diff --git a/src/wp-includes/abilities/class-wp-abilities-content.php b/src/wp-includes/abilities/class-wp-abilities-content.php
index 725301fd6a0f3..4a4b46b1690df 100644
--- a/src/wp-includes/abilities/class-wp-abilities-content.php
+++ b/src/wp-includes/abilities/class-wp-abilities-content.php
@@ -460,14 +460,16 @@ private function execute_content_query( $input = array() ) {
 				);
 			}
 
-			$author = $this->get_author_by_slug( $where['author_slug'], $post_type_object );
-			if ( ! $author ) {
+			if ( ! is_string( $where['author_slug'] ) ) {
 				return $this->invalid_filter_error(
 					'where[author_slug]',
 					/* translators: %s: Parameter. */
-					sprintf( __( 'The %s filter must be the slug of an existing user.' ), 'author_slug' )
+					sprintf( __( 'The %s filter must be a string.' ), 'author_slug' )
 				);
 			}
+
+			// A slug that names no user stays false, see below.
+			$author = get_user_by( 'slug', $where['author_slug'] );
 		}
 
 		/*
@@ -561,7 +563,7 @@ private function execute_content_query( $input = array() ) {
 			$query_args['post_name__in'] = $slugs;
 		}
 
-		if ( null !== $author ) {
+		if ( $author ) {
 			$query_args['author'] = $author->ID;
 		}
 
@@ -569,6 +571,14 @@ private function execute_content_query( $input = array() ) {
 			$query_args['post_parent'] = $parent;
 		}
 
+		/*
+		 * An author_slug that names no user matches no post, like IDs and slugs that name no
+		 * post, rather than failing the query.
+		 */
+		if ( false === $author ) {
+			return $this->prepare_output( array(), 0, 0 );
+		}
+
 		$query = new WP_Query( $query_args );
 		$total = $this->get_query_total( $query, $query_args, $page );
 
@@ -745,50 +755,6 @@ private function is_field_requested( string $path, array $fields ): bool {
 		return rest_is_field_included( $path, $fields );
 	}
 
-	/**
-	 * Looks up the user an author slug names.
-	 *
-	 * The slug is the user's nicename, which the REST API users endpoint returns as `slug`. It is
-	 * looked up as given, like that endpoint's `slug` filter, so the database collation decides
-	 * whether a variant in another case matches. A user the current user may not see is reported
-	 * like a missing one. The current user can see themselves, any user of the site when they can
-	 * list users, and authors with posts in a publicly viewable post type. A user who can edit
-	 * others' posts of the post type can also see any user of the site, since they may make any of
-	 * them the author, so for them the lookup does tell whether such an account exists.
-	 *
-	 * On multisite the lookup searches the whole network, so posts by authors who are not
-	 * members of the site, such as super admins, can still be filtered. Those users are only
-	 * visible as the current user or as authors with posts in a publicly viewable post type, so
-	 * the lookup does not tell whether an account exists elsewhere on the network.
-	 *
-	 * @since 7.2.0
-	 *
-	 * @param mixed        $slug             The author slug.
-	 * @param WP_Post_Type $post_type_object The post type the author is looked up for.
-	 * @return WP_User|null The user, or null when the slug does not name a visible user.
-	 */
-	private function get_author_by_slug( $slug, WP_Post_Type $post_type_object ): ?WP_User {
-		$user = is_string( $slug ) ? get_user_by( 'slug', $slug ) : false;
-		if ( ! $user ) {
-			return null;
-		}
-
-		if ( get_current_user_id() === $user->ID ) {
-			return $user;
-		}
-
-		// The capabilities only reveal users of the site, not of the whole network.
-		if ( is_user_member_of_blog( $user->ID )
-			&& ( current_user_can( 'list_users' ) || current_user_can( $post_type_object->cap->edit_others_posts ) )
-		) {
-			return $user;
-		}
-
-		$public_post_types = array_values( array_filter( get_post_types(), 'is_post_type_viewable' ) );
-
-		return ! empty( $public_post_types ) && count_user_posts( $user->ID, $public_post_types ) > 0 ? $user : null;
-	}
-
 	/**
 	 * Returns a post type exposed through the Abilities API.
 	 *
@@ -1198,7 +1164,7 @@ private function get_content_query_input_schema( array $post_types, array $statu
 						'author_slug' => array(
 							'type'        => 'string',
 							'minLength'   => 1,
-							'description' => __( "Filter by the author's user slug (nicename), as the REST API users endpoint returns it in `slug`. Only supported for post types that support authors." ),
+							'description' => __( "Filter by the author's user slug (nicename), as the REST API users endpoint returns it in `slug`. A slug that names no user matches no post. Only supported for post types that support authors." ),
 						),
 						'parent'      => array(
 							'type'        => 'integer',
diff --git a/tests/phpunit/tests/abilities-api/wpRegisterCoreContentAbility.php b/tests/phpunit/tests/abilities-api/wpRegisterCoreContentAbility.php
index 08c6df936aecb..e7632e1eb1bcb 100644
--- a/tests/phpunit/tests/abilities-api/wpRegisterCoreContentAbility.php
+++ b/tests/phpunit/tests/abilities-api/wpRegisterCoreContentAbility.php
@@ -5036,34 +5036,40 @@ public function test_malformed_date_is_null( string $field, string $column ): vo
 	}
 
 	/**
-	 * Returns author slugs that do not name a user.
+	 * An author_slug filter that is not a string is rejected rather than silently dropped,
+	 * which would widen the query to every author's posts.
 	 *
-	 * @return array<string, array{0: mixed}> The author slug filter value.
+	 * @ticket 66268
 	 */
-	public function data_author_slugs_that_name_no_user(): array {
-		return array(
-			'unknown slug' => array( 'no-such-user' ),
-			'not a string' => array( 5 ),
+	public function test_execute_callback_rejects_an_author_slug_that_is_not_a_string(): void {
+		$this->login_as( 'administrator' );
+		$execute = $this->get_ability_callbacks()['execute_callback'];
+
+		$result = $execute(
+			array(
+				'where' => array(
+					'type'        => 'post',
+					'author_slug' => 5,
+				),
+			)
+		);
+
+		$this->assertWPError( $result, 'An author_slug that is not a string must not silently widen the query to all authors.' );
+		$this->assertSame( 'content_invalid_filter', $result->get_error_code(), 'An author_slug that is not a string should fail as an invalid filter.' );
+		$this->assertSame(
+			array( 'where[author_slug]' => $result->get_error_message() ),
+			$result->get_error_data()['params'],
+			'The error data should map the malformed author_slug filter to the error message.'
 		);
 	}
 
 	/**
-	 * An author_slug filter that does not name a user is rejected rather than silently
-	 * dropped, which would widen the query to every author's posts.
+	 * An author_slug filter that names no user matches no post, rather than being dropped,
+	 * which would widen the query to every author's posts.
 	 *
 	 * @ticket 66268
-	 * @dataProvider data_author_slugs_that_name_no_user
-	 *
-	 * @param mixed $author_slug The author slug filter value.
 	 */
-	public function test_execute_callback_rejects_an_author_slug_that_names_no_user( $author_slug ): void {
-		wp_update_user(
-			array(
-				'ID'            => self::$user_ids['author'],
-				'user_nicename' => 'author-slug',
-			)
-		);
-
+	public function test_author_slug_filter_that_names_no_user_matches_no_post(): void {
 		$this->login_as( 'administrator' );
 		$execute = $this->get_ability_callbacks()['execute_callback'];
 
@@ -5071,18 +5077,12 @@ public function test_execute_callback_rejects_an_author_slug_that_names_no_user(
 			array(
 				'where' => array(
 					'type'        => 'post',
-					'author_slug' => $author_slug,
+					'author_slug' => 'no-such-user',
 				),
 			)
 		);
 
-		$this->assertWPError( $result, 'An author_slug that names no user must not silently widen the query to all authors.' );
-		$this->assertSame( 'content_invalid_filter', $result->get_error_code(), 'An unhonorable author_slug filter should fail closed as an invalid filter.' );
-		$this->assertSame(
-			array( 'where[author_slug]' => $result->get_error_message() ),
-			$result->get_error_data()['params'],
-			'The error data should map the unmatched author_slug filter to the error message.'
-		);
+		$this->assertSame( self::EMPTY_RESULT, $result, 'An author_slug that names no user should match no post.' );
 	}
 
 	/**
@@ -5664,14 +5664,13 @@ public function test_execute_callback_defaults_a_pagination_that_is_not_an_objec
 	}
 
 	/**
-	 * An author_slug filter names only users the current user may see: a user without
-	 * published posts is reported like a missing one to a subscriber, but not to an editor,
-	 * who can edit their posts.
+	 * An author_slug filter matches only the posts the current user may read, so a user
+	 * without such posts gives the same empty result as a slug that names no user.
 	 *
 	 * @ticket 66268
 	 * @since 7.2.0
 	 */
-	public function test_author_slug_filter_only_names_users_the_current_user_may_see(): void {
+	public function test_author_slug_filter_matches_no_post_for_a_user_without_readable_posts(): void {
 		$published_id = self::factory()->post->create( array( 'post_author' => self::$user_ids['author'] ) );
 		$draft_id     = self::factory()->post->create(
 			array(
@@ -5681,90 +5680,48 @@ public function test_author_slug_filter_only_names_users_the_current_user_may_se
 		);
 
 		$execute = $this->get_ability_callbacks()['execute_callback'];
-		$query   = static function ( array $statuses, int $user_id ) use ( $execute ) {
+		$query   = static function ( array $statuses, string $author_slug ) use ( $execute ) {
 			return $execute(
 				array(
 					'where'  => array(
 						'type'        => 'post',
 						'status'      => $statuses,
-						'author_slug' => get_userdata( $user_id )->user_nicename,
+						'author_slug' => $author_slug,
 					),
 					'fields' => array( 'id' ),
 				)
 			);
 		};
 
+		$author_slug           = get_userdata( self::$user_ids['author'] )->user_nicename;
+		$author_secondary_slug = get_userdata( self::$user_ids['author_secondary'] )->user_nicename;
+		$subscriber_slug       = get_userdata( self::$user_ids['subscriber'] )->user_nicename;
+
 		$this->login_as( 'subscriber' );
-		$public = $query( array( 'publish' ), self::$user_ids['author'] );
+		$public = $query( array( 'publish' ), $author_slug );
 		$this->assertIsArray( $public, 'A subscriber should filter by an author with published posts.' );
 		$this->assertSame( array( $published_id ), wp_list_pluck( $public['items'], 'id' ), 'The filter should return that author\'s posts.' );
-
-		$hidden = $query( array( 'publish' ), self::$user_ids['author_secondary'] );
-		$this->assertWPError( $hidden, 'A subscriber should not learn that an author without published posts exists.' );
-		$this->assertSame( 'content_invalid_filter', $hidden->get_error_code(), 'A hidden author should be reported like a missing one.' );
-		$this->assertSame(
-			array( 'where[author_slug]' => $hidden->get_error_message() ),
-			$hidden->get_error_data()['params'],
-			'The error data should map the hidden author_slug filter to the error message.'
-		);
+		$this->assertSame( self::EMPTY_RESULT, $query( array( 'publish' ), $author_secondary_slug ), 'A subscriber should get the empty result for an author without published posts.' );
+		$this->assertSame( self::EMPTY_RESULT, $query( array( 'publish' ), 'no-such-user' ), 'A subscriber should get the empty result for a slug that names no user.' );
 
 		$this->login_as( 'editor' );
-		$drafts = $query( array( 'draft' ), self::$user_ids['author_secondary'] );
+		$this->assertSame( self::EMPTY_RESULT, $query( array( 'publish' ), $subscriber_slug ), 'An editor should get the empty result for a user without posts.' );
+		$this->assertSame( self::EMPTY_RESULT, $query( array( 'publish' ), 'no-such-user' ), 'An editor should get the empty result for a slug that names no user.' );
+
+		$drafts = $query( array( 'draft' ), $author_secondary_slug );
 		$this->assertIsArray( $drafts, 'An editor should filter by an author without published posts.' );
 		$this->assertSame( array( $draft_id ), wp_list_pluck( $drafts['items'], 'id' ), 'The filter should return that author\'s drafts.' );
 	}
 
 	/**
-	 * For a post type with its own capabilities, an author_slug filter names a user without
-	 * published posts to the users who can edit others' posts of that post type, not to those
-	 * who can edit others' posts.
-	 *
-	 * @ticket 66268
-	 * @since 7.2.0
-	 */
-	public function test_author_slug_filter_follows_the_capabilities_of_the_queried_post_type(): void {
-		$this->register_post_type_with_own_capabilities();
-
-		$draft_id = self::factory()->post->create(
-			array(
-				'post_type'   => 'book',
-				'post_author' => self::$user_ids['author_secondary'],
-				'post_status' => 'draft',
-			)
-		);
-
-		$execute = $this->get_ability_callbacks()['execute_callback'];
-		$input   = array(
-			'where'  => array(
-				'type'        => 'book',
-				'status'      => array( 'draft' ),
-				'author_slug' => get_userdata( self::$user_ids['author_secondary'] )->user_nicename,
-			),
-			'fields' => array( 'id' ),
-		);
-
-		$this->login_as( 'editor' );
-		$hidden = $execute( $input );
-
-		$this->assertWPError( $hidden, 'An editor, who can edit others\' posts but not others\' books, should not learn that an author without published posts exists.' );
-		$this->assertSame( 'content_invalid_filter', $hidden->get_error_code(), 'An author hidden from the editor should be reported like a missing one.' );
-
-		wp_set_current_user( $this->create_subscriber_with_capabilities( array( 'edit_books', 'edit_others_books' ) ) );
-		$drafts = $execute( $input );
-
-		$this->assertIsArray( $drafts, 'A user who can edit others\' books should filter by an author without published posts.' );
-		$this->assertSame( array( $draft_id ), wp_list_pluck( $drafts['items'], 'id' ), 'The filter should return that author\'s draft books.' );
-	}
-
-	/**
-	 * On multisite, an author_slug filter does not tell an editor of one site whether a user
-	 * of another site exists.
+	 * On multisite, an author_slug filter that names a user of another site matches no post,
+	 * like a slug that names no user.
 	 *
 	 * @ticket 66268
 	 * @group ms-required
 	 * @since 7.2.0
 	 */
-	public function test_author_slug_filter_hides_users_of_other_sites(): void {
+	public function test_author_slug_filter_matches_no_post_for_a_user_of_another_site(): void {
 		$other_user_id = self::factory()->user->create( array( 'user_nicename' => 'other-site-user' ) );
 		$site_id       = self::factory()->blog->create();
 
@@ -5790,9 +5747,8 @@ public function test_author_slug_filter_hides_users_of_other_sites(): void {
 		restore_current_blog();
 
 		$this->assertFalse( $is_member, 'Precondition: the other user should not be a member of the site.' );
-		$this->assertWPError( $missing, 'Precondition: a slug that names no user should be rejected.' );
-		$this->assertWPError( $other, 'An editor should not learn that a user of another site exists.' );
-		$this->assertSame( $missing->get_error_code(), $other->get_error_code(), 'A user of another site should be reported like a missing one.' );
+		$this->assertSame( self::EMPTY_RESULT, $missing, 'Precondition: a slug that names no user should match no post.' );
+		$this->assertSame( self::EMPTY_RESULT, $other, 'A user of another site should match no post of the site.' );
 	}
 
 	/**