diff --git a/config/nextcloud-29/nextcloud-29-deprecations.php b/config/nextcloud-29/nextcloud-29-deprecations.php
new file mode 100644
index 0000000..1983bea
--- /dev/null
+++ b/config/nextcloud-29/nextcloud-29-deprecations.php
@@ -0,0 +1,12 @@
+<?php
+
+declare(strict_types=1);
+
+use Nextcloud\Rector\Rector\ReplaceIConfigWithIAppConfigRector;
+use Nextcloud\Rector\Set\NextcloudSets;
+use Rector\Config\RectorConfig;
+
+return static function (RectorConfig $rectorConfig): void {
+    $rectorConfig->sets([NextcloudSets::NEXTCLOUD_27]);
+    $rectorConfig->rule(ReplaceIConfigWithIAppConfigRector::class);
+};
diff --git a/config/nextcloud-33/nextcloud-33-deprecations.php b/config/nextcloud-33/nextcloud-33-deprecations.php
index 82ddfc3..1a7039b 100644
--- a/config/nextcloud-33/nextcloud-33-deprecations.php
+++ b/config/nextcloud-33/nextcloud-33-deprecations.php
@@ -9,7 +9,7 @@
 use Rector\Php80\ValueObject\AnnotationToAttribute;
 
 return static function (RectorConfig $rectorConfig): void {
-    $rectorConfig->sets([NextcloudSets::NEXTCLOUD_27]);
+    $rectorConfig->sets([NextcloudSets::NEXTCLOUD_29]);
     $rectorConfig->rule(ReplaceFetchAllMethodCallRector::class);
     $rectorConfig->ruleWithConfiguration(
         AnnotationToAttributeRector::class,
diff --git a/src/Rector/ReplaceIConfigWithIAppConfigRector.php b/src/Rector/ReplaceIConfigWithIAppConfigRector.php
new file mode 100644
index 0000000..8a1e099
--- /dev/null
+++ b/src/Rector/ReplaceIConfigWithIAppConfigRector.php
@@ -0,0 +1,257 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace Nextcloud\Rector\Rector;
+
+use PHPStan\Type\ObjectType;
+use PhpParser\Modifiers;
+use PhpParser\Node;
+use PhpParser\Node\Expr\MethodCall;
+use PhpParser\Node\Expr\PropertyFetch;
+use PhpParser\Node\Expr\Variable;
+use PhpParser\Node\Identifier;
+use PhpParser\Node\Name\FullyQualified;
+use PhpParser\Node\Param;
+use PhpParser\Node\Stmt\ClassMethod;
+use PhpParser\Node\Stmt\Class_;
+use Rector\Rector\AbstractRector;
+use Rector\ValueObject\MethodName;
+use Symplify\RuleDocGenerator\ValueObject\CodeSample\CodeSample;
+use Symplify\RuleDocGenerator\ValueObject\RuleDefinition;
+
+use function array_keys;
+use function is_string;
+
+final class ReplaceIConfigWithIAppConfigRector extends AbstractRector
+{
+    private const APP_CONFIG_CLASS = 'OCP\IAppConfig';
+
+    /**
+     * Map of deprecated \OCP\IConfig methods to their \OCP\IAppConfig replacements.
+     * The argument lists are forwarded as-is; the new methods accept additional
+     * optional parameters that default to a behaviour matching the old methods.
+     */
+    private const METHOD_MAP = [
+        'getAppValue' => 'getValue',
+        'getAppKeys' => 'getKeys',
+        'setAppValue' => 'setValue',
+        'deleteAppValue' => 'deleteKey',
+        'deleteAppValues' => 'deleteApp',
+    ];
+
+    public function getRuleDefinition(): RuleDefinition
+    {
+        return new RuleDefinition(
+            'Replace deprecated \OCP\IConfig app-config methods with their \OCP\IAppConfig counterparts,'
+            . ' injecting IAppConfig alongside the existing IConfig.',
+            [
+                new CodeSample(
+                    <<<'CODE_SAMPLE'
+use OCP\IConfig;
+
+class SomeClass
+{
+    public function __construct(private IConfig $config) {}
+
+    public function run(): string
+    {
+        return $this->config->getAppValue('myapp', 'mykey', 'default');
+    }
+}
+CODE_SAMPLE,
+                    <<<'CODE_SAMPLE'
+use OCP\IAppConfig;
+use OCP\IConfig;
+
+class SomeClass
+{
+    public function __construct(private IConfig $config, private IAppConfig $appConfig) {}
+
+    public function run(): string
+    {
+        return $this->appConfig->getValueString('myapp', 'mykey', 'default');
+    }
+}
+CODE_SAMPLE,
+                ),
+            ],
+        );
+    }
+
+    /**
+     * @return array<class-string<Node>>
+     */
+    public function getNodeTypes(): array
+    {
+        return [Class_::class];
+    }
+
+    public function refactor(Node $node): ?Node
+    {
+        if (!($node instanceof Class_)) {
+            return null;
+        }
+
+        $constructor = $node->getMethod(MethodName::CONSTRUCT);
+        if (!$constructor instanceof ClassMethod) {
+            return null;
+        }
+
+        $iConfigPropertyNames = $this->collectIConfigPromotedPropertyNames($constructor);
+        if ($iConfigPropertyNames === []) {
+            return null;
+        }
+
+        $callsToRewrite = $this->collectDeprecatedAppConfigCalls($node, $iConfigPropertyNames);
+        if ($callsToRewrite === []) {
+            return null;
+        }
+
+        $appConfigName = $this->findExistingAppConfigPropertyName($constructor);
+        if ($appConfigName === null) {
+            $appConfigName = $this->makeUniquePropertyName($constructor, 'appConfig');
+            $constructor->params[] = $this->buildPromotedAppConfigParam($appConfigName);
+        }
+
+        foreach ($callsToRewrite as $call) {
+            $oldMethodName = $this->getName($call->name);
+            if ($oldMethodName === null || !isset(self::METHOD_MAP[$oldMethodName])) {
+                continue;
+            }
+            /** @var PropertyFetch $propertyFetch */
+            $propertyFetch = $call->var;
+            $propertyFetch->name = new Identifier($appConfigName);
+            $call->name = new Identifier(self::METHOD_MAP[$oldMethodName]);
+        }
+
+        return $node;
+    }
+
+    /**
+     * @return list<string>
+     */
+    private function collectIConfigPromotedPropertyNames(ClassMethod $constructor): array
+    {
+        $names = [];
+        foreach ($constructor->getParams() as $param) {
+            if ($param->flags === 0) {
+                continue;
+            }
+            if (!$this->isObjectType($param, new ObjectType('OCP\IConfig'))) {
+                continue;
+            }
+            $name = $this->getName($param->var);
+            if (is_string($name)) {
+                $names[] = $name;
+            }
+        }
+
+        return $names;
+    }
+
+    /**
+     * @param list<string> $propertyNames
+     *
+     * @return list<MethodCall>
+     */
+    private function collectDeprecatedAppConfigCalls(Class_ $class, array $propertyNames): array
+    {
+        $deprecatedMethods = array_keys(self::METHOD_MAP);
+        $calls = [];
+        foreach ($class->getMethods() as $classMethod) {
+            $stmts = $classMethod->getStmts();
+            if ($stmts === null) {
+                continue;
+            }
+            $this->traverseNodesWithCallable(
+                $stmts,
+                function (Node $subNode) use ($propertyNames, $deprecatedMethods, &$calls): ?Node {
+                    if (!$subNode instanceof MethodCall) {
+                        return null;
+                    }
+                    if (!$this->isNames($subNode->name, $deprecatedMethods)) {
+                        return null;
+                    }
+                    if (!$subNode->var instanceof PropertyFetch) {
+                        return null;
+                    }
+                    $propertyFetch = $subNode->var;
+                    if (!$propertyFetch->var instanceof Variable) {
+                        return null;
+                    }
+                    if (!$this->isName($propertyFetch->var, 'this')) {
+                        return null;
+                    }
+                    foreach ($propertyNames as $propertyName) {
+                        if ($this->isName($propertyFetch->name, $propertyName)) {
+                            $calls[] = $subNode;
+
+                            break;
+                        }
+                    }
+
+                    return null;
+                },
+            );
+        }
+
+        return $calls;
+    }
+
+    private function findExistingAppConfigPropertyName(ClassMethod $constructor): ?string
+    {
+        foreach ($constructor->getParams() as $param) {
+            if ($param->flags === 0) {
+                continue;
+            }
+            if (!$this->isObjectType($param, new ObjectType(self::APP_CONFIG_CLASS))) {
+                continue;
+            }
+            $name = $this->getName($param->var);
+            if (is_string($name)) {
+                return $name;
+            }
+        }
+
+        return null;
+    }
+
+    private function makeUniquePropertyName(ClassMethod $constructor, string $desired): string
+    {
+        $taken = [];
+        foreach ($constructor->getParams() as $param) {
+            $name = $this->getName($param->var);
+            if (is_string($name)) {
+                $taken[$name] = true;
+            }
+        }
+        if (!isset($taken[$desired])) {
+            return $desired;
+        }
+        $i = 2;
+        while (isset($taken[$desired . $i])) {
+            $i++;
+        }
+
+        return $desired . $i;
+    }
+
+    private function buildPromotedAppConfigParam(string $name): Param
+    {
+        return new Param(
+            new Variable($name),
+            null,
+            new FullyQualified('OCP\IAppConfig'),
+            false,
+            false,
+            [],
+            Modifiers::PRIVATE,
+        );
+    }
+}
diff --git a/src/Set/NextcloudSets.php b/src/Set/NextcloudSets.php
index 35468c6..e6f37ea 100644
--- a/src/Set/NextcloudSets.php
+++ b/src/Set/NextcloudSets.php
@@ -10,9 +10,9 @@ final class NextcloudSets
     public const NEXTCLOUD_26 = __DIR__ . '/../../config/nextcloud-26/nextcloud-26-deprecations.php';
     public const NEXTCLOUD_27 = __DIR__ . '/../../config/nextcloud-27/nextcloud-27-deprecations.php';
     public const NEXTCLOUD_28 = self::NEXTCLOUD_27;
-    public const NEXTCLOUD_29 = self::NEXTCLOUD_27;
-    public const NEXTCLOUD_30 = self::NEXTCLOUD_27;
-    public const NEXTCLOUD_31 = self::NEXTCLOUD_27;
-    public const NEXTCLOUD_32 = self::NEXTCLOUD_27;
+    public const NEXTCLOUD_29 = __DIR__ . '/../../config/nextcloud-29/nextcloud-29-deprecations.php';
+    public const NEXTCLOUD_30 = self::NEXTCLOUD_29;
+    public const NEXTCLOUD_31 = self::NEXTCLOUD_30;
+    public const NEXTCLOUD_32 = self::NEXTCLOUD_31;
     public const NEXTCLOUD_33 = __DIR__ . '/../../config/nextcloud-33/nextcloud-33-deprecations.php';
 }
diff --git a/tests/Rector/ReplaceIConfigWithIAppConfigRector/Fixture/test_fixture.php.inc b/tests/Rector/ReplaceIConfigWithIAppConfigRector/Fixture/test_fixture.php.inc
new file mode 100644
index 0000000..20a175a
--- /dev/null
+++ b/tests/Rector/ReplaceIConfigWithIAppConfigRector/Fixture/test_fixture.php.inc
@@ -0,0 +1,60 @@
+<?php
+
+/*
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace Nextcloud\Rector\Test\Rector\ReplaceIConfigWithIAppConfigRector\Fixture;
+
+use OCP\IConfig;
+
+class SomeClass
+{
+    public function __construct(private IConfig $config)
+    {
+    }
+
+    public function run(): void
+    {
+        $this->config->getAppValue('myapp', 'mykey');
+        $this->config->getAppValue('myapp', 'mykey', 'default');
+        $this->config->getAppKeys('myapp');
+        $this->config->setAppValue('myapp', 'mykey', 'value');
+        $this->config->deleteAppValue('myapp', 'mykey');
+        $this->config->deleteAppValues('myapp');
+    }
+}
+
+?>
+-----
+<?php
+
+/*
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace Nextcloud\Rector\Test\Rector\ReplaceIConfigWithIAppConfigRector\Fixture;
+
+use OCP\IAppConfig;
+use OCP\IConfig;
+
+class SomeClass
+{
+    public function __construct(private IConfig $config, private IAppConfig $appConfig)
+    {
+    }
+
+    public function run(): void
+    {
+        $this->appConfig->getValue('myapp', 'mykey');
+        $this->appConfig->getValue('myapp', 'mykey', 'default');
+        $this->appConfig->getKeys('myapp');
+        $this->appConfig->setValue('myapp', 'mykey', 'value');
+        $this->appConfig->deleteKey('myapp', 'mykey');
+        $this->appConfig->deleteApp('myapp');
+    }
+}
+
+?>
diff --git a/tests/Rector/ReplaceIConfigWithIAppConfigRector/ReplaceIConfigWithIAppConfigRectorTest.php b/tests/Rector/ReplaceIConfigWithIAppConfigRector/ReplaceIConfigWithIAppConfigRectorTest.php
new file mode 100644
index 0000000..6569443
--- /dev/null
+++ b/tests/Rector/ReplaceIConfigWithIAppConfigRector/ReplaceIConfigWithIAppConfigRectorTest.php
@@ -0,0 +1,33 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+namespace Nextcloud\Rector\Test\Rector\ReplaceIConfigWithIAppConfigRector;
+
+use Iterator;
+use PHPUnit\Framework\Attributes\DataProvider;
+use Rector\Testing\PHPUnit\AbstractRectorTestCase;
+
+final class ReplaceIConfigWithIAppConfigRectorTest extends AbstractRectorTestCase
+{
+    #[DataProvider('provideData')]
+    public function test(string $filePath): void
+    {
+        $this->doTestFile($filePath);
+    }
+
+    public static function provideData(): Iterator
+    {
+        return self::yieldFilesFromDirectory(__DIR__ . '/Fixture');
+    }
+
+    public function provideConfigFilePath(): string
+    {
+        return __DIR__ . '/config/config.php';
+    }
+}
diff --git a/tests/Rector/ReplaceIConfigWithIAppConfigRector/config/config.php b/tests/Rector/ReplaceIConfigWithIAppConfigRector/config/config.php
new file mode 100644
index 0000000..741eb58
--- /dev/null
+++ b/tests/Rector/ReplaceIConfigWithIAppConfigRector/config/config.php
@@ -0,0 +1,17 @@
+<?php
+
+declare(strict_types=1);
+
+/*
+ * SPDX-FileCopyrightText: 2026 Nextcloud GmbH and Nextcloud contributors
+ * SPDX-License-Identifier: AGPL-3.0-or-later
+ */
+
+use Nextcloud\Rector\Rector\ReplaceIConfigWithIAppConfigRector;
+use Rector\Config\RectorConfig;
+
+return RectorConfig::configure()
+    ->withImportNames(removeUnusedImports: false)
+    ->withRules([
+        ReplaceIConfigWithIAppConfigRector::class,
+    ]);