diff --git a/.github/workflows/ci.yml b/.github/workflows/ci.yml
index 7367cca..b944d70 100644
--- a/.github/workflows/ci.yml
+++ b/.github/workflows/ci.yml
@@ -1,5 +1,11 @@
 name: Tests
-on: [push, pull_request]
+on:
+  push:
+    branches:
+      - '[0-9]+.x'
+      - '[0-9]+.[0-9]+'
+      - '[0-9]+.[0-9]+.x'
+  pull_request:
 
 jobs:
   build:
@@ -8,18 +14,18 @@ jobs:
     strategy:
       max-parallel: 10
       matrix:
-        php: [ '7.3', '7.4', '8.0', '8.1', '8.2']
+        php: [ '7.3', '7.4', '8.0', '8.1', '8.2', '8.3']
 
     steps:
       - name: Set up PHP
-        uses: shivammathur/setup-php@2.5.0
+        uses: shivammathur/setup-php@2.30.0
         with:
           php-version: ${{ matrix.php }}
           coverage: none
           tools: flex
 
       - name: Checkout code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Download dependencies
         run: composer update --no-interaction --prefer-dist --optimize-autoloader --prefer-stable
@@ -35,14 +41,14 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Set up PHP
-        uses: shivammathur/setup-php@2.5.0
+        uses: shivammathur/setup-php@2.30.0
         with:
           php-version: 7.3
           coverage: none
           tools: flex
 
       - name: Checkout code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Download dependencies
         run: composer update --no-interaction --prefer-dist --optimize-autoloader --prefer-stable --prefer-lowest
diff --git a/.github/workflows/static.yml b/.github/workflows/static.yml
index a8dc568..8de2f7d 100644
--- a/.github/workflows/static.yml
+++ b/.github/workflows/static.yml
@@ -1,5 +1,11 @@
-on: [push, pull_request]
 name: Static analysis
+on:
+  push:
+    branches:
+      - '[0-9]+.x'
+      - '[0-9]+.[0-9]+'
+      - '[0-9]+.[0-9]+.x'
+  pull_request:
 
 jobs:
   phpstan:
@@ -7,7 +13,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: PHPStan
         uses: docker://oskarstark/phpstan-ga
@@ -20,7 +26,7 @@ jobs:
     name: PHP-CS-Fixer
     runs-on: ubuntu-latest
     steps:
-      - uses: actions/checkout@v3
+      - uses: actions/checkout@v4
       - name: PHP-CS-Fixer
         uses: docker://oskarstark/php-cs-fixer-ga
         with:
@@ -31,7 +37,7 @@ jobs:
     runs-on: ubuntu-latest
     steps:
       - name: Checkout code
-        uses: actions/checkout@v3
+        uses: actions/checkout@v4
 
       - name: Psalm
         uses: docker://vimeo/psalm-github-actions
diff --git a/.gitignore b/.gitignore
index 5727179..254ab37 100644
--- a/.gitignore
+++ b/.gitignore
@@ -1,4 +1,4 @@
-/.php_cs.cache
+/.php-cs-fixer.cache
 /composer.lock
 /phpunit.xml
 /vendor/
diff --git a/composer.json b/composer.json
index e972831..d0a8ace 100644
--- a/composer.json
+++ b/composer.json
@@ -19,7 +19,8 @@
     "require-dev": {
         "phpunit/phpunit": "^8.0|^9.3",
         "php-http/client-integration-tests": "^3.0",
-        "phpspec/prophecy-phpunit": "^2.0"
+        "phpspec/prophecy-phpunit": "^2.0",
+        "php-http/message-factory": "^1.1"
     },
     "provide": {
         "php-http/client-implementation": "1.0",
@@ -36,11 +37,6 @@
             "Http\\Adapter\\Guzzle7\\Tests\\": "tests/"
         }
     },
-    "extra": {
-        "branch-alias": {
-            "dev-master": "1.x-dev"
-        }
-    },
     "scripts": {
         "test": "@php vendor/bin/phpunit"
     }
diff --git a/psalm.baseline.xml b/psalm.baseline.xml
index 96ab42c..d1aea73 100644
--- a/psalm.baseline.xml
+++ b/psalm.baseline.xml
@@ -5,4 +5,9 @@
       <code>$exception-&gt;getResponse()</code>
     </PossiblyNullArgument>
   </file>
+  <file src="src/Client.php">
+    <PossiblyUnusedMethod occurrences="1">
+      <code>createWithConfig</code>
+    </PossiblyUnusedMethod>
+  </file>
 </files>
diff --git a/src/Client.php b/src/Client.php
index a92ab06..51724a6 100644
--- a/src/Client.php
+++ b/src/Client.php
@@ -43,17 +43,11 @@ public static function createWithConfig(array $config): Client
         return new self(self::buildClient($config));
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function sendRequest(RequestInterface $request): ResponseInterface
     {
         return $this->sendAsyncRequest($request)->wait();
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function sendAsyncRequest(RequestInterface $request)
     {
         $promise = $this->guzzle->sendAsync($request);
diff --git a/src/Promise.php b/src/Promise.php
index b830216..815329d 100644
--- a/src/Promise.php
+++ b/src/Promise.php
@@ -53,13 +53,13 @@ public function __construct(PromiseInterface $promise, RequestInterface $request
             $this->state = self::FULFILLED;
 
             return $response;
-        }, function ($reason) use ($request) {
+        }, function ($reason) {
             $this->state = self::REJECTED;
 
             if ($reason instanceof HttplugException) {
                 $this->exception = $reason;
             } elseif ($reason instanceof GuzzleExceptions\GuzzleException) {
-                $this->exception = $this->handleException($reason, $request);
+                $this->exception = $this->handleException($reason);
             } elseif ($reason instanceof \Throwable) {
                 $this->exception = new HttplugException\TransferException('Invalid exception returned from Guzzle7', 0, $reason);
             } else {
@@ -70,31 +70,22 @@ public function __construct(PromiseInterface $promise, RequestInterface $request
         });
     }
 
-    /**
-     * {@inheritdoc}
-     */
-    public function then(callable $onFulfilled = null, callable $onRejected = null)
+    public function then(?callable $onFulfilled = null, ?callable $onRejected = null)
     {
         return new static($this->promise->then($onFulfilled, $onRejected), $this->request);
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function getState()
     {
         return $this->state;
     }
 
-    /**
-     * {@inheritdoc}
-     */
     public function wait($unwrap = true)
     {
         $this->promise->wait(false);
 
         if ($unwrap) {
-            if (self::REJECTED == $this->getState()) {
+            if (self::REJECTED === $this->getState()) {
                 throw $this->exception;
             }
 
@@ -107,7 +98,7 @@ public function wait($unwrap = true)
      *
      * @return HttplugException
      */
-    private function handleException(GuzzleExceptions\GuzzleException $exception, RequestInterface $request)
+    private function handleException(GuzzleExceptions\GuzzleException $exception)
     {
         if ($exception instanceof GuzzleExceptions\ConnectException) {
             return new HttplugException\NetworkException($exception->getMessage(), $exception->getRequest(), $exception);
diff --git a/tests/CurlHttpAdapterTest.php b/tests/CurlHttpAdapterTest.php
index 730b528..e53912f 100644
--- a/tests/CurlHttpAdapterTest.php
+++ b/tests/CurlHttpAdapterTest.php
@@ -11,9 +11,6 @@
  */
 class CurlHttpAdapterTest extends HttpAdapterTest
 {
-    /**
-     * {@inheritdoc}
-     */
     protected function createHandler()
     {
         return new CurlHandler();
diff --git a/tests/CurlHttpAsyncAdapterTest.php b/tests/CurlHttpAsyncAdapterTest.php
index 86aa4df..f5589f1 100644
--- a/tests/CurlHttpAsyncAdapterTest.php
+++ b/tests/CurlHttpAsyncAdapterTest.php
@@ -11,9 +11,6 @@
  */
 class CurlHttpAsyncAdapterTest extends HttpAsyncAdapterTest
 {
-    /**
-     * {@inheritdoc}
-     */
     protected function createHandler()
     {
         return new CurlHandler();
diff --git a/tests/DefaultHttpAdapterTest.php b/tests/DefaultHttpAdapterTest.php
index 8c32bc0..b4ac79a 100644
--- a/tests/DefaultHttpAdapterTest.php
+++ b/tests/DefaultHttpAdapterTest.php
@@ -13,9 +13,6 @@
  */
 class DefaultHttpAdapterTest extends HttpClientTest
 {
-    /**
-     * {@inheritdoc}
-     */
     protected function createHttpAdapter(): ClientInterface
     {
         return new Client();
diff --git a/tests/DefaultHttpAdapterWithConfigTest.php b/tests/DefaultHttpAdapterWithConfigTest.php
new file mode 100644
index 0000000..277f419
--- /dev/null
+++ b/tests/DefaultHttpAdapterWithConfigTest.php
@@ -0,0 +1,24 @@
+<?php
+
+declare(strict_types=1);
+
+use Http\Adapter\Guzzle7\Client;
+use Http\Client\Tests\HttpClientTest;
+use Psr\Http\Client\ClientInterface;
+
+/**
+ * @author David Buchmann <mail@davidbu.ch>
+ */
+class DefaultHttpAdapterWithConfigTest extends HttpClientTest
+{
+    protected function createHttpAdapter(): ClientInterface
+    {
+        $this->defaultHeaders['X-Test'] = 'configuration-value';
+
+        return Client::createWithConfig([
+            'headers' => [
+                'X-Test' => 'configuration-value',
+            ],
+        ]);
+    }
+}
diff --git a/tests/HttpAdapterTest.php b/tests/HttpAdapterTest.php
index 867ac6e..cb60c99 100644
--- a/tests/HttpAdapterTest.php
+++ b/tests/HttpAdapterTest.php
@@ -14,9 +14,6 @@
  */
 abstract class HttpAdapterTest extends HttpClientTest
 {
-    /**
-     * {@inheritdoc}
-     */
     protected function createHttpAdapter(): ClientInterface
     {
         return new Client(new GuzzleClient(['handler' => $this->createHandler()]));
diff --git a/tests/HttpAsyncAdapterTest.php b/tests/HttpAsyncAdapterTest.php
index a98a3e6..71ec7f4 100644
--- a/tests/HttpAsyncAdapterTest.php
+++ b/tests/HttpAsyncAdapterTest.php
@@ -14,9 +14,6 @@
  */
 abstract class HttpAsyncAdapterTest extends HttpAsyncClientTest
 {
-    /**
-     * {@inheritdoc}
-     */
     protected function createHttpAsyncClient(): HttpAsyncClient
     {
         return new Client(new GuzzleClient(['handler' => $this->createHandler()]));
diff --git a/tests/MultiCurlHttpAdapterTest.php b/tests/MultiCurlHttpAdapterTest.php
index 9f6db87..bae535d 100644
--- a/tests/MultiCurlHttpAdapterTest.php
+++ b/tests/MultiCurlHttpAdapterTest.php
@@ -11,9 +11,6 @@
  */
 class MultiCurlHttpAdapterTest extends HttpAdapterTest
 {
-    /**
-     * {@inheritdoc}
-     */
     protected function createHandler()
     {
         return new CurlMultiHandler();
diff --git a/tests/MultiCurlHttpAsyncAdapterTest.php b/tests/MultiCurlHttpAsyncAdapterTest.php
index 9cf4fda..40ac08f 100644
--- a/tests/MultiCurlHttpAsyncAdapterTest.php
+++ b/tests/MultiCurlHttpAsyncAdapterTest.php
@@ -11,9 +11,6 @@
  */
 class MultiCurlHttpAsyncAdapterTest extends HttpAsyncAdapterTest
 {
-    /**
-     * {@inheritdoc}
-     */
     protected function createHandler()
     {
         return new CurlMultiHandler();
diff --git a/tests/StreamHttpAdapterTest.php b/tests/StreamHttpAdapterTest.php
index cf742e4..36f45c8 100644
--- a/tests/StreamHttpAdapterTest.php
+++ b/tests/StreamHttpAdapterTest.php
@@ -11,9 +11,6 @@
  */
 class StreamHttpAdapterTest extends HttpAdapterTest
 {
-    /**
-     * {@inheritdoc}
-     */
     protected function createHandler()
     {
         return new StreamHandler();
diff --git a/tests/StreamHttpAsyncAdapterTest.php b/tests/StreamHttpAsyncAdapterTest.php
index a4f29f8..10564a4 100644
--- a/tests/StreamHttpAsyncAdapterTest.php
+++ b/tests/StreamHttpAsyncAdapterTest.php
@@ -11,9 +11,6 @@
  */
 class StreamHttpAsyncAdapterTest extends HttpAsyncAdapterTest
 {
-    /**
-     * {@inheritdoc}
-     */
     protected function createHandler()
     {
         return new StreamHandler();