diff --git a/inc/functions/assets.php b/inc/functions/assets.php
index 4723302d..7ac8c477 100644
--- a/inc/functions/assets.php
+++ b/inc/functions/assets.php
@@ -29,21 +29,33 @@ function wu_get_asset($asset, $assets_dir = 'img', $base_dir = 'assets') {
 }
 
 /**
- * Checks if the current admin page belongs to WP Ultimo.
+ * Checks if the current admin page belongs to Ultimate Multisite.
  *
- * Used to guard asset enqueues so that WP Ultimo scripts and styles are only
- * loaded on WP Ultimo admin pages, not on every page in the network admin.
+ * Used to guard asset enqueues so that Ultimate Multisite scripts and styles are
+ * only loaded on Ultimate Multisite admin pages, not on every page in the network
+ * admin.
  *
- * Detection relies on the hook suffix passed to `admin_enqueue_scripts`. All
- * WP Ultimo admin pages register with an ID prefixed by `wp-ultimo`, which
- * WordPress uses when generating the page hook (e.g., `toplevel_page_wp-ultimo`,
- * `wp-ultimo_page_wp-ultimo-settings`). The hook suffix always contains the
- * page slug, so checking for `wp-ultimo` is reliable.
+ * Detection relies on the hook suffix passed to `admin_enqueue_scripts`. Core
+ * Ultimate Multisite admin pages register with an ID prefixed by `wp-ultimo`,
+ * which WordPress embeds in the generated page hook (e.g.,
+ * `toplevel_page_wp-ultimo`, `wp-ultimo_page_wp-ultimo-settings`). Addon pages
+ * typically register with an ID prefixed by `wu-` (e.g., `wu-networks`,
+ * `wu-sites-by-user`), and may appear either as top-level pages
+ * (`toplevel_page_wu-foo`) or as submenus of other menus (`*_page_wu-foo`).
+ *
+ * Recognized patterns:
+ * - Hook suffix contains `wp-ultimo` — core plugin pages and submenus.
+ * - Hook suffix contains `_page_wu-` — any page with a slug starting `wu-`
+ *   (covers `toplevel_page_wu-*` and `{parent}_page_wu-*`).
+ *
+ * The result is passed through the `wu_is_wu_page` filter so addons can
+ * explicitly register their pages when they use a non-standard slug.
  *
  * @since 2.4.2
+ * @since 2.6.3 Recognize pages with `wu-` slug prefix and add `wu_is_wu_page` filter.
  *
  * @param string $hook_suffix The hook suffix passed to `admin_enqueue_scripts`.
- * @return bool True if the current page is a WP Ultimo admin page.
+ * @return bool True if the current page is an Ultimate Multisite admin page.
  */
 function wu_is_wu_page(string $hook_suffix = ''): bool {
 
@@ -52,5 +64,30 @@ function wu_is_wu_page(string $hook_suffix = ''): bool {
 		$hook_suffix = $screen ? (string) $screen->id : '';
 	}
 
-	return str_contains($hook_suffix, 'wp-ultimo');
+	$is_wu_page = str_contains($hook_suffix, 'wp-ultimo')
+		|| str_contains($hook_suffix, '_page_wu-');
+
+	/**
+	 * Filters whether the current admin page is considered an Ultimate Multisite page.
+	 *
+	 * Addons that register admin pages with non-standard slugs (i.e., slugs that
+	 * do not contain `wp-ultimo` and do not start with `wu-`) should hook into
+	 * this filter to ensure the default Ultimate Multisite admin styles and
+	 * scripts (including wu-form modal styling) are enqueued on their pages.
+	 *
+	 * Example:
+	 *
+	 *     add_filter( 'wu_is_wu_page', function ( $is_wu_page, $hook_suffix ) {
+	 *         if ( str_contains( $hook_suffix, 'my-addon-slug' ) ) {
+	 *             return true;
+	 *         }
+	 *         return $is_wu_page;
+	 *     }, 10, 2 );
+	 *
+	 * @since 2.6.3
+	 *
+	 * @param bool   $is_wu_page  Whether the page is recognized as an Ultimate Multisite page.
+	 * @param string $hook_suffix The hook suffix for the current admin page.
+	 */
+	return (bool) apply_filters('wu_is_wu_page', $is_wu_page, $hook_suffix);
 }
diff --git a/tests/WP_Ultimo/Functions/Assets_Functions_Test.php b/tests/WP_Ultimo/Functions/Assets_Functions_Test.php
index 17956b3a..5c5035d4 100644
--- a/tests/WP_Ultimo/Functions/Assets_Functions_Test.php
+++ b/tests/WP_Ultimo/Functions/Assets_Functions_Test.php
@@ -67,4 +67,107 @@ public function test_wu_get_asset_custom_base_dir(): void {
 
 		$this->assertStringContainsString('static/img/', $result);
 	}
+
+	/**
+	 * Core top-level page hook.
+	 */
+	public function test_wu_is_wu_page_matches_core_toplevel(): void {
+
+		$this->assertTrue(wu_is_wu_page('toplevel_page_wp-ultimo'));
+	}
+
+	/**
+	 * Core submenu page hook.
+	 */
+	public function test_wu_is_wu_page_matches_core_submenu(): void {
+
+		$this->assertTrue(wu_is_wu_page('wp-ultimo_page_wp-ultimo-settings'));
+	}
+
+	/**
+	 * Addon page with wu- slug prefix registered as top-level (regression for #706).
+	 *
+	 * When the multinetwork addon adds its `wu-networks` page at top level,
+	 * the hook suffix does not contain `wp-ultimo`. It must still be recognized
+	 * so wu-admin.css / wu-admin.js are enqueued, otherwise wu-form modals
+	 * on that page render un-styled.
+	 */
+	public function test_wu_is_wu_page_matches_addon_toplevel_wu_slug(): void {
+
+		$this->assertTrue(wu_is_wu_page('toplevel_page_wu-networks'));
+	}
+
+	/**
+	 * Addon page with wu- slug prefix registered as network admin submenu.
+	 */
+	public function test_wu_is_wu_page_matches_addon_network_wu_slug(): void {
+
+		$this->assertTrue(wu_is_wu_page('toplevel_page_wu-networks-network'));
+	}
+
+	/**
+	 * Addon page submenu of a non-wu parent with wu- slug.
+	 */
+	public function test_wu_is_wu_page_matches_addon_submenu_wu_slug(): void {
+
+		$this->assertTrue(wu_is_wu_page('settings_page_wu-custom-addon'));
+	}
+
+	/**
+	 * Unrelated WordPress pages must not match.
+	 */
+	public function test_wu_is_wu_page_rejects_unrelated_pages(): void {
+
+		$this->assertFalse(wu_is_wu_page('edit-post'));
+		$this->assertFalse(wu_is_wu_page('options-general'));
+		$this->assertFalse(wu_is_wu_page('plugins'));
+		$this->assertFalse(wu_is_wu_page('toplevel_page_other-plugin'));
+	}
+
+	/**
+	 * A page slug that merely starts with `wu` (no hyphen) must not match, to
+	 * avoid false positives on slugs like `wunderground`.
+	 */
+	public function test_wu_is_wu_page_requires_hyphen_after_wu(): void {
+
+		$this->assertFalse(wu_is_wu_page('toplevel_page_wunderground'));
+	}
+
+	/**
+	 * The wu_is_wu_page filter allows addons with non-standard slugs to opt in.
+	 */
+	public function test_wu_is_wu_page_filter_opt_in(): void {
+
+		$callback = function ($is_wu_page, $hook_suffix) {
+			if ('toplevel_page_my-custom-addon' === $hook_suffix) {
+				return true;
+			}
+			return $is_wu_page;
+		};
+
+		add_filter('wu_is_wu_page', $callback, 10, 2);
+
+		$this->assertTrue(wu_is_wu_page('toplevel_page_my-custom-addon'));
+
+		remove_filter('wu_is_wu_page', $callback, 10);
+	}
+
+	/**
+	 * The wu_is_wu_page filter allows opting out of a core match.
+	 */
+	public function test_wu_is_wu_page_filter_opt_out(): void {
+
+		$callback = function ($is_wu_page, $hook_suffix) {
+			if ('toplevel_page_wp-ultimo' === $hook_suffix) {
+				return false;
+			}
+			return $is_wu_page;
+		};
+
+		add_filter('wu_is_wu_page', $callback, 10, 2);
+
+		$this->assertFalse(wu_is_wu_page('toplevel_page_wp-ultimo'));
+
+		remove_filter('wu_is_wu_page', $callback, 10);
+	}
 }
diff --git a/tests/WP_Ultimo/Scripts_Test.php b/tests/WP_Ultimo/Scripts_Test.php
index f437c807..3063467d 100644
--- a/tests/WP_Ultimo/Scripts_Test.php
+++ b/tests/WP_Ultimo/Scripts_Test.php
@@ -250,8 +250,8 @@ public function test_init_registers_hooks(): void {
 
 		$this->assertNotFalse(has_action('init', [$this->scripts, 'register_default_scripts']));
 		$this->assertNotFalse(has_action('init', [$this->scripts, 'register_default_styles']));
-		$this->assertNotFalse(has_action('admin_init', [$this->scripts, 'enqueue_default_admin_styles']));
-		$this->assertNotFalse(has_action('admin_init', [$this->scripts, 'enqueue_default_admin_scripts']));
+		$this->assertNotFalse(has_action('admin_enqueue_scripts', [$this->scripts, 'enqueue_default_admin_styles']));
+		$this->assertNotFalse(has_action('admin_enqueue_scripts', [$this->scripts, 'enqueue_default_admin_scripts']));
 		$this->assertNotFalse(has_filter('admin_body_class', [$this->scripts, 'add_body_class_container_boxed']));
 	}