diff --git a/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/php/full.php b/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/php/full.php
index 9e7b500795ec6..f87af5a1baba4 100644
--- a/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/php/full.php
+++ b/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/php/full.php
@@ -11,7 +11,6 @@
         'bad' => ['key' => 'foo'],
     ],
     'auto_reload' => true,
-    'base_template_class' => 'stdClass',
     'cache' => '/tmp',
     'charset' => 'ISO-8859-1',
     'debug' => true,
diff --git a/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/php/templateClass.php b/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/php/templateClass.php
new file mode 100644
index 0000000000000..bf995046314fa
--- /dev/null
+++ b/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/php/templateClass.php
@@ -0,0 +1,5 @@
+<?php
+
+$container->loadFromExtension('twig', [
+    'base_template_class' => 'stdClass',
+]);
diff --git a/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/xml/extra.xml b/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/xml/extra.xml
index 92767e411057f..f1cf8985329d0 100644
--- a/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/xml/extra.xml
+++ b/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/xml/extra.xml
@@ -6,7 +6,7 @@
     xsi:schemaLocation="http://symfony.com/schema/dic/services https://symfony.com/schema/dic/services/services-1.0.xsd
                         http://symfony.com/schema/dic/twig https://symfony.com/schema/dic/twig/twig-1.0.xsd">
 
-    <twig:config auto-reload="true" base-template-class="stdClass" cache="/tmp" charset="ISO-8859-1" debug="true" strict-variables="true">
+    <twig:config auto-reload="true" cache="/tmp" charset="ISO-8859-1" debug="true" strict-variables="true">
         <twig:path namespace="namespace3">namespaced_path3</twig:path>
     </twig:config>
 </container>
diff --git a/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/xml/full.xml b/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/xml/full.xml
index 3f7d1de266ec5..528a466b0452c 100644
--- a/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/xml/full.xml
+++ b/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/xml/full.xml
@@ -6,7 +6,7 @@
     xsi:schemaLocation="http://symfony.com/schema/dic/services https://symfony.com/schema/dic/services/services-1.0.xsd
                         http://symfony.com/schema/dic/twig https://symfony.com/schema/dic/twig/twig-1.0.xsd">
 
-    <twig:config auto-reload="true" base-template-class="stdClass" cache="/tmp" charset="ISO-8859-1" debug="true" strict-variables="true" default-path="%kernel.project_dir%/Fixtures/templates">
+    <twig:config auto-reload="true" cache="/tmp" charset="ISO-8859-1" debug="true" strict-variables="true" default-path="%kernel.project_dir%/Fixtures/templates">
         <twig:form-theme>MyBundle::form.html.twig</twig:form-theme>
         <twig:global key="foo" id="bar" type="service" />
         <twig:global key="baz">@@qux</twig:global>
diff --git a/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/xml/templateClass.xml b/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/xml/templateClass.xml
new file mode 100644
index 0000000000000..a735ed8da258e
--- /dev/null
+++ b/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/xml/templateClass.xml
@@ -0,0 +1,10 @@
+<?xml version="1.0" ?>
+
+<container xmlns="http://symfony.com/schema/dic/services"
+           xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
+           xmlns:twig="http://symfony.com/schema/dic/twig"
+           xsi:schemaLocation="http://symfony.com/schema/dic/services https://symfony.com/schema/dic/services/services-1.0.xsd
+                        http://symfony.com/schema/dic/twig https://symfony.com/schema/dic/twig/twig-1.0.xsd">
+
+    <twig:config base-template-class="stdClass" />
+</container>
diff --git a/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/yml/full.yml b/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/yml/full.yml
index d186724539927..6c249d378ff22 100644
--- a/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/yml/full.yml
+++ b/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/yml/full.yml
@@ -7,7 +7,6 @@ twig:
         pi:  3.14
         bad: {key: foo}
     auto_reload:         true
-    base_template_class: stdClass
     cache:               /tmp
     charset:             ISO-8859-1
     debug:               true
diff --git a/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/yml/templateClass.yml b/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/yml/templateClass.yml
new file mode 100644
index 0000000000000..886a5ee60d9a5
--- /dev/null
+++ b/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/Fixtures/yml/templateClass.yml
@@ -0,0 +1,2 @@
+twig:
+    base_template_class: stdClass
diff --git a/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/TwigExtensionTest.php b/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/TwigExtensionTest.php
index 7a874e7bab8bc..bc7013c3cb70a 100644
--- a/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/TwigExtensionTest.php
+++ b/src/Symfony/Bundle/TwigBundle/Tests/DependencyInjection/TwigExtensionTest.php
@@ -11,6 +11,7 @@
 
 namespace Symfony\Bundle\TwigBundle\Tests\DependencyInjection;
 
+use Symfony\Bridge\PhpUnit\ExpectDeprecationTrait;
 use Symfony\Bundle\TwigBundle\DependencyInjection\Compiler\RuntimeLoaderPass;
 use Symfony\Bundle\TwigBundle\DependencyInjection\TwigExtension;
 use Symfony\Bundle\TwigBundle\Tests\DependencyInjection\AcmeBundle\AcmeBundle;
@@ -31,6 +32,8 @@
 
 class TwigExtensionTest extends TestCase
 {
+    use ExpectDeprecationTrait;
+
     public function testLoadEmptyConfiguration()
     {
         $container = $this->createContainer();
@@ -56,7 +59,7 @@ public function testLoadEmptyConfiguration()
     /**
      * @dataProvider getFormats
      */
-    public function testLoadFullConfiguration($format)
+    public function testLoadFullConfiguration(string $format)
     {
         $container = $this->createContainer();
         $container->registerExtension(new TwigExtension());
@@ -91,17 +94,36 @@ public function testLoadFullConfiguration($format)
         $options = $container->getDefinition('twig')->getArgument(1);
         $this->assertTrue($options['auto_reload'], '->load() sets the auto_reload option');
         $this->assertSame('name', $options['autoescape'], '->load() sets the autoescape option');
-        $this->assertEquals('stdClass', $options['base_template_class'], '->load() sets the base_template_class option');
+        $this->assertArrayNotHasKey('base_template_class', $options, '->load() does not set the base_template_class if none is provided');
         $this->assertEquals('/tmp', $options['cache'], '->load() sets the cache option');
         $this->assertEquals('ISO-8859-1', $options['charset'], '->load() sets the charset option');
         $this->assertTrue($options['debug'], '->load() sets the debug option');
         $this->assertTrue($options['strict_variables'], '->load() sets the strict_variables option');
     }
 
+    /**
+     * @group legacy
+     *
+     * @dataProvider getFormats
+     */
+    public function testLoadCustomBaseTemplateClassConfiguration(string $format)
+    {
+        $container = $this->createContainer();
+        $container->registerExtension(new TwigExtension());
+
+        $this->expectDeprecation('Since symfony/twig-bundle 7.1: The child node "base_template_class" at path "twig" is deprecated.');
+
+        $this->loadFromFile($container, 'templateClass', $format);
+        $this->compileContainer($container);
+
+        $options = $container->getDefinition('twig')->getArgument(1);
+        $this->assertEquals('stdClass', $options['base_template_class'], '->load() sets the base_template_class option');
+    }
+
     /**
      * @dataProvider getFormats
      */
-    public function testLoadCustomTemplateEscapingGuesserConfiguration($format)
+    public function testLoadCustomTemplateEscapingGuesserConfiguration(string $format)
     {
         $container = $this->createContainer();
         $container->registerExtension(new TwigExtension());
@@ -115,7 +137,7 @@ public function testLoadCustomTemplateEscapingGuesserConfiguration($format)
     /**
      * @dataProvider getFormats
      */
-    public function testLoadDefaultTemplateEscapingGuesserConfiguration($format)
+    public function testLoadDefaultTemplateEscapingGuesserConfiguration(string $format)
     {
         $container = $this->createContainer();
         $container->registerExtension(new TwigExtension());
@@ -129,7 +151,7 @@ public function testLoadDefaultTemplateEscapingGuesserConfiguration($format)
     /**
      * @dataProvider getFormats
      */
-    public function testLoadCustomDateFormats($fileFormat)
+    public function testLoadCustomDateFormats(string $fileFormat)
     {
         $container = $this->createContainer();
         $container->registerExtension(new TwigExtension());
@@ -178,7 +200,7 @@ public function testGlobalsWithDifferentTypesAndValues()
     /**
      * @dataProvider getFormats
      */
-    public function testTwigLoaderPaths($format)
+    public function testTwigLoaderPaths(string $format)
     {
         $container = $this->createContainer();
         $container->registerExtension(new TwigExtension());
@@ -207,7 +229,7 @@ public function testTwigLoaderPaths($format)
         ], $paths);
     }
 
-    public static function getFormats()
+    public static function getFormats(): array
     {
         return [
             ['php'],
@@ -219,7 +241,7 @@ public static function getFormats()
     /**
      * @dataProvider stopwatchExtensionAvailabilityProvider
      */
-    public function testStopwatchExtensionAvailability($debug, $stopwatchEnabled, $expected)
+    public function testStopwatchExtensionAvailability(bool $debug, bool $stopwatchEnabled, bool $expected)
     {
         $container = $this->createContainer();
         $container->setParameter('kernel.debug', $debug);
@@ -290,7 +312,7 @@ public function testCustomHtmlToTextConverterService(string $format)
         $this->assertEquals(new Reference('my_converter'), $bodyRenderer->getArgument('$converter'));
     }
 
-    private function createContainer()
+    private function createContainer(): ContainerBuilder
     {
         $container = new ContainerBuilder(new ParameterBag([
             'kernel.cache_dir' => __DIR__,
@@ -311,7 +333,7 @@ private function createContainer()
         return $container;
     }
 
-    private function compileContainer(ContainerBuilder $container)
+    private function compileContainer(ContainerBuilder $container): void
     {
         $container->getCompilerPassConfig()->setOptimizationPasses([]);
         $container->getCompilerPassConfig()->setRemovingPasses([]);
@@ -319,7 +341,7 @@ private function compileContainer(ContainerBuilder $container)
         $container->compile();
     }
 
-    private function loadFromFile(ContainerBuilder $container, $file, $format)
+    private function loadFromFile(ContainerBuilder $container, string $file, string $format): void
     {
         $locator = new FileLocator(__DIR__.'/Fixtures/'.$format);