diff --git a/src/Sites/Site.php b/src/Sites/Site.php
index 7f0b4123fb8..430045940be 100644
--- a/src/Sites/Site.php
+++ b/src/Sites/Site.php
@@ -119,6 +119,10 @@ protected function resolveAntlersValue($value)
                 ->all();
         }
 
+        if (! is_string($value) || ! Str::contains($value, ['{', '@'])) {
+            return $value;
+        }
+
         $value = Parse::config($value);
 
         $isEvaluatingUserData = GlobalRuntimeState::$isEvaluatingUserData;
diff --git a/src/Sites/Sites.php b/src/Sites/Sites.php
index aaec4b29c24..d00c0cd65e8 100644
--- a/src/Sites/Sites.php
+++ b/src/Sites/Sites.php
@@ -39,6 +39,10 @@ public function all()
 
     public function authorized()
     {
+        if (User::current()->isSuper()) {
+            return $this->sites;
+        }
+
         return $this->sites->filter(fn ($site) => User::current()->can('view', $site));
     }
 
diff --git a/src/Structures/Nav.php b/src/Structures/Nav.php
index ce901447c03..dc3a38c0e1b 100644
--- a/src/Structures/Nav.php
+++ b/src/Structures/Nav.php
@@ -145,7 +145,7 @@ public function sites()
 
     public function existsIn($site)
     {
-        return $this->trees()->has($site);
+        return $this->in($site) !== null;
     }
 
     public function blueprint()
diff --git a/tests/Performance/SitesPerformanceTest.php b/tests/Performance/SitesPerformanceTest.php
new file mode 100644
index 00000000000..d61c114c57d
--- /dev/null
+++ b/tests/Performance/SitesPerformanceTest.php
@@ -0,0 +1,115 @@
+<?php
+
+namespace Tests\Performance;
+
+use PHPUnit\Framework\Attributes\Test;
+use Statamic\Facades\Role;
+use Statamic\Facades\User;
+use Statamic\Sites\Site;
+use Statamic\Sites\Sites;
+use Tests\PreventSavingStacheItemsToDisk;
+use Tests\TestCase;
+
+class SitesPerformanceTest extends TestCase
+{
+    use PreventSavingStacheItemsToDisk;
+
+    /**
+     * Test that super users bypass authorization filtering for all sites.
+     * This ensures the performance optimization for super users is working.
+     */
+    #[Test]
+    public function super_user_bypasses_site_authorization_check()
+    {
+        $sites = (new Sites)->setSites([
+            'en' => ['url' => 'http://test.com/'],
+            'fr' => ['url' => 'http://fr.test.com/'],
+            'de' => ['url' => 'http://test.com/de/'],
+        ]);
+
+        // Create and act as a super user
+        $superUser = tap(User::make()->id(1))->save();
+        $superUser->makeSuper()->save();
+        $this->actingAs($superUser);
+
+        // Super user should get all sites without any filtering
+        $authorizedSites = $sites->authorized();
+
+        $this->assertEquals(3, $authorizedSites->count());
+        $this->assertEquals(['en', 'fr', 'de'], $authorizedSites->keys()->all());
+    }
+
+    /**
+     * Test that regular users still get filtered authorization check.
+     * This ensures regular users only see sites they have access to.
+     */
+    #[Test]
+    public function regular_user_gets_filtered_site_authorization()
+    {
+        $sites = (new Sites)->setSites([
+            'en' => ['url' => 'http://test.com/'],
+            'fr' => ['url' => 'http://fr.test.com/'],
+            'de' => ['url' => 'http://test.com/de/'],
+        ]);
+
+        Role::make('editor')
+            ->permissions([
+                'access en site',
+                'access fr site',
+            ])
+            ->save();
+
+        $regularUser = tap(User::make()->assignRole('editor'))->save();
+        $this->actingAs($regularUser);
+
+        \Statamic\Facades\Site::shouldReceive('multiEnabled')->andReturnTrue();
+        \Statamic\Facades\Site::shouldReceive('all')->andReturn(collect()); // CorePermissions calls this
+
+        // Regular user should only get sites they have access to
+        $authorizedSites = $sites->authorized();
+
+        $this->assertEquals(2, $authorizedSites->count());
+        $this->assertEquals(['en', 'fr'], $authorizedSites->keys()->all());
+    }
+
+    /**
+     * Test that site configuration with plain strings doesn't trigger Antlers parsing.
+     * This ensures performance optimization for non-template string values.
+     */
+    #[Test]
+    public function plain_string_site_config_skips_antlers_parsing()
+    {
+        // Test with a simple string URL that has no template syntax
+        $site = new Site('en', [
+            'url' => '/en/',
+            'locale' => 'en_US',
+            'name' => 'English',
+        ]);
+
+        // These should be plain strings, not parsed by Antlers
+        // Note: URLs are tidied, so trailing slash is removed
+        $this->assertEquals('/en', $site->url());
+        $this->assertEquals('en_US', $site->locale());
+        $this->assertEquals('English', $site->name());
+    }
+
+    /**
+     * Test that site configuration with Antlers syntax still gets parsed.
+     * This ensures the optimization doesn't break actual template parsing.
+     */
+    #[Test]
+    public function site_config_with_antlers_syntax_gets_parsed()
+    {
+        // Test with template syntax that should be parsed
+        $site = new Site('en', [
+            'url' => '/',
+            'locale' => '{{ config:app.locale }}',
+            'name' => 'Test Site',
+        ]);
+
+        // Locale should have been parsed
+        $this->assertNotEmpty($site->locale());
+        // It should not contain the template syntax anymore
+        $this->assertStringNotContainsString('{{', $site->locale());
+    }
+}
diff --git a/tests/Structures/NavPerformanceTest.php b/tests/Structures/NavPerformanceTest.php
new file mode 100644
index 00000000000..c3bc25b7d43
--- /dev/null
+++ b/tests/Structures/NavPerformanceTest.php
@@ -0,0 +1,73 @@
+<?php
+
+namespace Tests\Structures;
+
+use PHPUnit\Framework\Attributes\Test;
+use Statamic\Facades\Nav;
+use Tests\PreventSavingStacheItemsToDisk;
+use Tests\TestCase;
+use Tests\UnlinksPaths;
+
+class NavPerformanceTest extends TestCase
+{
+    use PreventSavingStacheItemsToDisk;
+    use UnlinksPaths;
+
+    private $directory;
+
+    public function setUp(): void
+    {
+        parent::setUp();
+
+        $stache = $this->app->make('stache');
+        $stache->store('nav-trees')->directory($this->directory = $this->fakeStacheDirectory.$this->directory.'');
+
+        $this->setSites([
+            'en' => ['locale' => 'en_US', 'url' => '/'],
+            'fr' => ['locale' => 'fr_FR', 'url' => '/fr/'],
+            'de' => ['locale' => 'de_DE', 'url' => '/de/'],
+        ]);
+    }
+
+    /**
+     * Test that existsIn() efficiently checks for nav in a specific site.
+     * This verifies the performance optimization that uses in() instead of trees().
+     */
+    #[Test]
+    public function exists_in_checks_nav_for_specific_site()
+    {
+        $nav = tap(Nav::make('links'))->save();
+
+        // Create a tree for only the 'en' site
+        $nav->makeTree('en', [['title' => 'Home', 'url' => '/']])->save();
+
+        // Nav should exist in 'en' site
+        $this->assertTrue($nav->existsIn('en'));
+
+        // Nav should not exist in 'fr' site
+        $this->assertFalse($nav->existsIn('fr'));
+
+        // Nav should not exist in 'de' site
+        $this->assertFalse($nav->existsIn('de'));
+    }
+
+    /**
+     * Test that existsIn() works when nav exists in multiple sites.
+     */
+    #[Test]
+    public function exists_in_checks_nav_across_multiple_sites()
+    {
+        $nav = tap(Nav::make('links'))->save();
+
+        // Create trees for 'en' and 'fr' sites
+        $nav->makeTree('en', [['title' => 'Home', 'url' => '/']])->save();
+        $nav->makeTree('fr', [['title' => 'Accueil', 'url' => '/']])->save();
+
+        // Nav should exist in both 'en' and 'fr' sites
+        $this->assertTrue($nav->existsIn('en'));
+        $this->assertTrue($nav->existsIn('fr'));
+
+        // Nav should not exist in 'de' site
+        $this->assertFalse($nav->existsIn('de'));
+    }
+}