ * via `gutenberg_serialize_blocks()`, we are able to run filters
+ * on the parsed blocks.
+ *
+ * @param WP_Block_Template[] $query_result Array of found block templates.
+ * @return WP_Block_Template[] Updated array of found block templates.
+ */
+function gutenberg_parse_and_serialize_block_templates( $query_result ) {
+	foreach ( $query_result as $block_template ) {
+		if ( 'custom' === $block_template->source ) {
+			continue;
+		}
+		$blocks                  = parse_blocks( $block_template->content );
+		$block_template->content = gutenberg_serialize_blocks( $blocks );
+	}
+
+	return $query_result;
+}
+add_filter( 'get_block_templates', 'gutenberg_parse_and_serialize_block_templates', 10, 1 );
+
+/**
+ * Filters the block template object after it has been (potentially) fetched from the theme file.
+ *
+ * By parsing a block template's content and then reserializing it
+ * via `gutenberg_serialize_blocks()`, we are able to run filters
+ * on the parsed blocks.
+ *
+ * @param WP_Block_Template|null $block_template The found block template, or null if there is none.
+ */
+function gutenberg_parse_and_serialize_blocks( $block_template ) {
+
+	$blocks                  = parse_blocks( $block_template->content );
+	$block_template->content = gutenberg_serialize_blocks( $blocks );
+
+	return $block_template;
+}
+add_filter( 'get_block_file_template', 'gutenberg_parse_and_serialize_blocks', 10, 1 );
+
+// Helper functions.
+// -----------------
+// The sole purpose of the following two functions (`gutenberg_serialize_block`
+// and `gutenberg_serialize_blocks`), which are otherwise copies of their unprefixed
+// counterparts (`serialize_block` and `serialize_blocks`) is to apply a filter
+// (also called `gutenberg_serialize_block`) as an entry point for modifications
+// to the parsed blocks.
+
+/**
+ * Filterable version of `serialize_block()`.
+ *
+ * This function is identical to `serialize_block()`, except that it applies
+ * the `gutenberg_serialize_block` filter to each block before it is serialized.
+ *
+ * @param array $block The block to be serialized.
+ * @return string The serialized block.
+ *
+ * @see serialize_block()
+ */
+function gutenberg_serialize_block( $block ) {
+	$block_content = '';
+
+	/**
+	 * Filters a parsed block before it is serialized.
+	 *
+	 * @param array $block The block to be serialized.
+	 */
+	$block = apply_filters( 'gutenberg_serialize_block', $block );
+
+	$index = 0;
+	foreach ( $block['innerContent'] as $chunk ) {
+		if ( is_string( $chunk ) ) {
+			$block_content .= $chunk;
+		} else { // Compare to WP_Block::render().
+			$inner_block    = $block['innerBlocks'][ $index++ ];
+			$block_content .= gutenberg_serialize_block( $inner_block );
+		}
+	}
+
+	if ( ! is_array( $block['attrs'] ) ) {
+		$block['attrs'] = array();
+	}
+
+	return get_comment_delimited_block_content(
+		$block['blockName'],
+		$block['attrs'],
+		$block_content
+	);
+}
+
+/**
+ * Filterable version of `serialize_blocks()`.
+ *
+ * This function is identical to `serialize_blocks()`, except that it applies
+ * the `gutenberg_serialize_block` filter to each block before it is serialized.
+ *
+ * @param array $blocks The blocks to be serialized.
+ * @return string[] The serialized blocks.
+ *
+ * @see serialize_blocks()
+ */
+function gutenberg_serialize_blocks( $blocks ) {
+	return implode( '', array_map( 'gutenberg_serialize_block', $blocks ) );
+}
diff --git a/lib/experimental/class-gutenberg-rest-block-patterns-controller.php b/lib/experimental/class-gutenberg-rest-block-patterns-controller.php
new file mode 100644
index 00000000000000..1ac567959b146f
--- /dev/null
+++ b/lib/experimental/class-gutenberg-rest-block-patterns-controller.php
@@ -0,0 +1,40 @@
+<?php
+/**
+ * REST API: Gutenberg_REST_Block_Patterns_Controller class
+ *
+ * @package    Gutenberg
+ * @subpackage REST_API
+ */
+
+/**
+ * Core class used to access block patterns via the REST API.
+ *
+ * @since 6.4.0
+ *
+ * @see WP_REST_Controller
+ */
+class Gutenberg_REST_Block_Patterns_Controller extends Gutenberg_REST_Block_Patterns_Controller_6_3 {
+	/**
+	 * Prepare a raw block pattern before it gets output in a REST API response.
+	 *
+	 * @todo In the long run, we'd likely want to have a filter in the `WP_Block_Patterns_Registry` class
+	 * instead to allow us plugging in code like this.
+	 *
+	 * @param array           $item    Raw pattern as registered, before any changes.
+	 * @param WP_REST_Request $request Request object.
+	 * @return WP_REST_Response|WP_Error Response object on success, or WP_Error object on failure.
+	 */
+	public function prepare_item_for_response( $item, $request ) {
+		$response = parent::prepare_item_for_response( $item, $request );
+		if ( ! gutenberg_is_experiment_enabled( 'gutenberg-auto-inserting-blocks' ) ) {
+			return $response;
+		}
+
+		$data = $response->get_data();
+
+		$blocks          = parse_blocks( $data['content'] );
+		$data['content'] = gutenberg_serialize_blocks( $blocks ); // Serialize or render?
+
+		return rest_ensure_response( $data );
+	}
+}
diff --git a/lib/experimental/rest-api.php b/lib/experimental/rest-api.php
index 7c6a9bf74d7395..8e548600b3875e 100644
--- a/lib/experimental/rest-api.php
+++ b/lib/experimental/rest-api.php
@@ -10,6 +10,17 @@
 	die( 'Silence is golden.' );
 }
 
+if ( gutenberg_is_experiment_enabled( 'gutenberg-auto-inserting-blocks' ) ) {
+	/**
+	 * Registers the block patterns REST API routes.
+	 */
+	function gutenberg_register_rest_block_patterns() {
+		$block_patterns = new Gutenberg_REST_Block_Patterns_Controller();
+		$block_patterns->register_routes();
+	}
+	add_action( 'rest_api_init', 'gutenberg_register_rest_block_patterns' );
+}
+
 /**
  * Registers the customizer nonces REST API routes.
  */
diff --git a/lib/experiments-page.php b/lib/experiments-page.php
index ce30242d20f81d..3f468d0cbd12db 100644
--- a/lib/experiments-page.php
+++ b/lib/experiments-page.php
@@ -91,6 +91,18 @@ function gutenberg_initialize_experiments_settings() {
 		)
 	);
 
+	add_settings_field(
+		'gutenberg-auto-inserting-blocks',
+		__( 'Auto-inserting blocks', 'gutenberg' ),
+		'gutenberg_display_experiment_field',
+		'gutenberg-experiments',
+		'gutenberg_experiments_section',
+		array(
+			'label' => __( 'Test Auto-inserting blocks', 'gutenberg' ),
+			'id'    => 'gutenberg-auto-inserting-blocks',
+		)
+	);
+
 	register_setting(
 		'gutenberg-experiments',
 		'gutenberg-experiments'
diff --git a/lib/load.php b/lib/load.php
index 71be1068b7061b..85e9f9575e6e6f 100644
--- a/lib/load.php
+++ b/lib/load.php
@@ -69,6 +69,9 @@ function gutenberg_is_experiment_enabled( $name ) {
 		require_once __DIR__ . '/experimental/class-wp-rest-customizer-nonces.php';
 	}
 	require_once __DIR__ . '/experimental/class-gutenberg-rest-template-revision-count.php';
+	if ( gutenberg_is_experiment_enabled( 'gutenberg-auto-inserting-blocks' ) ) {
+		require_once __DIR__ . '/experimental/class-gutenberg-rest-block-patterns-controller.php';
+	}
 	require_once __DIR__ . '/experimental/rest-api.php';
 }
 
@@ -117,6 +120,9 @@ function gutenberg_is_experiment_enabled( $name ) {
 	require __DIR__ . '/experimental/disable-tinymce.php';
 }
 
+if ( gutenberg_is_experiment_enabled( 'gutenberg-auto-inserting-blocks' ) ) {
+	require __DIR__ . '/experimental/auto-inserting-blocks.php';
+}
 require __DIR__ . '/experimental/interactivity-api/class-wp-interactivity-store.php';
 require __DIR__ . '/experimental/interactivity-api/store.php';
 require __DIR__ . '/experimental/interactivity-api/scripts.php';
diff --git a/packages/block-library/src/pattern/index.php b/packages/block-library/src/pattern/index.php
index 6368bdb7b74875..bc42e891d9f1fd 100644
--- a/packages/block-library/src/pattern/index.php
+++ b/packages/block-library/src/pattern/index.php
@@ -41,7 +41,17 @@ function render_block_core_pattern( $attributes ) {
 	}
 
 	$pattern = $registry->get_registered( $slug );
-	return do_blocks( $pattern['content'] );
+	$content = $pattern['content'];
+
+	$gutenberg_experiments = get_option( 'gutenberg-experiments' );
+	if ( $gutenberg_experiments && ! empty( $gutenberg_experiments['gutenberg-auto-inserting-blocks'] ) ) {
+		// TODO: In the long run, we'd likely want to have a filter in the `WP_Block_Patterns_Registry` class
+		// instead to allow us plugging in code like this.
+		$blocks  = parse_blocks( $content );
+		$content = gutenberg_serialize_blocks( $blocks );
+	}
+
+	return do_blocks( $content );
 }
 
 add_action( 'init', 'register_block_core_pattern' );