diff --git a/CHANGELOG.md b/CHANGELOG.md
index 04c1441..d37e050 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -2,6 +2,7 @@ Latest
 ------
 
 ### Changes
+* [#71](https://github.com/cleverage/rest-process-bundle/issues/71) Configuring a key under `clever_age_rest_process` is deprecated: the bundle has no configuration and the keys were ignored without notice (new internal `Configuration`, empty; notice when the container is compiled). They will be rejected in 4.0. Update documentation, add tests.
 * [#69](https://github.com/cleverage/rest-process-bundle/issues/69) The bundle throws exceptions implementing `ProcessExceptionInterface` of the process bundle instead of raw SPL exceptions (as [cleverage/process-bundle#317](https://github.com/cleverage/process-bundle/issues/317)): new `Exception\UnexpectedValueException`, extending the SPL exceptions thrown before (same messages, the existing `catch` keep working). `RestException` (and so `RestRequestException` and `MissingClientException`) implements `ProcessExceptionInterface`; `RequestTask` throws a `RestRequestException` instead of a raw `\Exception` for an invalid response code (same message). Add tests.
 * [#67](https://github.com/cleverage/rest-process-bundle/issues/67) Composer: require PHP `^8.2` instead of `>=8.2` (PHP 9 is no longer accepted before being tested), remove the authorization of the `symfony/flex` plugin, which is not required (the CI installs it globally), as [cleverage/process-bundle#319](https://github.com/cleverage/process-bundle/issues/319).
 * [#62](https://github.com/cleverage/rest-process-bundle/issues/62) Define the public API (Symfony BC promise, as [cleverage/process-bundle#279](https://github.com/cleverage/process-bundle/issues/279)): `RequestTask`, `ClientRegistry` and `CleverAgeRestProcessBundle` are marked `@final since 3.3`, they will be `final` in 4.0: extending them triggers a deprecation with the Symfony `DebugClassLoader`. `Client` (extended by the applications) and the exceptions stay open. `CleverAgeRestProcessExtension` and `RegisterClientsPass` are marked `@internal`.
diff --git a/docs/index.md b/docs/index.md
index 5503118..511f89d 100644
--- a/docs/index.md
+++ b/docs/index.md
@@ -60,6 +60,8 @@ fetch:
     url_parameters: { codePostal: '{{ codePostal }}' }
 ```
 
+No option can be configured under `clever_age_rest_process`: a key there is ignored. Configuring one is deprecated since 3.3 (an `E_USER_DEPRECATED` error is triggered when the container is compiled), the keys will be rejected in 4.0.
+
 ## Documentation
 
 - Cookbooks
diff --git a/src/DependencyInjection/CleverAgeRestProcessExtension.php b/src/DependencyInjection/CleverAgeRestProcessExtension.php
index 96535c1..f0b9596 100644
--- a/src/DependencyInjection/CleverAgeRestProcessExtension.php
+++ b/src/DependencyInjection/CleverAgeRestProcessExtension.php
@@ -27,6 +27,18 @@ class CleverAgeRestProcessExtension extends Extension
 {
     public function load(array $configs, ContainerBuilder $container): void
     {
+        $keys = array_keys(array_merge(...$configs));
+        if ([] !== $keys) {
+            trigger_deprecation(
+                'cleverage/rest-process-bundle',
+                '3.3',
+                'Configuring "%s" is deprecated, the bundle has no configuration: the keys "%s" are ignored. They will be rejected in 4.0.',
+                $this->getAlias(),
+                implode('", "', $keys),
+            );
+        }
+        $this->processConfiguration(new Configuration(), $configs);
+
         $this->findServices($container, __DIR__.'/../../config/services');
 
         $container->registerAttributeForAutoconfiguration(
diff --git a/src/DependencyInjection/Configuration.php b/src/DependencyInjection/Configuration.php
new file mode 100644
index 0000000..8471a99
--- /dev/null
+++ b/src/DependencyInjection/Configuration.php
@@ -0,0 +1,37 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * This file is part of the CleverAge/RestProcessBundle package.
+ *
+ * Copyright (c) Clever-Age
+ *
+ * For the full copyright and license information, please view the LICENSE
+ * file that was distributed with this source code.
+ */
+
+namespace CleverAge\RestProcessBundle\DependencyInjection;
+
+use Symfony\Component\Config\Definition\Builder\ArrayNodeDefinition;
+use Symfony\Component\Config\Definition\Builder\TreeBuilder;
+use Symfony\Component\Config\Definition\ConfigurationInterface;
+
+/**
+ * The bundle has no option: the configured keys are ignored with a deprecation (see CleverAgeRestProcessExtension::load()), they will be
+ * rejected in 4.0.
+ *
+ * @internal
+ */
+final class Configuration implements ConfigurationInterface
+{
+    public function getConfigTreeBuilder(): TreeBuilder
+    {
+        $treeBuilder = new TreeBuilder('clever_age_rest_process');
+        /** @var ArrayNodeDefinition $rootNode */
+        $rootNode = $treeBuilder->getRootNode();
+        $rootNode->ignoreExtraKeys();
+
+        return $treeBuilder;
+    }
+}
diff --git a/tests/DependencyInjection/CleverAgeRestProcessExtensionTest.php b/tests/DependencyInjection/CleverAgeRestProcessExtensionTest.php
index 72d5098..d777824 100644
--- a/tests/DependencyInjection/CleverAgeRestProcessExtensionTest.php
+++ b/tests/DependencyInjection/CleverAgeRestProcessExtensionTest.php
@@ -15,6 +15,7 @@
 
 use CleverAge\RestProcessBundle\Attribute\AsRestClient;
 use CleverAge\RestProcessBundle\DependencyInjection\CleverAgeRestProcessExtension;
+use CleverAge\RestProcessBundle\DependencyInjection\Configuration;
 use CleverAge\RestProcessBundle\Registry\ClientRegistry;
 use CleverAge\RestProcessBundle\Task\RequestTask;
 use CleverAge\RestProcessBundle\Tests\Fixtures\AttributedClient;
@@ -29,6 +30,7 @@
 use Symfony\Component\Yaml\Yaml;
 
 #[CoversClass(CleverAgeRestProcessExtension::class)]
+#[CoversClass(Configuration::class)]
 #[CoversClass(AsRestClient::class)]
 class CleverAgeRestProcessExtensionTest extends TestCase
 {
@@ -110,4 +112,52 @@ public function testAsRestClientAttributeRegistersTheCode(): void
 
         self::assertSame([['code' => 'app_attributed']], $container->getDefinition('app.attributed')->getTag('cleverage.rest.client'));
     }
+
+    public function testConfigurationKeysAreDeprecated(): void
+    {
+        $deprecations = $this->collectDeprecations(static function (): void {
+            (new CleverAgeRestProcessExtension())->load([[], ['foo' => true], ['bar' => 1, 'foo' => false]], new ContainerBuilder());
+        });
+
+        self::assertSame(['Since cleverage/rest-process-bundle 3.3: Configuring "clever_age_rest_process" is deprecated, the bundle has no configuration: the keys "foo", "bar" are ignored. They will be rejected in 4.0.'], $deprecations);
+    }
+
+    public function testNoDeprecationWithoutConfigurationKey(): void
+    {
+        $deprecations = $this->collectDeprecations(static function (): void {
+            (new CleverAgeRestProcessExtension())->load([[], []], new ContainerBuilder());
+        });
+
+        self::assertSame([], $deprecations);
+    }
+
+    public function testConfigurationHasNoOption(): void
+    {
+        $configuration = (new CleverAgeRestProcessExtension())->getConfiguration([], new ContainerBuilder());
+
+        self::assertInstanceOf(Configuration::class, $configuration);
+        self::assertSame('clever_age_rest_process', $configuration->getConfigTreeBuilder()->buildTree()->getName());
+    }
+
+    /**
+     * @param callable(): void $callback
+     *
+     * @return list<string>
+     */
+    private function collectDeprecations(callable $callback): array
+    {
+        $deprecations = [];
+        set_error_handler(static function (int $errno, string $errstr) use (&$deprecations): bool {
+            $deprecations[] = $errstr;
+
+            return true;
+        }, \E_USER_DEPRECATED);
+        try {
+            $callback();
+        } finally {
+            restore_error_handler();
+        }
+
+        return $deprecations;
+    }
 }