diff --git a/src/Symfony/Component/DependencyInjection/CHANGELOG.md b/src/Symfony/Component/DependencyInjection/CHANGELOG.md
index 9413290cf615..afc87d925f30 100644
--- a/src/Symfony/Component/DependencyInjection/CHANGELOG.md
+++ b/src/Symfony/Component/DependencyInjection/CHANGELOG.md
@@ -10,6 +10,8 @@ CHANGELOG
  * Add `#[Lazy]` attribute as shortcut for `#[Autowire(lazy: [bool|string])]` and `#[Autoconfigure(lazy: [bool|string])]`
  * Add `#[AutowireMethodOf]` attribute to autowire a method of a service as a callable
  * Make `ContainerBuilder::registerAttributeForAutoconfiguration()` propagate to attribute classes that extend the registered class
+ * Add argument `$prepend` to `FileLoader::construct()` to prepend loaded configuration instead of appending it
+ * [BC BREAK] When used in the `prependExtension()` methods, the `ContainerConfigurator::import()` method now prepends the configuration instead of appending it
 
 7.0
 ---
diff --git a/src/Symfony/Component/DependencyInjection/Extension/AbstractExtension.php b/src/Symfony/Component/DependencyInjection/Extension/AbstractExtension.php
index c5c2f17adf97..795ed810dfc9 100644
--- a/src/Symfony/Component/DependencyInjection/Extension/AbstractExtension.php
+++ b/src/Symfony/Component/DependencyInjection/Extension/AbstractExtension.php
@@ -49,7 +49,7 @@ final public function prepend(ContainerBuilder $container): void
             $this->prependExtension($configurator, $container);
         };
 
-        $this->executeConfiguratorCallback($container, $callback, $this);
+        $this->executeConfiguratorCallback($container, $callback, $this, true);
     }
 
     final public function load(array $configs, ContainerBuilder $container): void
diff --git a/src/Symfony/Component/DependencyInjection/Extension/ExtensionTrait.php b/src/Symfony/Component/DependencyInjection/Extension/ExtensionTrait.php
index 5bd88892fb9b..0bb008860fe0 100644
--- a/src/Symfony/Component/DependencyInjection/Extension/ExtensionTrait.php
+++ b/src/Symfony/Component/DependencyInjection/Extension/ExtensionTrait.php
@@ -30,10 +30,10 @@
  */
 trait ExtensionTrait
 {
-    private function executeConfiguratorCallback(ContainerBuilder $container, \Closure $callback, ConfigurableExtensionInterface $subject): void
+    private function executeConfiguratorCallback(ContainerBuilder $container, \Closure $callback, ConfigurableExtensionInterface $subject, bool $prepend = false): void
     {
         $env = $container->getParameter('kernel.environment');
-        $loader = $this->createContainerLoader($container, $env);
+        $loader = $this->createContainerLoader($container, $env, $prepend);
         $file = (new \ReflectionObject($subject))->getFileName();
         $bundleLoader = $loader->getResolver()->resolve($file);
         if (!$bundleLoader instanceof PhpFileLoader) {
@@ -50,15 +50,15 @@ private function executeConfiguratorCallback(ContainerBuilder $container, \Closu
         }
     }
 
-    private function createContainerLoader(ContainerBuilder $container, string $env): DelegatingLoader
+    private function createContainerLoader(ContainerBuilder $container, string $env, bool $prepend): DelegatingLoader
     {
         $buildDir = $container->getParameter('kernel.build_dir');
         $locator = new FileLocator();
         $resolver = new LoaderResolver([
-            new XmlFileLoader($container, $locator, $env),
-            new YamlFileLoader($container, $locator, $env),
+            new XmlFileLoader($container, $locator, $env, $prepend),
+            new YamlFileLoader($container, $locator, $env, $prepend),
             new IniFileLoader($container, $locator, $env),
-            new PhpFileLoader($container, $locator, $env, new ConfigBuilderGenerator($buildDir)),
+            new PhpFileLoader($container, $locator, $env, new ConfigBuilderGenerator($buildDir), $prepend),
             new GlobFileLoader($container, $locator, $env),
             new DirectoryLoader($container, $locator, $env),
             new ClosureLoader($container, $env),
diff --git a/src/Symfony/Component/DependencyInjection/Loader/FileLoader.php b/src/Symfony/Component/DependencyInjection/Loader/FileLoader.php
index 76432ad36086..669082179675 100644
--- a/src/Symfony/Component/DependencyInjection/Loader/FileLoader.php
+++ b/src/Symfony/Component/DependencyInjection/Loader/FileLoader.php
@@ -45,10 +45,17 @@ abstract class FileLoader extends BaseFileLoader
     /** @var array<string, Alias> */
     protected array $aliases = [];
     protected bool $autoRegisterAliasesForSinglyImplementedInterfaces = true;
+    protected bool $prepend = false;
+    protected array $extensionConfigs = [];
+    protected int $importing = 0;
 
-    public function __construct(ContainerBuilder $container, FileLocatorInterface $locator, ?string $env = null)
+    /**
+     * @param bool $prepend Whether to prepend extension config instead of appending them
+     */
+    public function __construct(ContainerBuilder $container, FileLocatorInterface $locator, ?string $env = null, bool $prepend = false)
     {
         $this->container = $container;
+        $this->prepend = $prepend;
 
         parent::__construct($locator, $env);
     }
@@ -66,6 +73,7 @@ public function import(mixed $resource, ?string $type = null, bool|string $ignor
             throw new \TypeError(sprintf('Invalid argument $ignoreErrors provided to "%s::import()": boolean or "not_found" expected, "%s" given.', static::class, get_debug_type($ignoreErrors)));
         }
 
+        ++$this->importing;
         try {
             return parent::import(...$args);
         } catch (LoaderLoadException $e) {
@@ -82,6 +90,8 @@ public function import(mixed $resource, ?string $type = null, bool|string $ignor
             if (__FILE__ !== $frame['file']) {
                 throw $e;
             }
+        } finally {
+            --$this->importing;
         }
 
         return null;
@@ -217,6 +227,41 @@ public function registerAliasesForSinglyImplementedInterfaces(): void
         $this->interfaces = $this->singlyImplemented = $this->aliases = [];
     }
 
+    final protected function loadExtensionConfig(string $namespace, array $config): void
+    {
+        if (!$this->prepend) {
+            $this->container->loadFromExtension($namespace, $config);
+
+            return;
+        }
+
+        if ($this->importing) {
+            if (!isset($this->extensionConfigs[$namespace])) {
+                $this->extensionConfigs[$namespace] = [];
+            }
+            array_unshift($this->extensionConfigs[$namespace], $config);
+
+            return;
+        }
+
+        $this->container->prependExtensionConfig($namespace, $config);
+    }
+
+    final protected function loadExtensionConfigs(): void
+    {
+        if ($this->importing || !$this->extensionConfigs) {
+            return;
+        }
+
+        foreach ($this->extensionConfigs as $namespace => $configs) {
+            foreach ($configs as $config) {
+                $this->container->prependExtensionConfig($namespace, $config);
+            }
+        }
+
+        $this->extensionConfigs = [];
+    }
+
     /**
      * Registers a definition in the container with its instanceof-conditionals.
      */
diff --git a/src/Symfony/Component/DependencyInjection/Loader/PhpFileLoader.php b/src/Symfony/Component/DependencyInjection/Loader/PhpFileLoader.php
index 9acaa8cffbfb..a1314948f82a 100644
--- a/src/Symfony/Component/DependencyInjection/Loader/PhpFileLoader.php
+++ b/src/Symfony/Component/DependencyInjection/Loader/PhpFileLoader.php
@@ -36,9 +36,9 @@ class PhpFileLoader extends FileLoader
     protected bool $autoRegisterAliasesForSinglyImplementedInterfaces = false;
     private ?ConfigBuilderGeneratorInterface $generator;
 
-    public function __construct(ContainerBuilder $container, FileLocatorInterface $locator, ?string $env = null, ?ConfigBuilderGeneratorInterface $generator = null)
+    public function __construct(ContainerBuilder $container, FileLocatorInterface $locator, ?string $env = null, ?ConfigBuilderGeneratorInterface $generator = null, bool $prepend = false)
     {
-        parent::__construct($container, $locator, $env);
+        parent::__construct($container, $locator, $env, $prepend);
         $this->generator = $generator;
     }
 
@@ -145,10 +145,19 @@ class_exists(ContainerConfigurator::class);
 
         $callback(...$arguments);
 
-        /** @var ConfigBuilderInterface $configBuilder */
+        $this->loadFromExtensions($configBuilders);
+    }
+
+    /**
+     * @param iterable<ConfigBuilderInterface> $configBuilders
+     */
+    private function loadFromExtensions(iterable $configBuilders): void
+    {
         foreach ($configBuilders as $configBuilder) {
-            $containerConfigurator->extension($configBuilder->getExtensionAlias(), $configBuilder->toArray());
+            $this->loadExtensionConfig($configBuilder->getExtensionAlias(), $configBuilder->toArray());
         }
+
+        $this->loadExtensionConfigs();
     }
 
     /**
diff --git a/src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php b/src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php
index 6fedd9821ace..48122e9f36cc 100644
--- a/src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php
+++ b/src/Symfony/Component/DependencyInjection/Loader/XmlFileLoader.php
@@ -808,7 +808,7 @@ private function validateExtensions(\DOMDocument $dom, string $file): void
             }
 
             // can it be handled by an extension?
-            if (!$this->container->hasExtension($node->namespaceURI)) {
+            if (!$this->prepend && !$this->container->hasExtension($node->namespaceURI)) {
                 $extensionNamespaces = array_filter(array_map(fn (ExtensionInterface $ext) => $ext->getNamespace(), $this->container->getExtensions()));
                 throw new InvalidArgumentException(sprintf('There is no extension able to load the configuration for "%s" (in "%s"). Looked for namespace "%s", found "%s".', $node->tagName, $file, $node->namespaceURI, $extensionNamespaces ? implode('", "', $extensionNamespaces) : 'none'));
             }
@@ -830,8 +830,10 @@ private function loadFromExtensions(\DOMDocument $xml): void
                 $values = [];
             }
 
-            $this->container->loadFromExtension($node->namespaceURI, $values);
+            $this->loadExtensionConfig($node->namespaceURI, $values);
         }
+
+        $this->loadExtensionConfigs();
     }
 
     /**
diff --git a/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php b/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php
index c74e606be383..6215426542dc 100644
--- a/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php
+++ b/src/Symfony/Component/DependencyInjection/Loader/YamlFileLoader.php
@@ -129,22 +129,28 @@ public function load(mixed $resource, ?string $type = null): mixed
             return null;
         }
 
-        $this->loadContent($content, $path);
+        ++$this->importing;
+        try {
+            $this->loadContent($content, $path);
 
-        // per-env configuration
-        if ($this->env && isset($content['when@'.$this->env])) {
-            if (!\is_array($content['when@'.$this->env])) {
-                throw new InvalidArgumentException(sprintf('The "when@%s" key should contain an array in "%s". Check your YAML syntax.', $this->env, $path));
-            }
+            // per-env configuration
+            if ($this->env && isset($content['when@'.$this->env])) {
+                if (!\is_array($content['when@'.$this->env])) {
+                    throw new InvalidArgumentException(sprintf('The "when@%s" key should contain an array in "%s". Check your YAML syntax.', $this->env, $path));
+                }
 
-            $env = $this->env;
-            $this->env = null;
-            try {
-                $this->loadContent($content['when@'.$env], $path);
-            } finally {
-                $this->env = $env;
+                $env = $this->env;
+                $this->env = null;
+                try {
+                    $this->loadContent($content['when@'.$env], $path);
+                } finally {
+                    $this->env = $env;
+                }
             }
+        } finally {
+            --$this->importing;
         }
+        $this->loadExtensionConfigs();
 
         return null;
     }
@@ -802,7 +808,7 @@ private function validate(mixed $content, string $file): ?array
                 continue;
             }
 
-            if (!$this->container->hasExtension($namespace)) {
+            if (!$this->prepend && !$this->container->hasExtension($namespace)) {
                 $extensionNamespaces = array_filter(array_map(fn (ExtensionInterface $ext) => $ext->getAlias(), $this->container->getExtensions()));
                 throw new InvalidArgumentException(sprintf('There is no extension able to load the configuration for "%s" (in "%s"). Looked for namespace "%s", found "%s".', $namespace, $file, $namespace, $extensionNamespaces ? sprintf('"%s"', implode('", "', $extensionNamespaces)) : 'none'));
             }
@@ -941,12 +947,14 @@ private function loadFromExtensions(array $content): void
                 continue;
             }
 
-            if (!\is_array($values) && null !== $values) {
+            if (!\is_array($values)) {
                 $values = [];
             }
 
-            $this->container->loadFromExtension($namespace, $values);
+            $this->loadExtensionConfig($namespace, $values);
         }
+
+        $this->loadExtensionConfigs();
     }
 
     private function checkDefinition(string $id, array $definition, string $file): void
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Extension/AbstractExtensionTest.php b/src/Symfony/Component/DependencyInjection/Tests/Extension/AbstractExtensionTest.php
index 9180ab8342da..e98521b552ac 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Extension/AbstractExtensionTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Extension/AbstractExtensionTest.php
@@ -54,28 +54,55 @@ public function configure(DefinitionConfigurator $definition): void
         self::assertSame($expected, $this->processConfiguration($extension));
     }
 
-    public function testPrependAppendExtensionConfig()
+    public function testPrependExtensionConfig()
     {
         $extension = new class() extends AbstractExtension {
+            public function configure(DefinitionConfigurator $definition): void
+            {
+                $definition->rootNode()
+                    ->children()
+                        ->scalarNode('foo')->end()
+                    ->end();
+            }
+
             public function prependExtension(ContainerConfigurator $container, ContainerBuilder $builder): void
             {
-                // append config
-                $container->extension('third', ['foo' => 'append']);
+                // prepend config from plain array
+                $container->extension('third', ['foo' => 'pong'], true);
+
+                // prepend config from external file
+                $container->import('../Fixtures/config/packages/ping.yaml');
+            }
+
+            public function loadExtension(array $config, ContainerConfigurator $container, ContainerBuilder $builder): void
+            {
+                $container->parameters()->set('foo_param', $config['foo']);
+            }
 
-                // prepend config
-                $container->extension('third', ['foo' => 'prepend'], true);
+            public function getAlias(): string
+            {
+                return 'third';
             }
         };
 
         $container = $this->processPrependExtension($extension);
 
         $expected = [
-            ['foo' => 'prepend'],
+            ['foo' => 'a'],
+            ['foo' => 'c1'],
+            ['foo' => 'c2'],
+            ['foo' => 'b'],
+            ['foo' => 'ping'],
+            ['foo' => 'zaa'],
+            ['foo' => 'pong'],
             ['foo' => 'bar'],
-            ['foo' => 'append'],
         ];
 
         self::assertSame($expected, $container->getExtensionConfig('third'));
+
+        $container = $this->processLoadExtension($extension, $expected);
+
+        self::assertSame('bar', $container->getParameter('foo_param'));
     }
 
     public function testLoadExtension()
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/config/packages/ping.yaml b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/config/packages/ping.yaml
new file mode 100644
index 000000000000..e83b57070469
--- /dev/null
+++ b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/config/packages/ping.yaml
@@ -0,0 +1,10 @@
+imports:
+    - { resource: './third_a.yaml' }
+    - { resource: './third_b.yaml' }
+
+third:
+    foo: ping
+
+when@test:
+    third:
+        foo: zaa
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/config/packages/third_a.yaml b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/config/packages/third_a.yaml
new file mode 100644
index 000000000000..d15b3f589c68
--- /dev/null
+++ b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/config/packages/third_a.yaml
@@ -0,0 +1,2 @@
+third:
+    foo: a
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/config/packages/third_b.yaml b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/config/packages/third_b.yaml
new file mode 100644
index 000000000000..40b02dcbff8b
--- /dev/null
+++ b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/config/packages/third_b.yaml
@@ -0,0 +1,5 @@
+imports:
+    - { resource: './third_c.yaml' }
+
+third:
+    foo: b
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/config/packages/third_c.yaml b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/config/packages/third_c.yaml
new file mode 100644
index 000000000000..8ea12d674b40
--- /dev/null
+++ b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/config/packages/third_c.yaml
@@ -0,0 +1,6 @@
+third:
+    foo: c1
+
+when@test:
+    third:
+        foo: c2
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/xml/extensions/services1.xml b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/xml/extensions/services1.xml
index b1cc3904ab0d..0e77fc6e6bbc 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Fixtures/xml/extensions/services1.xml
+++ b/src/Symfony/Component/DependencyInjection/Tests/Fixtures/xml/extensions/services1.xml
@@ -11,9 +11,13 @@
         <service id="project.service.foo" class="BAR" public="true"/>
     </services>
 
-    <project:bar babar="babar">
+    <project:bar foo="ping">
         <another />
         <another2>%project.parameter.foo%</another2>
     </project:bar>
 
+    <when env="test">
+        <project:bar foo="zaa">
+        </project:bar>
+    </when>
 </container>
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Loader/PhpFileLoaderTest.php b/src/Symfony/Component/DependencyInjection/Tests/Loader/PhpFileLoaderTest.php
index a2b440b54d0e..39426d6b691d 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Loader/PhpFileLoaderTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Loader/PhpFileLoaderTest.php
@@ -47,6 +47,21 @@ public function testLoad()
         $this->assertEquals('foo', $container->getParameter('foo'), '->load() loads a PHP file resource');
     }
 
+    public function testPrependExtensionConfig()
+    {
+        $container = new ContainerBuilder();
+        $container->registerExtension(new \AcmeExtension());
+        $container->prependExtensionConfig('acme', ['foo' => 'bar']);
+        $loader = new PhpFileLoader($container, new FileLocator(\dirname(__DIR__).'/Fixtures'), 'prod', new ConfigBuilderGenerator(sys_get_temp_dir()), true);
+        $loader->load('config/config_builder.php');
+
+        $expected = [
+            ['color' => 'blue'],
+            ['foo' => 'bar'],
+        ];
+        $this->assertSame($expected, $container->getExtensionConfig('acme'));
+    }
+
     public function testConfigServices()
     {
         $fixtures = realpath(__DIR__.'/../Fixtures');
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Loader/XmlFileLoaderTest.php b/src/Symfony/Component/DependencyInjection/Tests/Loader/XmlFileLoaderTest.php
index 45c4d65b769c..ffe602704615 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Loader/XmlFileLoaderTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Loader/XmlFileLoaderTest.php
@@ -604,6 +604,20 @@ public function testExtensions()
         }
     }
 
+    public function testPrependExtensionConfig()
+    {
+        $container = new ContainerBuilder();
+        $container->prependExtensionConfig('http://www.example.com/schema/project', ['foo' => 'bar']);
+        $loader = new XmlFileLoader($container, new FileLocator(self::$fixturesPath.'/xml'), prepend: true);
+        $loader->load('extensions/services1.xml');
+
+        $expected = [
+            ['foo' => 'ping'],
+            ['foo' => 'bar'],
+        ];
+        $this->assertSame($expected, $container->getExtensionConfig('http://www.example.com/schema/project'));
+    }
+
     public function testExtensionInPhar()
     {
         if (\extension_loaded('suhosin') && !str_contains(\ini_get('suhosin.executor.include.whitelist'), 'phar')) {
diff --git a/src/Symfony/Component/DependencyInjection/Tests/Loader/YamlFileLoaderTest.php b/src/Symfony/Component/DependencyInjection/Tests/Loader/YamlFileLoaderTest.php
index 5be7ed74ad7f..e9a148b974d9 100644
--- a/src/Symfony/Component/DependencyInjection/Tests/Loader/YamlFileLoaderTest.php
+++ b/src/Symfony/Component/DependencyInjection/Tests/Loader/YamlFileLoaderTest.php
@@ -346,6 +346,20 @@ public function testExtensions()
         }
     }
 
+    public function testPrependExtensionConfig()
+    {
+        $container = new ContainerBuilder();
+        $container->prependExtensionConfig('project', ['foo' => 'bar']);
+        $loader = new YamlFileLoader($container, new FileLocator(self::$fixturesPath.'/yaml'), prepend: true);
+        $loader->load('services10.yml');
+
+        $expected = [
+            ['test' => '%project.parameter.foo%'],
+            ['foo' => 'bar'],
+        ];
+        $this->assertSame($expected, $container->getExtensionConfig('project'));
+    }
+
     public function testExtensionWithNullConfig()
     {
         $container = new ContainerBuilder();
diff --git a/src/Symfony/Component/HttpKernel/Bundle/BundleExtension.php b/src/Symfony/Component/HttpKernel/Bundle/BundleExtension.php
index b80bc21f25cf..8392218a29d9 100644
--- a/src/Symfony/Component/HttpKernel/Bundle/BundleExtension.php
+++ b/src/Symfony/Component/HttpKernel/Bundle/BundleExtension.php
@@ -51,7 +51,7 @@ public function prepend(ContainerBuilder $container): void
             $this->subject->prependExtension($configurator, $container);
         };
 
-        $this->executeConfiguratorCallback($container, $callback, $this->subject);
+        $this->executeConfiguratorCallback($container, $callback, $this->subject, true);
     }
 
     public function load(array $configs, ContainerBuilder $container): void