diff --git a/doc/advanced.rst b/doc/advanced.rst
index 17e2c7fd426..e88a8f73907 100644
--- a/doc/advanced.rst
+++ b/doc/advanced.rst
@@ -761,13 +761,12 @@ Using PHP Attributes to define extensions
 
 .. versionadded:: 3.9
 
-    The ``Twig\Extension\AttributeExtension`` was added in Twig 3.9.
+    The attribute classes were added in Twig 3.9.
 
 From PHP 8.0, you can use the attributes ``#[AsTwigFilter]``, ``#[AsTwigFunction]``,
 and ``#[AsTwigTest]`` on any method of any class to define filters, functions, and tests.
 
-Create a class, you don't need to extend any class or implement any interface
-but it eases integration with frameworks if you use the attribute ``#[AsTwigExtension]``::
+Create a class with the attribute ``#[AsTwigExtension]``::
 
     use Twig\Attribute\AsTwigExtension;
     use Twig\Attribute\AsTwigFilter;
@@ -775,7 +774,7 @@ but it eases integration with frameworks if you use the attribute ``#[AsTwigExte
     use Twig\Attribute\AsTwigTest;
 
     #[AsTwigExtension]
-    class Project_Twig_Extension
+    class ProjectExtension
     {
         #[AsTwigFilter('rot13')]
         public static function rot13(string $string): string
@@ -796,16 +795,10 @@ but it eases integration with frameworks if you use the attribute ``#[AsTwigExte
         }
     }
 
-Then register the class using ``Twig\Extension\AttributeExtension``::
+Then register the extension class::
 
     $twig = new \Twig\Environment($loader);
-    $twig->addExtension(new \Twig\Extension\AttributeExtension([
-        Project_Twig_Extension::class,
-    ]));
-
-.. note::
-
-    The ``\Twig\Extension\AttributeExtension`` can be added only once to an environment.
+    $twig->addExtension(ProjectExtension::class);
 
 If all the methods are static, you are done. The ``Project_Twig_Extension`` class will
 never be instantiated and the class attributes will be scanned only when a template
@@ -818,7 +811,7 @@ a runtime extension using one of the runtime loaders::
     use Twig\Attribute\AsTwigFunction;
 
     #[AsTwigExtension]
-    class Project_Service
+    class ProjectExtension
     {
         // Inject hypothetical dependencies
         public function __construct(private LipsumProvider $lipsumProvider) {}
@@ -831,21 +824,17 @@ a runtime extension using one of the runtime loaders::
     }
 
     $twig = new \Twig\Environment($loader);
-    $twig->addExtension(new \Twig\Extension\AttributeExtension([
-        Project_Twig_Extension::class,
-    ]));
+    $twig->addExtension(ProjectExtension::class);
     $twig->addRuntimeLoader(new \Twig\RuntimeLoader\FactoryLoader([
-        Project_Twig_Extension::class => function () use ($lipsumProvider) {
-            return new Project_Twig_Extension($lipsumProvider);
+        ProjectExtension::class => function () use ($lipsumProvider) {
+            return new ProjectExtension($lipsumProvider);
         },
     ]));
 
 Or use the instance directly if you don't need lazy-loading::
 
     $twig = new \Twig\Environment($loader);
-    $twig->addExtension(new \Twig\Extension\AttributeExtension([
-        new Project_Twig_Extension($lipsumProvider),
-    ]));
+    $twig->addExtension(new ProjectExtension($lipsumProvider));
 
 ``#[AsTwigFilter]`` and ``#[AsTwigFunction]`` support ``isSafe``, ``preEscape``, and
 ``isVariadic`` options::
@@ -855,7 +844,7 @@ Or use the instance directly if you don't need lazy-loading::
     use Twig\Attribute\AsTwigFunction;
 
     #[AsTwigExtension]
-    class Project_Twig_Extension
+    class ProjectExtension
     {
         #[AsTwigFilter('rot13', isSafe: ['html'])]
         public static function rot13(string $string): string
@@ -873,7 +862,7 @@ Or use the instance directly if you don't need lazy-loading::
 If you want to access the current environment instance in your filter or function,
 add the ``Twig\Environment`` type to the first argument of the method::
 
-    class Project_Twig_Extension
+    class ProjectExtension
     {
         #[AsTwigFunction('lipsum')]
         public function lipsum(\Twig\Environment $env, int $count): string
@@ -885,7 +874,7 @@ add the ``Twig\Environment`` type to the first argument of the method::
 If you want to access the current context in your filter or function, add an argument
 with type and name ``array $context`` first or after ``\Twig\Environment``::
 
-    class Project_Twig_Extension
+    class ProjectExtension
     {
         #[AsTwigFunction('lipsum')]
         public function lipsum(array $context, int $count): string
@@ -897,7 +886,7 @@ with type and name ``array $context`` first or after ``\Twig\Environment``::
 ``#[AsTwigFilter]`` and ``#[AsTwigFunction]`` support variadic arguments
 automatically when applied to variadic methods::
 
-    class Project_Twig_Extension
+    class ProjectExtension
     {
         #[AsTwigFilter('thumbnail')]
         public function thumbnail(string $file, mixed ...$options): string
diff --git a/src/Environment.php b/src/Environment.php
index ec9c39da5ac..5d350bc5179 100644
--- a/src/Environment.php
+++ b/src/Environment.php
@@ -616,14 +616,17 @@ public function getRuntime(string $class)
         throw new RuntimeError(sprintf('Unable to load the "%s" runtime.', $class));
     }
 
-    public function addExtension(ExtensionInterface $extension)
+    /**
+     * @param ExtensionInterface|object|class-string $extension
+     */
+    public function addExtension(object|string $extension)
     {
         $this->extensionSet->addExtension($extension);
         $this->updateOptionsHash();
     }
 
     /**
-     * @param ExtensionInterface[] $extensions An array of extensions
+     * @param list<ExtensionInterface|object|class-string> $extensions An array of extensions
      */
     public function setExtensions(array $extensions)
     {
diff --git a/src/Extension/AttributeExtension.php b/src/Extension/AttributeExtension.php
index 1fc64b69eb7..c2ec849b464 100644
--- a/src/Extension/AttributeExtension.php
+++ b/src/Extension/AttributeExtension.php
@@ -11,6 +11,7 @@
 
 namespace Twig\Extension;
 
+use Twig\Attribute\AsTwigExtension;
 use Twig\Attribute\AsTwigFilter;
 use Twig\Attribute\AsTwigFunction;
 use Twig\Attribute\AsTwigTest;
@@ -23,36 +24,25 @@
  * Define Twig filters, functions, and tests with PHP attributes.
  *
  * @author Jérôme Tamarelle <jerome@tamarelle.net>
+ *
+ * @internal
  */
-final class AttributeExtension extends AbstractExtension implements ModificationAwareInterface
+final class AttributeExtension extends AbstractExtension
 {
+    private array $classes;
     private array $filters;
     private array $functions;
     private array $tests;
 
-    public function __construct(
-        /**
-         * A list of objects or class names defining filters, functions, and tests using PHP attributes.
-         * When passing a class name, it must be available in runtimes.
-         *
-         * @var iterable<object|class-string>
-         */
-        private iterable $objectsOrClasses,
-    ) {
-    }
-
-    public function getLastModified(): int
+    /**
+     * A list of objects or class names defining filters, functions, and tests using PHP attributes.
+     * When passing a class name, it must be available in runtimes.
+     *
+     * @param class-string[]
+     */
+    public function __construct(array $classes)
     {
-        $lastModified = 0;
-
-        foreach ($this->objectsOrClasses as $objectOrClass) {
-            $r = new \ReflectionClass($objectOrClass);
-            if (is_file($r->getFileName()) && $lastModified < $extensionTime = filemtime($r->getFileName())) {
-                $lastModified = $extensionTime;
-            }
-        }
-
-        return $lastModified;
+        $this->classes = $classes;
     }
 
     public function getFilters(): array
@@ -86,13 +76,18 @@ private function initFromAttributes()
     {
         $filters = $functions = $tests = [];
 
-        foreach ($this->objectsOrClasses as $objectOrClass) {
+        foreach ($this->classes as $objectOrClass) {
             try {
                 $reflectionClass = new \ReflectionClass($objectOrClass);
             } catch (\ReflectionException $e) {
                 throw new \LogicException(sprintf('"%s" class requires a list of objects or class name, "%s" given.', __CLASS__, get_debug_type($objectOrClass)), 0, $e);
             }
 
+            $attributes = $reflectionClass->getAttributes(AsTwigExtension::class);
+            if (!$attributes) {
+                throw new \LogicException(sprintf('Extension class "%s" must have the attribute "%s" in order to use attributes', is_string($objectOrClass) ? $objectOrClass : get_debug_type($objectOrClass), AsTwigExtension::class));
+            }
+
             foreach ($reflectionClass->getMethods() as $method) {
                 // Filters
                 foreach ($method->getAttributes(AsTwigFilter::class) as $attribute) {
diff --git a/src/Extension/ModificationAwareInterface.php b/src/Extension/ModificationAwareInterface.php
deleted file mode 100644
index e85c3ca4ed0..00000000000
--- a/src/Extension/ModificationAwareInterface.php
+++ /dev/null
@@ -1,15 +0,0 @@
-<?php
-
-namespace Twig\Extension;
-
-/**
- * Freshness of templates use the last modification date of each extension class.
- * Implement this interface to provide a different modification date for the extension.
- */
-interface ModificationAwareInterface
-{
-    /**
-     * @return int A UNIX timestamp
-     */
-    public function getLastModified(): int;
-}
diff --git a/src/ExtensionSet.php b/src/ExtensionSet.php
index d77d86e3e18..f2a8cd247c2 100644
--- a/src/ExtensionSet.php
+++ b/src/ExtensionSet.php
@@ -12,6 +12,7 @@
 namespace Twig;
 
 use Twig\Error\RuntimeError;
+use Twig\Extension\AttributeExtension;
 use Twig\Extension\ExtensionInterface;
 use Twig\Extension\GlobalsInterface;
 use Twig\Extension\StagingExtension;
@@ -74,11 +75,15 @@ public function getExtension(string $class): ExtensionInterface
             throw new RuntimeError(sprintf('The "%s" extension is not enabled.', $class));
         }
 
+        if (is_string($this->extensions[$class])) {
+            throw new RuntimeError(sprintf('The "%s" uses attributes, it requires a runtime.', $class));
+        }
+
         return $this->extensions[$class];
     }
 
     /**
-     * @param ExtensionInterface[] $extensions
+     * @param list<ExtensionInterface|class-string> $extensions
      */
     public function setExtensions(array $extensions): void
     {
@@ -112,11 +117,8 @@ public function getLastModified(): int
         }
 
         foreach ($this->extensions as $extension) {
-            $r = new \ReflectionObject($extension);
-            if (is_file($r->getFileName()) && $this->lastModified < $extensionTime = filemtime($r->getFileName())) {
-                $this->lastModified = $extensionTime;
-            }
-            if ($extension instanceof ModificationAwareInterface && $this->lastModified < $extensionTime = $extension->getLastModified()) {
+            $r = new \ReflectionClass($extension);
+            if (($filename = $r->getFileName()) && is_file($filename) && $this->lastModified < $extensionTime = filemtime($filename)) {
                 $this->lastModified = $extensionTime;
             }
         }
@@ -124,9 +126,12 @@ public function getLastModified(): int
         return $this->lastModified;
     }
 
-    public function addExtension(ExtensionInterface $extension): void
+    /**
+     * @param ExtensionInterface|class-string|object $extension
+     */
+    public function addExtension(string|object $extension): void
     {
-        $class = \get_class($extension);
+        $class = is_string($extension) ? $extension : \get_class($extension);
 
         if ($this->initialized) {
             throw new \LogicException(sprintf('Unable to register extension "%s" as extensions have already been initialized.', $class));
@@ -428,9 +433,16 @@ private function initExtensions(): void
         $this->unaryOperators = [];
         $this->binaryOperators = [];
 
+        $classes = [];
         foreach ($this->extensions as $extension) {
-            $this->initExtension($extension);
+            if ($extension instanceof ExtensionInterface) {
+                $this->initExtension($extension);
+            } else {
+                $classes[] = $extension;
+            }
         }
+
+        $this->initExtension(new AttributeExtension($classes));
         $this->initExtension($this->staging);
         // Done at the end only, so that an exception during initialization does not mark the environment as initialized when catching the exception
         $this->initialized = true;
diff --git a/tests/Extension/AttributeExtensionTest.php b/tests/Extension/AttributeExtensionTest.php
index e62f15c04b4..14244fbf8e0 100644
--- a/tests/Extension/AttributeExtensionTest.php
+++ b/tests/Extension/AttributeExtensionTest.php
@@ -107,10 +107,4 @@ public function testRuntimeExtension()
         $this->assertSame([$class, 'fooFunction'], $extension->getFunctions()['foo']->getCallable());
         $this->assertSame([$class, 'fooTest'], $extension->getTests()['foo']->getCallable());
     }
-
-    public function testLastModified()
-    {
-        $extension = new AttributeExtension([ExtensionWithAttributes::class]);
-        $this->assertSame(filemtime(__DIR__.'/Fixtures/ExtensionWithAttributes.php'), $extension->getLastModified());
-    }
 }