diff --git a/src/wp-includes/class-wp-dependency.php b/src/wp-includes/class-wp-dependency.php
index 7e8de9c595335..6666b166af7ad 100644
--- a/src/wp-includes/class-wp-dependency.php
+++ b/src/wp-includes/class-wp-dependency.php
@@ -50,7 +50,7 @@ class _WP_Dependency {
 	 * Used for cache-busting.
 	 *
 	 * @since 2.6.0
-	 * @var bool|string
+	 * @var string|false|null
 	 */
 	public $ver = false;
 
diff --git a/src/wp-includes/class-wp-script-modules.php b/src/wp-includes/class-wp-script-modules.php
index 52537b1a3412e..07402f66b3f20 100644
--- a/src/wp-includes/class-wp-script-modules.php
+++ b/src/wp-includes/class-wp-script-modules.php
@@ -41,6 +41,15 @@ class WP_Script_Modules {
 	 */
 	private $a11y_available = false;
 
+	/**
+	 * Holds a mapping of dependents (as IDs) for a given script ID.
+	 * Used to optimize recursive dependency tree checks.
+	 *
+	 * @since 6.9.0
+	 * @var array<string, string[]>
+	 */
+	private $dependents_map = array();
+
 	/**
 	 * Registers the script module if no script module with that script module
 	 * identifier has already been registered.
@@ -269,6 +278,38 @@ public function add_hooks() {
 		add_action( 'admin_print_footer_scripts', array( $this, 'print_a11y_script_module_html' ), 20 );
 	}
 
+	/**
+	 * Gets the highest fetch priority for the provided script IDs.
+	 *
+	 * @since 6.9.0
+	 *
+	 * @param string[] $ids Script module IDs.
+	 * @return string Highest fetch priority for the provided script module IDs.
+	 */
+	private function get_highest_fetchpriority( array $ids ): string {
+		static $priorities   = array(
+			'low',
+			'auto',
+			'high',
+		);
+		$high_priority_index = count( $priorities ) - 1;
+
+		$highest_priority_index = 0;
+		foreach ( $ids as $id ) {
+			if ( isset( $this->registered[ $id ] ) ) {
+				$highest_priority_index = max(
+					$highest_priority_index,
+					array_search( $this->registered[ $id ]['fetchpriority'], $priorities, true )
+				);
+				if ( $high_priority_index === $highest_priority_index ) {
+					break;
+				}
+			}
+		}
+
+		return $priorities[ $highest_priority_index ];
+	}
+
 	/**
 	 * Prints the enqueued script modules using script tags with type="module"
 	 * attributes.
@@ -282,15 +323,21 @@ public function print_enqueued_script_modules() {
 				'src'  => $this->get_src( $id ),
 				'id'   => $id . '-js-module',
 			);
-			if ( 'auto' !== $script_module['fetchpriority'] ) {
-				$args['fetchpriority'] = $script_module['fetchpriority'];
+
+			$dependents    = $this->get_recursive_dependents( $id );
+			$fetchpriority = $this->get_highest_fetchpriority( array_merge( array( $id ), $dependents ) );
+			if ( 'auto' !== $fetchpriority ) {
+				$args['fetchpriority'] = $fetchpriority;
+			}
+			if ( $fetchpriority !== $script_module['fetchpriority'] ) {
+				$args['data-wp-fetchpriority'] = $script_module['fetchpriority'];
 			}
 			wp_print_script_tag( $args );
 		}
 	}
 
 	/**
-	 * Prints the the static dependencies of the enqueued script modules using
+	 * Prints the static dependencies of the enqueued script modules using
 	 * link tags with rel="modulepreload" attributes.
 	 *
 	 * If a script module is marked for enqueue, it will not be preloaded.
@@ -301,12 +348,20 @@ public function print_script_module_preloads() {
 		foreach ( $this->get_dependencies( array_unique( $this->queue ), array( 'static' ) ) as $id => $script_module ) {
 			// Don't preload if it's marked for enqueue.
 			if ( ! in_array( $id, $this->queue, true ) ) {
-				echo sprintf(
-					'<link rel="modulepreload" href="%s" id="%s"%s>',
+				$enqueued_dependents   = array_intersect( $this->get_recursive_dependents( $id ), $this->queue );
+				$highest_fetchpriority = $this->get_highest_fetchpriority( $enqueued_dependents );
+				printf(
+					'<link rel="modulepreload" href="%s" id="%s"',
 					esc_url( $this->get_src( $id ) ),
-					esc_attr( $id . '-js-modulepreload' ),
-					'auto' !== $script_module['fetchpriority'] ? sprintf( ' fetchpriority="%s"', esc_attr( $script_module['fetchpriority'] ) ) : ''
+					esc_attr( $id . '-js-modulepreload' )
 				);
+				if ( 'auto' !== $highest_fetchpriority ) {
+					printf( ' fetchpriority="%s"', esc_attr( $highest_fetchpriority ) );
+				}
+				if ( $highest_fetchpriority !== $script_module['fetchpriority'] && 'auto' !== $script_module['fetchpriority'] ) {
+					printf( ' data-wp-fetchpriority="%s"', esc_attr( $script_module['fetchpriority'] ) );
+				}
+				echo ">\n";
 			}
 		}
 	}
@@ -374,18 +429,20 @@ private function get_marked_for_enqueue(): array {
 	 *                               Default is both.
 	 * @return array[] List of dependencies, keyed by script module identifier.
 	 */
-	private function get_dependencies( array $ids, array $import_types = array( 'static', 'dynamic' ) ) {
+	private function get_dependencies( array $ids, array $import_types = array( 'static', 'dynamic' ) ): array {
 		return array_reduce(
 			$ids,
 			function ( $dependency_script_modules, $id ) use ( $import_types ) {
 				$dependencies = array();
-				foreach ( $this->registered[ $id ]['dependencies'] as $dependency ) {
-					if (
-					in_array( $dependency['import'], $import_types, true ) &&
-					isset( $this->registered[ $dependency['id'] ] ) &&
-					! isset( $dependency_script_modules[ $dependency['id'] ] )
-					) {
-						$dependencies[ $dependency['id'] ] = $this->registered[ $dependency['id'] ];
+				if ( isset( $this->registered[ $id ] ) ) {
+					foreach ( $this->registered[ $id ]['dependencies'] as $dependency ) {
+						if (
+							in_array( $dependency['import'], $import_types, true ) &&
+							isset( $this->registered[ $dependency['id'] ] ) &&
+							! isset( $dependency_script_modules[ $dependency['id'] ] )
+						) {
+							$dependencies[ $dependency['id'] ] = $this->registered[ $dependency['id'] ];
+						}
 					}
 				}
 				return array_merge( $dependency_script_modules, $dependencies, $this->get_dependencies( array_keys( $dependencies ), $import_types ) );
@@ -394,6 +451,75 @@ function ( $dependency_script_modules, $id ) use ( $import_types ) {
 		);
 	}
 
+	/**
+	 * Gets all dependents of a script module.
+	 *
+	 * This is not recursive.
+	 *
+	 * @since 6.9.0
+	 *
+	 * @see WP_Scripts::get_dependents()
+	 *
+	 * @param string $id The script ID.
+	 * @return string[] Script module IDs.
+	 */
+	private function get_dependents( string $id ): array {
+		// Check if dependents map for the handle in question is present. If so, use it.
+		if ( isset( $this->dependents_map[ $id ] ) ) {
+			return $this->dependents_map[ $id ];
+		}
+
+		$dependents = array();
+
+		// Iterate over all registered scripts, finding dependents of the script passed to this method.
+		foreach ( $this->registered as $registered_id => $args ) {
+			if ( in_array( $id, wp_list_pluck( $args['dependencies'], 'id' ), true ) ) {
+				$dependents[] = $registered_id;
+			}
+		}
+
+		// Add the module's dependents to the map to ease future lookups.
+		$this->dependents_map[ $id ] = $dependents;
+
+		return $dependents;
+	}
+
+	/**
+	 * Gets all recursive dependents of a script module.
+	 *
+	 * @since 6.9.0
+	 *
+	 * @see WP_Scripts::get_dependents()
+	 *
+	 * @param string $id The script ID.
+	 * @return string[] Script module IDs.
+	 */
+	private function get_recursive_dependents( string $id ): array {
+		$get = function ( string $id, array $checked = array() ) use ( &$get ): array {
+
+			// If by chance an unregistered script module is checked or there is a recursive dependency, return early.
+			if ( ! isset( $this->registered[ $id ] ) || isset( $checked[ $id ] ) ) {
+				return array();
+			}
+
+			// Mark this script module as checked to guard against infinite recursion.
+			$checked[ $id ] = true;
+
+			$dependents = array();
+			foreach ( $this->get_dependents( $id ) as $dependent ) {
+				$dependents = array_merge(
+					$dependents,
+					array( $dependent ),
+					$get( $dependent, $checked )
+				);
+			}
+
+			return $dependents;
+		};
+
+		return array_unique( $get( $id ) );
+	}
+
 	/**
 	 * Gets the versioned URL for a script module src.
 	 *
diff --git a/src/wp-includes/class-wp-scripts.php b/src/wp-includes/class-wp-scripts.php
index 71e85a3009577..61ad4c8fbd630 100644
--- a/src/wp-includes/class-wp-scripts.php
+++ b/src/wp-includes/class-wp-scripts.php
@@ -127,7 +127,7 @@ class WP_Scripts extends WP_Dependencies {
 	 * Used to optimize recursive dependency tree checks.
 	 *
 	 * @since 6.3.0
-	 * @var array
+	 * @var array<string, string[]>
 	 */
 	private $dependents_map = array();
 
@@ -439,9 +439,24 @@ public function do_item( $handle, $group = false ) {
 		if ( $intended_strategy ) {
 			$attr['data-wp-strategy'] = $intended_strategy;
 		}
-		if ( isset( $obj->extra['fetchpriority'] ) && 'auto' !== $obj->extra['fetchpriority'] && $this->is_valid_fetchpriority( $obj->extra['fetchpriority'] ) ) {
-			$attr['fetchpriority'] = $obj->extra['fetchpriority'];
+
+		// Determine fetchpriority.
+		$original_fetchpriority = isset( $obj->extra['fetchpriority'] ) ? $obj->extra['fetchpriority'] : null;
+		if ( null === $original_fetchpriority || ! $this->is_valid_fetchpriority( $original_fetchpriority ) ) {
+			$original_fetchpriority = 'auto';
+		}
+		$actual_fetchpriority = $this->get_highest_fetchpriority_with_dependents( $handle );
+		if ( null === $actual_fetchpriority ) {
+			// If null, it's likely this script was not explicitly enqueued, so in this case use the original priority.
+			$actual_fetchpriority = $original_fetchpriority;
+		}
+		if ( is_string( $actual_fetchpriority ) && 'auto' !== $actual_fetchpriority ) {
+			$attr['fetchpriority'] = $actual_fetchpriority;
 		}
+		if ( $original_fetchpriority !== $actual_fetchpriority ) {
+			$attr['data-wp-fetchpriority'] = $original_fetchpriority;
+		}
+
 		$tag  = $translations . $ie_conditional_prefix . $before_script;
 		$tag .= wp_get_script_tag( $attr );
 		$tag .= $after_script . $ie_conditional_suffix;
@@ -898,6 +913,8 @@ public function add_data( $handle, $key, $value ) {
 	/**
 	 * Gets all dependents of a script.
 	 *
+	 * This is not recursive.
+	 *
 	 * @since 6.3.0
 	 *
 	 * @param string $handle The script handle.
@@ -1051,6 +1068,62 @@ private function filter_eligible_strategies( $handle, $eligible_strategies = nul
 		return $eligible_strategies;
 	}
 
+	/**
+	 * Gets the highest fetch priority for a given script and all of its dependent scripts.
+	 *
+	 * @since 6.9.0
+	 * @see self::filter_eligible_strategies()
+	 * @see WP_Script_Modules::get_highest_fetchpriority_with_dependents()
+	 *
+	 * @param string              $handle  Script module ID.
+	 * @param array<string, true> $checked Optional. An array of already checked script handles, used to avoid recursive loops.
+	 * @return string|null Highest fetch priority for the script and its dependents.
+	 */
+	private function get_highest_fetchpriority_with_dependents( string $handle, array $checked = array() ): ?string {
+		// If there is a recursive dependency, return early.
+		if ( isset( $checked[ $handle ] ) ) {
+			return null;
+		}
+
+		// Mark this handle as checked to guard against infinite recursion.
+		$checked[ $handle ] = true;
+
+		// Abort if the script is not enqueued or a dependency of an enqueued script.
+		if ( ! $this->query( $handle, 'enqueued' ) ) {
+			return null;
+		}
+
+		$fetchpriority = $this->get_data( $handle, 'fetchpriority' );
+		if ( ! $this->is_valid_fetchpriority( $fetchpriority ) ) {
+			$fetchpriority = 'auto';
+		}
+
+		static $priorities   = array(
+			'low',
+			'auto',
+			'high',
+		);
+		$high_priority_index = count( $priorities ) - 1;
+
+		$highest_priority_index = (int) array_search( $fetchpriority, $priorities, true );
+		if ( $highest_priority_index !== $high_priority_index ) {
+			foreach ( $this->get_dependents( $handle ) as $dependent_handle ) {
+				$dependent_priority = $this->get_highest_fetchpriority_with_dependents( $dependent_handle, $checked );
+				if ( is_string( $dependent_priority ) ) {
+					$highest_priority_index = max(
+						$highest_priority_index,
+						(int) array_search( $dependent_priority, $priorities, true )
+					);
+					if ( $highest_priority_index === $high_priority_index ) {
+						break;
+					}
+				}
+			}
+		}
+
+		return $priorities[ $highest_priority_index ];
+	}
+
 	/**
 	 * Gets data for inline scripts registered for a specific handle.
 	 *
diff --git a/src/wp-includes/script-modules.php b/src/wp-includes/script-modules.php
index 0d284833bea09..82e7635f1c538 100644
--- a/src/wp-includes/script-modules.php
+++ b/src/wp-includes/script-modules.php
@@ -181,9 +181,21 @@ function wp_default_script_modules() {
 				break;
 		}
 
-		// The Interactivity API is designed with server-side rendering as its primary goal, so all of its script modules should be loaded with low fetch priority since they should not be needed in the critical rendering path.
+		/*
+		 * The Interactivity API is designed with server-side rendering as its primary goal, so all of its script modules
+		 * should be loaded with low fetchpriority since they should not be needed in the critical rendering path.
+		 * Also, the @wordpress/a11y script module is intended to be used as a dynamic import dependency, in which case
+		 * the fetchpriority is irrelevant. See <https://make.wordpress.org/core/2024/10/14/updates-to-script-modules-in-6-7/>.
+		 * However, in case it is added as a static import dependency, the fetchpriority is explicitly set to be 'low'
+		 * since the module should not be involved in the critical rendering path, and if it is, its fetchpriority will
+		 * be bumped to match the fetchpriority of the dependent script.
+		 */
 		$args = array();
-		if ( str_starts_with( $script_module_id, '@wordpress/interactivity' ) || str_starts_with( $script_module_id, '@wordpress/block-library' ) ) {
+		if (
+			str_starts_with( $script_module_id, '@wordpress/interactivity' ) ||
+			str_starts_with( $script_module_id, '@wordpress/block-library' ) ||
+			'@wordpress/a11y' === $script_module_id
+		) {
 			$args['fetchpriority'] = 'low';
 		}
 
diff --git a/tests/phpunit/tests/dependencies/scripts.php b/tests/phpunit/tests/dependencies/scripts.php
index c7a0d473a8221..bd4cbd27a49b4 100644
--- a/tests/phpunit/tests/dependencies/scripts.php
+++ b/tests/phpunit/tests/dependencies/scripts.php
@@ -1232,10 +1232,11 @@ public function test_defer_with_async_dependent() {
 				'fetchpriority' => 'high',
 			)
 		);
+		// Note: All of these scripts have fetchpriority=high because the leaf dependent script has that fetch priority.
 		$output    = get_echo( 'wp_print_scripts' );
-		$expected  = "<script type='text/javascript' src='/main-script-d4.js' id='main-script-d4-js' defer='defer' data-wp-strategy='defer'></script>\n";
-		$expected .= "<script type='text/javascript' src='/dependent-script-d4-1.js' id='dependent-script-d4-1-js' defer='defer' data-wp-strategy='defer'></script>\n";
-		$expected .= "<script type='text/javascript' src='/dependent-script-d4-2.js' id='dependent-script-d4-2-js' defer='defer' data-wp-strategy='async' fetchpriority='low'></script>\n";
+		$expected  = "<script type='text/javascript' src='/main-script-d4.js'        id='main-script-d4-js'        defer='defer' data-wp-strategy='defer' fetchpriority='high' data-wp-fetchpriority='auto'></script>\n";
+		$expected .= "<script type='text/javascript' src='/dependent-script-d4-1.js' id='dependent-script-d4-1-js' defer='defer' data-wp-strategy='defer' fetchpriority='high' data-wp-fetchpriority='auto'></script>\n";
+		$expected .= "<script type='text/javascript' src='/dependent-script-d4-2.js' id='dependent-script-d4-2-js' defer='defer' data-wp-strategy='async' fetchpriority='high' data-wp-fetchpriority='low'></script>\n";
 		$expected .= "<script type='text/javascript' src='/dependent-script-d4-3.js' id='dependent-script-d4-3-js' defer='defer' data-wp-strategy='defer' fetchpriority='high'></script>\n";
 
 		$this->assertEqualHTML( $expected, $output, '<body>', 'Scripts registered as defer but that have dependents that are async are expected to have said dependents deferred.' );
@@ -1343,6 +1344,150 @@ public function test_invalid_fetchpriority_on_alias() {
 		$this->assertArrayNotHasKey( 'fetchpriority', wp_scripts()->registered['alias']->extra );
 	}
 
+	/**
+	 * Data provider.
+	 *
+	 * @return array<string, array{enqueues: string[], expected: string}>
+	 */
+	public function data_provider_to_test_fetchpriority_bumping(): array {
+		return array(
+			'enqueue_bajo' => array(
+				'enqueues' => array( 'bajo' ),
+				'expected' => '<script fetchpriority="low" id="bajo-js" src="/bajo.js" type="text/javascript"></script>',
+			),
+			'enqueue_auto' => array(
+				'enqueues' => array( 'auto' ),
+				'expected' => '
+					<script type="text/javascript" src="/bajo.js" id="bajo-js" data-wp-fetchpriority="low"></script>
+					<script type="text/javascript" src="/auto.js" id="auto-js"></script>
+				',
+			),
+			'enqueue_alto' => array(
+				'enqueues' => array( 'alto' ),
+				'expected' => '
+					<script type="text/javascript" src="/bajo.js" id="bajo-js" fetchpriority="high" data-wp-fetchpriority="low"></script>
+					<script type="text/javascript" src="/auto.js" id="auto-js" fetchpriority="high" data-wp-fetchpriority="auto"></script>
+					<script type="text/javascript" src="/alto.js" id="alto-js" fetchpriority="high"></script>
+				',
+			),
+		);
+	}
+
+	/**
+	 * Tests a higher fetchpriority on a dependent script module causes the fetchpriority of a dependency script module to be bumped.
+	 *
+	 * @ticket 61734
+	 *
+	 * @covers WP_Scripts::get_dependents
+	 * @covers WP_Scripts::get_highest_fetchpriority_with_dependents
+	 * @covers WP_Scripts::do_item
+	 *
+	 * @dataProvider data_provider_to_test_fetchpriority_bumping
+	 */
+	public function test_fetchpriority_bumping( array $enqueues, string $expected ) {
+		wp_register_script( 'bajo', '/bajo.js', array(), null, array( 'fetchpriority' => 'low' ) );
+		wp_register_script( 'auto', '/auto.js', array( 'bajo' ), null, array( 'fetchpriority' => 'auto' ) );
+		wp_register_script( 'alto', '/alto.js', array( 'auto' ), null, array( 'fetchpriority' => 'high' ) );
+
+		foreach ( $enqueues as $enqueue ) {
+			wp_enqueue_script( $enqueue );
+		}
+
+		$actual = get_echo( 'wp_print_scripts' );
+		$this->assertEqualHTML( $expected, $actual, '<body>', "Snapshot:\n$actual" );
+	}
+
+	/**
+	 * Tests bumping fetchpriority with complex dependency graph.
+	 *
+	 * @ticket 61734
+	 * @link https://github.com/WordPress/wordpress-develop/pull/9770#issuecomment-3280065818
+	 *
+	 * @covers WP_Scripts::get_dependents
+	 * @covers WP_Scripts::get_highest_fetchpriority_with_dependents
+	 * @covers WP_Scripts::do_item
+	 */
+	public function test_fetchpriority_bumping_a_to_z() {
+		wp_register_script( 'a', '/a.js', array( 'b' ), null, array( 'fetchpriority' => 'low' ) );
+		wp_register_script( 'b', '/b.js', array( 'c' ), null, array( 'fetchpriority' => 'auto' ) );
+		wp_register_script( 'c', '/c.js', array( 'd', 'e' ), null, array( 'fetchpriority' => 'auto' ) );
+		wp_register_script( 'd', '/d.js', array( 'z' ), null, array( 'fetchpriority' => 'high' ) );
+		wp_register_script( 'e', '/e.js', array(), null, array( 'fetchpriority' => 'auto' ) );
+
+		wp_register_script( 'x', '/x.js', array( 'd', 'y' ), null, array( 'fetchpriority' => 'high' ) );
+		wp_register_script( 'y', '/y.js', array( 'z' ), null, array( 'fetchpriority' => 'auto' ) );
+		wp_register_script( 'z', '/z.js', array(), null, array( 'fetchpriority' => 'auto' ) );
+
+		wp_enqueue_script( 'a' );
+		wp_enqueue_script( 'x' );
+
+		$actual   = get_echo( 'wp_print_scripts' );
+		$expected = '
+			<script type="text/javascript" src="/z.js" id="z-js" fetchpriority="high" data-wp-fetchpriority="auto"></script>
+			<script type="text/javascript" src="/d.js" id="d-js" fetchpriority="high"></script>
+			<script type="text/javascript" src="/e.js" id="e-js"></script>
+			<script type="text/javascript" src="/c.js" id="c-js"></script>
+			<script type="text/javascript" src="/b.js" id="b-js"></script>
+			<script type="text/javascript" src="/a.js" id="a-js" fetchpriority="low"></script>
+			<script type="text/javascript" src="/y.js" id="y-js" fetchpriority="high" data-wp-fetchpriority="auto"></script>
+			<script type="text/javascript" src="/x.js" id="x-js" fetchpriority="high"></script>
+		';
+		$this->assertEqualHTML( $expected, $actual, '<body>', "Snapshot:\n$actual" );
+	}
+
+	/**
+	 * Tests that printing a script without enqueueing has the same output as when it is enqueued.
+	 *
+	 * @ticket 61734
+	 *
+	 * @covers WP_Scripts::do_item
+	 * @covers WP_Scripts::do_items
+	 * @covers ::wp_default_scripts
+	 *
+	 * @dataProvider data_provider_enqueue_or_not_to_enqueue
+	 */
+	public function test_printing_default_script_comment_reply_enqueued_or_not_enqueued( bool $enqueue ) {
+		$wp_scripts = wp_scripts();
+		wp_default_scripts( $wp_scripts );
+
+		$this->assertArrayHasKey( 'comment-reply', $wp_scripts->registered );
+		$wp_scripts->registered['comment-reply']->ver = null;
+		$this->assertArrayHasKey( 'fetchpriority', $wp_scripts->registered['comment-reply']->extra );
+		$this->assertSame( 'low', $wp_scripts->registered['comment-reply']->extra['fetchpriority'] );
+		$this->assertArrayHasKey( 'strategy', $wp_scripts->registered['comment-reply']->extra );
+		$this->assertSame( 'async', $wp_scripts->registered['comment-reply']->extra['strategy'] );
+		if ( $enqueue ) {
+			wp_enqueue_script( 'comment-reply' );
+			$markup = get_echo( array( $wp_scripts, 'do_items' ), array( false ) );
+		} else {
+			$markup = get_echo( array( $wp_scripts, 'do_items' ), array( array( 'comment-reply' ) ) );
+		}
+
+		$this->assertEqualHTML(
+			sprintf(
+				'<script type="text/javascript" src="%s" id="comment-reply-js" async="async" data-wp-strategy="async" fetchpriority="low"></script>',
+				includes_url( 'js/comment-reply.js' )
+			),
+			$markup
+		);
+	}
+
+	/**
+	 * Data provider for test_default_scripts_comment_reply_not_enqueued.
+	 *
+	 * @return array[]
+	 */
+	public static function data_provider_enqueue_or_not_to_enqueue(): array {
+		return array(
+			'not_enqueued' => array(
+				false,
+			),
+			'enqueued'     => array(
+				true,
+			),
+		);
+	}
+
 	/**
 	 * Tests that scripts registered as defer become blocking when their dependents chain are all blocking.
 	 *
diff --git a/tests/phpunit/tests/script-modules/wpScriptModules.php b/tests/phpunit/tests/script-modules/wpScriptModules.php
index a912a0e95b268..97be85f071489 100644
--- a/tests/phpunit/tests/script-modules/wpScriptModules.php
+++ b/tests/phpunit/tests/script-modules/wpScriptModules.php
@@ -67,9 +67,17 @@ public function get_enqueued_script_modules(): array {
 
 			$id             = preg_replace( '/-js-module$/', '', (string) $p->get_attribute( 'id' ) );
 			$fetchpriority  = $p->get_attribute( 'fetchpriority' );
-			$modules[ $id ] = array(
-				'url'           => $p->get_attribute( 'src' ),
-				'fetchpriority' => is_string( $fetchpriority ) ? $fetchpriority : 'auto',
+			$modules[ $id ] = array_merge(
+				array(
+					'url'           => $p->get_attribute( 'src' ),
+					'fetchpriority' => is_string( $fetchpriority ) ? $fetchpriority : 'auto',
+				),
+				...array_map(
+					static function ( $attribute_name ) use ( $p ) {
+						return array( $attribute_name => $p->get_attribute( $attribute_name ) );
+					},
+					$p->get_attribute_names_with_prefix( 'data-' )
+				)
 			);
 		}
 
@@ -112,9 +120,17 @@ public function get_preloaded_script_modules(): array {
 
 			$id              = preg_replace( '/-js-modulepreload$/', '', $p->get_attribute( 'id' ) );
 			$fetchpriority   = $p->get_attribute( 'fetchpriority' );
-			$preloads[ $id ] = array(
-				'url'           => $p->get_attribute( 'href' ),
-				'fetchpriority' => is_string( $fetchpriority ) ? $fetchpriority : 'auto',
+			$preloads[ $id ] = array_merge(
+				array(
+					'url'           => $p->get_attribute( 'href' ),
+					'fetchpriority' => is_string( $fetchpriority ) ? $fetchpriority : 'auto',
+				),
+				...array_map(
+					static function ( $attribute_name ) use ( $p ) {
+						return array( $attribute_name => $p->get_attribute( $attribute_name ) );
+					},
+					$p->get_attribute_names_with_prefix( 'data-' )
+				)
 			);
 		}
 
@@ -271,15 +287,17 @@ public function test_comprehensive_methods( bool $use_global_function, bool $onl
 				'preload_links' => array(
 					'b-dep'        => array(
 						'url'           => '/b-dep.js?ver=99.9.9',
-						'fetchpriority' => 'auto',
+						'fetchpriority' => 'low', // Propagates from 'b'.
 					),
 					'c-dep'        => array(
-						'url'           => '/c-static.js?ver=99.9.9',
-						'fetchpriority' => 'low',
+						'url'                   => '/c-static.js?ver=99.9.9',
+						'fetchpriority'         => 'auto', // Not 'low' because the dependent script 'c' has a fetchpriority of 'auto'.
+						'data-wp-fetchpriority' => 'low',
 					),
 					'c-static-dep' => array(
-						'url'           => '/c-static-dep.js?ver=99.9.9',
-						'fetchpriority' => 'high',
+						'url'                   => '/c-static-dep.js?ver=99.9.9',
+						'fetchpriority'         => 'auto', // Propagated from 'c'.
+						'data-wp-fetchpriority' => 'high',
 					),
 					'd-static-dep' => array(
 						'url'           => '/d-static-dep.js?ver=99.9.9',
@@ -732,6 +750,7 @@ public function test_wp_enqueue_preloaded_static_dependencies() {
 					'import' => 'dynamic',
 				),
 			)
+			// Note: The default fetchpriority=auto is upgraded to high because the dependent script module 'static-dep' has a high fetch priority.
 		);
 		$this->script_modules->register(
 			'static-dep',
@@ -759,9 +778,9 @@ public function test_wp_enqueue_preloaded_static_dependencies() {
 
 		$this->assertCount( 2, $preloaded_script_modules );
 		$this->assertStringStartsWith( '/static-dep.js', $preloaded_script_modules['static-dep']['url'] );
-		$this->assertSame( 'high', $preloaded_script_modules['static-dep']['fetchpriority'] );
+		$this->assertSame( 'auto', $preloaded_script_modules['static-dep']['fetchpriority'] ); // Not 'high'
 		$this->assertStringStartsWith( '/nested-static-dep.js', $preloaded_script_modules['nested-static-dep']['url'] );
-		$this->assertSame( 'auto', $preloaded_script_modules['nested-static-dep']['fetchpriority'] );
+		$this->assertSame( 'auto', $preloaded_script_modules['nested-static-dep']['fetchpriority'] ); // Auto because the enqueued script foo has the fetchpriority of auto.
 		$this->assertArrayNotHasKey( 'dynamic-dep', $preloaded_script_modules );
 		$this->assertArrayNotHasKey( 'nested-dynamic-dep', $preloaded_script_modules );
 		$this->assertArrayNotHasKey( 'no-dep', $preloaded_script_modules );
@@ -971,7 +990,7 @@ public function test_version_is_propagated_correctly() {
 
 		$preloaded_script_modules = $this->get_preloaded_script_modules();
 		$this->assertSame( '/dep.js?ver=2.0', $preloaded_script_modules['dep']['url'] );
-		$this->assertSame( 'high', $preloaded_script_modules['dep']['fetchpriority'] );
+		$this->assertSame( 'auto', $preloaded_script_modules['dep']['fetchpriority'] ); // Because 'foo' has a priority of 'auto'.
 	}
 
 	/**
@@ -1343,6 +1362,319 @@ public function test_set_fetchpriority_with_invalid_value() {
 		$this->assertSame( 'auto', $registered_modules['foo']['fetchpriority'] );
 	}
 
+	/**
+	 * Data provider.
+	 *
+	 * @return array<string, array{enqueues: string[], expected: array}>
+	 */
+	public function data_provider_to_test_fetchpriority_bumping(): array {
+		return array(
+			'enqueue_bajo' => array(
+				'enqueues' => array( 'bajo' ),
+				'expected' => array(
+					'preload_links' => array(),
+					'script_tags'   => array(
+						'bajo' => array(
+							'url'                   => '/bajo.js',
+							'fetchpriority'         => 'high',
+							'data-wp-fetchpriority' => 'low',
+						),
+					),
+					'import_map'    => array(
+						'dyno' => '/dyno.js',
+					),
+				),
+			),
+			'enqueue_auto' => array(
+				'enqueues' => array( 'auto' ),
+				'expected' => array(
+					'preload_links' => array(
+						'bajo' => array(
+							'url'                   => '/bajo.js',
+							'fetchpriority'         => 'auto',
+							'data-wp-fetchpriority' => 'low',
+						),
+					),
+					'script_tags'   => array(
+						'auto' => array(
+							'url'                   => '/auto.js',
+							'fetchpriority'         => 'high',
+							'data-wp-fetchpriority' => 'auto',
+						),
+					),
+					'import_map'    => array(
+						'bajo' => '/bajo.js',
+						'dyno' => '/dyno.js',
+					),
+				),
+			),
+			'enqueue_alto' => array(
+				'enqueues' => array( 'alto' ),
+				'expected' => array(
+					'preload_links' => array(
+						'auto' => array(
+							'url'           => '/auto.js',
+							'fetchpriority' => 'high',
+						),
+						'bajo' => array(
+							'url'                   => '/bajo.js',
+							'fetchpriority'         => 'high',
+							'data-wp-fetchpriority' => 'low',
+						),
+					),
+					'script_tags'   => array(
+						'alto' => array(
+							'url'           => '/alto.js',
+							'fetchpriority' => 'high',
+						),
+					),
+					'import_map'    => array(
+						'auto' => '/auto.js',
+						'bajo' => '/bajo.js',
+						'dyno' => '/dyno.js',
+					),
+				),
+			),
+		);
+	}
+
+	/**
+	 * Tests a higher fetchpriority on a dependent script module causes the fetchpriority of a dependency script module to be bumped.
+	 *
+	 * @ticket 61734
+	 *
+	 * @covers WP_Script_Modules::print_enqueued_script_modules
+	 * @covers WP_Script_Modules::get_dependents
+	 * @covers WP_Script_Modules::get_recursive_dependents
+	 * @covers WP_Script_Modules::get_highest_fetchpriority
+	 * @covers WP_Script_Modules::print_script_module_preloads
+	 *
+	 * @dataProvider data_provider_to_test_fetchpriority_bumping
+	 */
+	public function test_fetchpriority_bumping( array $enqueues, array $expected ) {
+		$this->script_modules->register(
+			'dyno',
+			'/dyno.js',
+			array(),
+			null,
+			array( 'fetchpriority' => 'low' ) // This won't show up anywhere since it is a dynamic import dependency.
+		);
+
+		$this->script_modules->register(
+			'bajo',
+			'/bajo.js',
+			array(
+				array(
+					'id'     => 'dyno',
+					'import' => 'dynamic',
+				),
+			),
+			null,
+			array( 'fetchpriority' => 'low' )
+		);
+
+		$this->script_modules->register(
+			'auto',
+			'/auto.js',
+			array(
+				array(
+					'id'     => 'bajo',
+					'import' => 'static',
+				),
+			),
+			null,
+			array( 'fetchpriority' => 'auto' )
+		);
+		$this->script_modules->register(
+			'alto',
+			'/alto.js',
+			array( 'auto' ),
+			null,
+			array( 'fetchpriority' => 'high' )
+		);
+
+		foreach ( $enqueues as $enqueue ) {
+			$this->script_modules->enqueue( $enqueue );
+		}
+
+		$actual = array(
+			'preload_links' => $this->get_preloaded_script_modules(),
+			'script_tags'   => $this->get_enqueued_script_modules(),
+			'import_map'    => $this->get_import_map(),
+		);
+		$this->assertSame(
+			$expected,
+			$actual,
+			"Snapshot:\n" . var_export( $actual, true )
+		);
+	}
+
+	/**
+	 * Tests bumping fetchpriority with complex dependency graph.
+	 *
+	 * @ticket 61734
+	 * @link https://github.com/WordPress/wordpress-develop/pull/9770#issuecomment-3280065818
+	 *
+	 * @covers WP_Script_Modules::print_enqueued_script_modules
+	 * @covers WP_Script_Modules::get_dependents
+	 * @covers WP_Script_Modules::get_recursive_dependents
+	 * @covers WP_Script_Modules::get_highest_fetchpriority
+	 * @covers WP_Script_Modules::print_script_module_preloads
+	 */
+	public function test_fetchpriority_bumping_a_to_z() {
+		wp_register_script_module( 'a', '/a.js', array( 'b' ), null, array( 'fetchpriority' => 'low' ) );
+		wp_register_script_module( 'b', '/b.js', array( 'c' ), null, array( 'fetchpriority' => 'auto' ) );
+		wp_register_script_module( 'c', '/c.js', array( 'd', 'e' ), null, array( 'fetchpriority' => 'auto' ) );
+		wp_register_script_module( 'd', '/d.js', array( 'z' ), null, array( 'fetchpriority' => 'high' ) );
+		wp_register_script_module( 'e', '/e.js', array(), null, array( 'fetchpriority' => 'auto' ) );
+
+		wp_register_script_module( 'x', '/x.js', array( 'd', 'y' ), null, array( 'fetchpriority' => 'high' ) );
+		wp_register_script_module( 'y', '/y.js', array( 'z' ), null, array( 'fetchpriority' => 'auto' ) );
+		wp_register_script_module( 'z', '/z.js', array(), null, array( 'fetchpriority' => 'auto' ) );
+
+		// The fetch priorities are derived from these enqueued dependents.
+		wp_enqueue_script_module( 'a' );
+		wp_enqueue_script_module( 'x' );
+
+		$actual   = get_echo( array( wp_script_modules(), 'print_script_module_preloads' ) );
+		$actual  .= get_echo( array( wp_script_modules(), 'print_enqueued_script_modules' ) );
+		$expected = '
+			<link rel="modulepreload" href="/b.js" id="b-js-modulepreload" fetchpriority="low">
+			<link rel="modulepreload" href="/c.js" id="c-js-modulepreload" fetchpriority="low">
+			<link rel="modulepreload" href="/d.js" id="d-js-modulepreload" fetchpriority="high">
+			<link rel="modulepreload" href="/e.js" id="e-js-modulepreload" fetchpriority="low">
+			<link rel="modulepreload" href="/z.js" id="z-js-modulepreload" fetchpriority="high">
+			<link rel="modulepreload" href="/y.js" id="y-js-modulepreload" fetchpriority="high">
+			<script type="module" src="/a.js" id="a-js-module" fetchpriority="low"></script>
+			<script type="module" src="/x.js" id="x-js-module" fetchpriority="high"></script>
+		';
+		$this->assertEqualHTML( $expected, $actual, '<body>', "Snapshot:\n$actual" );
+	}
+
+	/**
+	 * Tests bumping fetchpriority with complex dependency graph.
+	 *
+	 * @ticket 61734
+	 * @link https://github.com/WordPress/wordpress-develop/pull/9770#issuecomment-3284266884
+	 *
+	 * @covers WP_Script_Modules::print_enqueued_script_modules
+	 * @covers WP_Script_Modules::get_dependents
+	 * @covers WP_Script_Modules::get_recursive_dependents
+	 * @covers WP_Script_Modules::get_highest_fetchpriority
+	 * @covers WP_Script_Modules::print_script_module_preloads
+	 */
+	public function test_fetchpriority_propagation() {
+		// The high fetchpriority for this module will be disregarded because its enqueued dependent has a non-high priority.
+		wp_register_script_module( 'a', '/a.js', array( 'd', 'e' ), null, array( 'fetchpriority' => 'high' ) );
+		wp_register_script_module( 'b', '/b.js', array( 'e' ), null );
+		wp_register_script_module( 'c', '/c.js', array( 'e', 'f' ), null );
+		wp_register_script_module( 'd', '/d.js', array(), null );
+		// The low fetchpriority for this module will be disregarded because its enqueued dependent has a non-low priority.
+		wp_register_script_module( 'e', '/e.js', array(), null, array( 'fetchpriority' => 'low' ) );
+		wp_register_script_module( 'f', '/f.js', array(), null );
+
+		wp_register_script_module( 'x', '/x.js', array( 'a' ), null, array( 'fetchpriority' => 'low' ) );
+		wp_register_script_module( 'y', '/y.js', array( 'b' ), null, array( 'fetchpriority' => 'auto' ) );
+		wp_register_script_module( 'z', '/z.js', array( 'c' ), null, array( 'fetchpriority' => 'high' ) );
+
+		wp_enqueue_script_module( 'x' );
+		wp_enqueue_script_module( 'y' );
+		wp_enqueue_script_module( 'z' );
+
+		$actual   = get_echo( array( wp_script_modules(), 'print_script_module_preloads' ) );
+		$actual  .= get_echo( array( wp_script_modules(), 'print_enqueued_script_modules' ) );
+		$expected = '
+			<link rel="modulepreload" href="/a.js" id="a-js-modulepreload" fetchpriority="low" data-wp-fetchpriority="high">
+			<link rel="modulepreload" href="/d.js" id="d-js-modulepreload" fetchpriority="low">
+			<link rel="modulepreload" href="/e.js" id="e-js-modulepreload" fetchpriority="high" data-wp-fetchpriority="low">
+			<link rel="modulepreload" href="/b.js" id="b-js-modulepreload">
+			<link rel="modulepreload" href="/c.js" id="c-js-modulepreload" fetchpriority="high">
+			<link rel="modulepreload" href="/f.js" id="f-js-modulepreload" fetchpriority="high">
+			<script type="module" src="/x.js" id="x-js-module" fetchpriority="low"></script>
+			<script type="module" src="/y.js" id="y-js-module"></script>
+			<script type="module" src="/z.js" id="z-js-module" fetchpriority="high"></script>
+		';
+		$this->assertEqualHTML( $expected, $actual, '<body>', "Snapshot:\n$actual" );
+	}
+
+	/**
+	 * Tests that default script modules are printed as expected.
+	 *
+	 * @covers ::wp_default_script_modules
+	 * @covers WP_Script_Modules::print_script_module_preloads
+	 * @covers WP_Script_Modules::print_enqueued_script_modules
+	 */
+	public function test_default_script_modules() {
+		wp_default_script_modules();
+		wp_enqueue_script_module( '@wordpress/a11y' );
+		wp_enqueue_script_module( '@wordpress/block-library/navigation/view' );
+
+		$actual  = get_echo( array( wp_script_modules(), 'print_script_module_preloads' ) );
+		$actual .= get_echo( array( wp_script_modules(), 'print_enqueued_script_modules' ) );
+
+		$actual = $this->normalize_markup_for_snapshot( $actual );
+
+		$expected = '
+			<link rel="modulepreload" href="/wp-includes/js/dist/script-modules/interactivity/debug.min.js" id="@wordpress/interactivity-js-modulepreload" fetchpriority="low">
+			<script type="module" src="/wp-includes/js/dist/script-modules/a11y/index.min.js" id="@wordpress/a11y-js-module" fetchpriority="low"></script>
+			<script type="module" src="/wp-includes/js/dist/script-modules/block-library/navigation/view.min.js" id="@wordpress/block-library/navigation/view-js-module" fetchpriority="low"></script>
+		';
+		$this->assertEqualHTML( $expected, $actual, '<body>', "Snapshot:\n$actual" );
+	}
+
+	/**
+	 * Tests that a dependent with high priority for default script modules with a low fetch priority are printed as expected.
+	 *
+	 * @covers ::wp_default_script_modules
+	 * @covers WP_Script_Modules::print_script_module_preloads
+	 * @covers WP_Script_Modules::print_enqueued_script_modules
+	 */
+	public function test_dependent_of_default_script_modules() {
+		wp_default_script_modules();
+		wp_enqueue_script_module(
+			'super-important',
+			'/super-important-module.js',
+			array( '@wordpress/a11y', '@wordpress/block-library/navigation/view' ),
+			null,
+			array( 'fetchpriority' => 'high' )
+		);
+
+		$actual  = get_echo( array( wp_script_modules(), 'print_script_module_preloads' ) );
+		$actual .= get_echo( array( wp_script_modules(), 'print_enqueued_script_modules' ) );
+
+		$actual = $this->normalize_markup_for_snapshot( $actual );
+
+		$expected = '
+			<link rel="modulepreload" href="/wp-includes/js/dist/script-modules/a11y/index.min.js" id="@wordpress/a11y-js-modulepreload" fetchpriority="high" data-wp-fetchpriority="low">
+			<link rel="modulepreload" href="/wp-includes/js/dist/script-modules/block-library/navigation/view.min.js" id="@wordpress/block-library/navigation/view-js-modulepreload" fetchpriority="high" data-wp-fetchpriority="low">
+			<link rel="modulepreload" href="/wp-includes/js/dist/script-modules/interactivity/debug.min.js" id="@wordpress/interactivity-js-modulepreload" fetchpriority="high" data-wp-fetchpriority="low">
+			<script type="module" src="/super-important-module.js" id="super-important-js-module" fetchpriority="high"></script>
+		';
+		$this->assertEqualHTML( $expected, $actual, '<body>', "Snapshot:\n$actual" );
+	}
+
+	/**
+	 * Normalizes markup for snapshot.
+	 *
+	 * @param string $markup Markup.
+	 * @return string Normalized markup.
+	 */
+	private function normalize_markup_for_snapshot( string $markup ): string {
+		$processor = new WP_HTML_Tag_Processor( $markup );
+		$clean_url = static function ( string $url ): string {
+			$url = preg_replace( '#^https?://[^/]+#', '', $url );
+			return remove_query_arg( 'ver', $url );
+		};
+		while ( $processor->next_tag() ) {
+			if ( 'LINK' === $processor->get_tag() && is_string( $processor->get_attribute( 'href' ) ) ) {
+				$processor->set_attribute( 'href', $clean_url( $processor->get_attribute( 'href' ) ) );
+			} elseif ( 'SCRIPT' === $processor->get_tag() && is_string( $processor->get_attribute( 'src' ) ) ) {
+				$processor->set_attribute( 'src', $clean_url( $processor->get_attribute( 'src' ) ) );
+			}
+		}
+		return $processor->get_updated_html();
+	}
+
 	/**
 	 * Tests that directly manipulating the queue works as expected.
 	 *