diff --git a/app/Config/Filters.php b/app/Config/Filters.php
index ac37b414c45c..6ebe0f3100ac 100644
--- a/app/Config/Filters.php
+++ b/app/Config/Filters.php
@@ -50,7 +50,7 @@ class Filters extends BaseConfig
      * particular HTTP method (GET, POST, etc.).
      *
      * Example:
-     * 'post' => ['foo', 'bar']
+     * 'POST' => ['foo', 'bar']
      *
      * If you use this, you should disable auto-routing because auto-routing
      * permits any HTTP method to access a controller. Accessing the controller
diff --git a/app/Views/errors/html/error_exception.php b/app/Views/errors/html/error_exception.php
index 1c094d728872..d27d52fdc576 100644
--- a/app/Views/errors/html/error_exception.php
+++ b/app/Views/errors/html/error_exception.php
@@ -205,7 +205,7 @@
                         </tr>
                         <tr>
                             <td>HTTP Method</td>
-                            <td><?= esc(strtoupper($request->getMethod())) ?></td>
+                            <td><?= esc($request->getMethod()) ?></td>
                         </tr>
                         <tr>
                             <td>IP Address</td>
diff --git a/phpstan-baseline.php b/phpstan-baseline.php
index e584035c7ba1..9c06aa1d95b4 100644
--- a/phpstan-baseline.php
+++ b/phpstan-baseline.php
@@ -1926,11 +1926,6 @@
 	'count' => 2,
 	'path' => __DIR__ . '/system/Filters/Filters.php',
 ];
-$ignoreErrors[] = [
-	'message' => '#^Expression on left side of \\?\\? is not nullable\\.$#',
-	'count' => 1,
-	'path' => __DIR__ . '/system/Filters/Filters.php',
-];
 $ignoreErrors[] = [
 	'message' => '#^Only booleans are allowed in a negated boolean, array given\\.$#',
 	'count' => 1,
diff --git a/system/CodeIgniter.php b/system/CodeIgniter.php
index 68cb5a9f5497..3e12e4e121b1 100644
--- a/system/CodeIgniter.php
+++ b/system/CodeIgniter.php
@@ -21,6 +21,7 @@
 use CodeIgniter\HTTP\DownloadResponse;
 use CodeIgniter\HTTP\Exceptions\RedirectException;
 use CodeIgniter\HTTP\IncomingRequest;
+use CodeIgniter\HTTP\Method;
 use CodeIgniter\HTTP\RedirectResponse;
 use CodeIgniter\HTTP\Request;
 use CodeIgniter\HTTP\ResponsableInterface;
@@ -1027,7 +1028,7 @@ public function storePreviousURL($uri)
     public function spoofRequestMethod()
     {
         // Only works with POSTED forms
-        if (strtolower($this->request->getMethod()) !== 'post') {
+        if ($this->request->getMethod() !== Method::POST) {
             return;
         }
 
@@ -1038,7 +1039,7 @@ public function spoofRequestMethod()
         }
 
         // Only allows PUT, PATCH, DELETE
-        if (in_array(strtoupper($method), ['PUT', 'PATCH', 'DELETE'], true)) {
+        if (in_array($method, [Method::PUT, Method::PATCH, Method::DELETE], true)) {
             $this->request = $this->request->setMethod($method);
         }
     }
diff --git a/system/Debug/Exceptions.php b/system/Debug/Exceptions.php
index 0f66f060f349..12c1930279e2 100644
--- a/system/Debug/Exceptions.php
+++ b/system/Debug/Exceptions.php
@@ -128,7 +128,7 @@ public function exceptionHandler(Throwable $exception)
 
         if ($this->config->log === true && ! in_array($statusCode, $this->config->ignoreCodes, true)) {
             $uri       = $this->request->getPath() === '' ? '/' : $this->request->getPath();
-            $routeInfo = '[Method: ' . strtoupper($this->request->getMethod()) . ', Route: ' . $uri . ']';
+            $routeInfo = '[Method: ' . $this->request->getMethod() . ', Route: ' . $uri . ']';
 
             log_message('critical', "{message}\n{routeInfo}\nin {exFile} on line {exLine}.\n{trace}", [
                 'message'   => $exception->getMessage(),
diff --git a/system/Debug/Toolbar.php b/system/Debug/Toolbar.php
index 4a7a20632fd7..b2d54c5d52cc 100644
--- a/system/Debug/Toolbar.php
+++ b/system/Debug/Toolbar.php
@@ -79,7 +79,7 @@ public function run(float $startTime, float $totalTime, RequestInterface $reques
         $data = [];
         // Data items used within the view.
         $data['url']             = current_url();
-        $data['method']          = strtoupper($request->getMethod());
+        $data['method']          = $request->getMethod();
         $data['isAJAX']          = $request->isAJAX();
         $data['startTime']       = $startTime;
         $data['totalTime']       = $totalTime * 1000;
diff --git a/system/Filters/Filters.php b/system/Filters/Filters.php
index 8a28aeb0118e..9019c317aa1d 100644
--- a/system/Filters/Filters.php
+++ b/system/Filters/Filters.php
@@ -494,10 +494,28 @@ protected function processMethods()
             return;
         }
 
-        // Request method won't be set for CLI-based requests
-        $method = strtolower($this->request->getMethod()) ?? 'cli';
+        $method = $this->request->getMethod();
+
+        $found = false;
 
         if (array_key_exists($method, $this->config->methods)) {
+            $found = true;
+        }
+        // Checks lowercase HTTP method for backward compatibility.
+        // @deprecated 4.5.0
+        // @TODO remove this in the future.
+        elseif (array_key_exists(strtolower($method), $this->config->methods)) {
+            @trigger_error(
+                'Setting lowercase HTTP method key "' . strtolower($method) . '" is deprecated.'
+                . ' Use uppercase HTTP method like "' . strtoupper($method) . '".',
+                E_USER_DEPRECATED
+            );
+
+            $found  = true;
+            $method = strtolower($method);
+        }
+
+        if ($found) {
             if (config(Feature::class)->oldFilterOrder) {
                 $this->filters['before'] = array_merge($this->filters['before'], $this->config->methods[$method]);
             } else {
diff --git a/system/HTTP/CLIRequest.php b/system/HTTP/CLIRequest.php
index 878e8a1d66c6..2b12694d86b9 100644
--- a/system/HTTP/CLIRequest.php
+++ b/system/HTTP/CLIRequest.php
@@ -56,7 +56,7 @@ class CLIRequest extends Request
      *
      * @var string
      */
-    protected $method = 'cli';
+    protected $method = 'CLI';
 
     /**
      * Constructor
diff --git a/system/HTTP/CURLRequest.php b/system/HTTP/CURLRequest.php
index c8b3b9fe9f92..9f5cd61ab275 100644
--- a/system/HTTP/CURLRequest.php
+++ b/system/HTTP/CURLRequest.php
@@ -112,7 +112,7 @@ public function __construct(App $config, URI $uri, ?ResponseInterface $response
             throw HTTPException::forMissingCurl(); // @codeCoverageIgnore
         }
 
-        parent::__construct('GET', $uri);
+        parent::__construct(Method::GET, $uri);
 
         $this->responseOrig   = $response ?? new Response(config(App::class));
         $this->baseURI        = $uri->useRawQueryString();
@@ -130,7 +130,7 @@ public function __construct(App $config, URI $uri, ?ResponseInterface $response
      * Sends an HTTP request to the specified $url. If this is a relative
      * URL, it will be merged with $this->baseURI to form a complete URL.
      *
-     * @param string $method
+     * @param string $method HTTP method
      */
     public function request($method, string $url, array $options = []): ResponseInterface
     {
@@ -177,7 +177,7 @@ protected function resetOptions()
      */
     public function get(string $url, array $options = []): ResponseInterface
     {
-        return $this->request('get', $url, $options);
+        return $this->request(Method::GET, $url, $options);
     }
 
     /**
@@ -185,7 +185,7 @@ public function get(string $url, array $options = []): ResponseInterface
      */
     public function delete(string $url, array $options = []): ResponseInterface
     {
-        return $this->request('delete', $url, $options);
+        return $this->request('DELETE', $url, $options);
     }
 
     /**
@@ -193,7 +193,7 @@ public function delete(string $url, array $options = []): ResponseInterface
      */
     public function head(string $url, array $options = []): ResponseInterface
     {
-        return $this->request('head', $url, $options);
+        return $this->request('HEAD', $url, $options);
     }
 
     /**
@@ -201,7 +201,7 @@ public function head(string $url, array $options = []): ResponseInterface
      */
     public function options(string $url, array $options = []): ResponseInterface
     {
-        return $this->request('options', $url, $options);
+        return $this->request('OPTIONS', $url, $options);
     }
 
     /**
@@ -209,7 +209,7 @@ public function options(string $url, array $options = []): ResponseInterface
      */
     public function patch(string $url, array $options = []): ResponseInterface
     {
-        return $this->request('patch', $url, $options);
+        return $this->request('PATCH', $url, $options);
     }
 
     /**
@@ -217,7 +217,7 @@ public function patch(string $url, array $options = []): ResponseInterface
      */
     public function post(string $url, array $options = []): ResponseInterface
     {
-        return $this->request('post', $url, $options);
+        return $this->request(Method::POST, $url, $options);
     }
 
     /**
@@ -225,7 +225,7 @@ public function post(string $url, array $options = []): ResponseInterface
      */
     public function put(string $url, array $options = []): ResponseInterface
     {
-        return $this->request('put', $url, $options);
+        return $this->request(Method::PUT, $url, $options);
     }
 
     /**
@@ -339,17 +339,6 @@ protected function prepareURL(string $url): string
         );
     }
 
-    /**
-     * Get the request method. Overrides the Request class' method
-     * since users expect a different answer here.
-     *
-     * @param bool|false $upper Whether to return in upper or lower case.
-     */
-    public function getMethod(bool $upper = false): string
-    {
-        return ($upper) ? strtoupper($this->method) : strtolower($this->method);
-    }
-
     /**
      * Fires the actual cURL request.
      *
@@ -446,8 +435,6 @@ protected function applyRequestHeaders(array $curlOptions = []): array
      */
     protected function applyMethod(string $method, array $curlOptions): array
     {
-        $method = strtoupper($method);
-
         $this->method                       = $method;
         $curlOptions[CURLOPT_CUSTOMREQUEST] = $method;
 
@@ -458,7 +445,7 @@ protected function applyMethod(string $method, array $curlOptions): array
             return $this->applyBody($curlOptions);
         }
 
-        if ($method === 'PUT' || $method === 'POST') {
+        if ($method === Method::PUT || $method === Method::POST) {
             // See http://tools.ietf.org/html/rfc7230#section-3.3.2
             if ($this->header('content-length') === null && ! isset($this->config['multipart'])) {
                 $this->setHeader('Content-Length', '0');
diff --git a/system/HTTP/IncomingRequest.php b/system/HTTP/IncomingRequest.php
index e9365f79a85f..7641f42c4946 100755
--- a/system/HTTP/IncomingRequest.php
+++ b/system/HTTP/IncomingRequest.php
@@ -396,17 +396,18 @@ public function negotiate(string $type, array $supported, bool $strictMatch = fa
     /**
      * Checks this request type.
      *
-     * @param string $type HTTP verb or 'json' or 'ajax'
+     * @param string $type HTTP verb or 'json' or 'ajax'.
+     *                     HTTP verb should be case-sensitive, but this is case-insensitive.
      * @phpstan-param string|'get'|'post'|'put'|'delete'|'head'|'patch'|'options'|'json'|'ajax' $type
      */
     public function is(string $type): bool
     {
         $valueUpper = strtoupper($type);
 
-        $httpMethods = ['GET', 'POST', 'PUT', 'DELETE', 'HEAD', 'PATCH', 'OPTIONS'];
+        $httpMethods = Method::all();
 
         if (in_array($valueUpper, $httpMethods, true)) {
-            return strtoupper($this->getMethod()) === $valueUpper;
+            return $this->getMethod() === $valueUpper;
         }
 
         if ($valueUpper === 'JSON') {
diff --git a/system/HTTP/Method.php b/system/HTTP/Method.php
new file mode 100644
index 000000000000..7aae162b3cba
--- /dev/null
+++ b/system/HTTP/Method.php
@@ -0,0 +1,95 @@
+<?php
+
+/**
+ * This file is part of CodeIgniter 4 framework.
+ *
+ * (c) CodeIgniter Foundation <admin@codeigniter.com>
+ *
+ * For the full copyright and license information, please view
+ * the LICENSE file that was distributed with this source code.
+ */
+
+namespace CodeIgniter\HTTP;
+
+/**
+ * HTTP Method List
+ */
+class Method
+{
+    /**
+     * @see https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/CONNECT
+     */
+    public const CONNECT = 'CONNECT';
+
+    /**
+     * Idempotent
+     *
+     * @see https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/DELETE
+     */
+    public const DELETE = 'DELETE';
+
+    /**
+     * Safe, Idempotent, Cacheable
+     *
+     * @see https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/GET
+     */
+    public const GET = 'GET';
+
+    /**
+     * Safe, Idempotent, Cacheable
+     *
+     * @see https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/HEAD
+     */
+    public const HEAD = 'HEAD';
+
+    /**
+     * Safe, Idempotent
+     *
+     * @see https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/OPTIONS
+     */
+    public const OPTIONS = 'OPTIONS';
+
+    /**
+     * @see https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/PATCH
+     */
+    public const PATCH = 'PATCH';
+
+    /**
+     * @see https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/POST
+     */
+    public const POST = 'POST';
+
+    /**
+     * Idempotent
+     *
+     * @see https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/PUT
+     */
+    public const PUT = 'PUT';
+
+    /**
+     * Safe, Idempotent
+     *
+     * @see https://developer.mozilla.org/en-US/docs/Web/HTTP/Methods/TRACE
+     */
+    public const TRACE = 'TRACE';
+
+    /**
+     * Returns all HTTP methods.
+     *
+     * @return list<string>
+     */
+    public static function all(): array
+    {
+        return [
+            self::CONNECT,
+            self::DELETE,
+            self::GET,
+            self::HEAD,
+            self::OPTIONS,
+            self::PATCH,
+            self::POST,
+            self::PUT,
+            self::TRACE,
+        ];
+    }
+}
diff --git a/system/HTTP/OutgoingRequest.php b/system/HTTP/OutgoingRequest.php
index 698cde263bc1..b6f733f5ea3b 100644
--- a/system/HTTP/OutgoingRequest.php
+++ b/system/HTTP/OutgoingRequest.php
@@ -66,15 +66,13 @@ private function getHostFromUri(URI $uri): string
     }
 
     /**
-     * Get the request method.
+     * Retrieves the HTTP method of the request.
      *
-     * @param bool $upper Whether to return in upper or lower case.
-     *
-     * @deprecated The $upper functionality will be removed and this will revert to its PSR-7 equivalent
+     * @return string Returns the request method (always uppercase)
      */
-    public function getMethod(bool $upper = false): string
+    public function getMethod(): string
     {
-        return ($upper) ? strtoupper($this->method) : strtolower($this->method);
+        return $this->method;
     }
 
     /**
diff --git a/system/HTTP/OutgoingRequestInterface.php b/system/HTTP/OutgoingRequestInterface.php
index 3839b64fd8e1..b4a62dfde73f 100644
--- a/system/HTTP/OutgoingRequestInterface.php
+++ b/system/HTTP/OutgoingRequestInterface.php
@@ -21,14 +21,11 @@
 interface OutgoingRequestInterface extends MessageInterface
 {
     /**
-     * Get the request method.
-     * An extension of PSR-7's getMethod to allow casing.
+     * Retrieves the HTTP method of the request.
      *
-     * @param bool $upper Whether to return in upper or lower case.
-     *
-     * @deprecated The $upper functionality will be removed and this will revert to its PSR-7 equivalent
+     * @return string Returns the request method.
      */
-    public function getMethod(bool $upper = false): string;
+    public function getMethod(): string;
 
     /**
      * Return an instance with the provided HTTP method.
diff --git a/system/HTTP/Request.php b/system/HTTP/Request.php
index baf60c0305b6..1466175c7b8f 100644
--- a/system/HTTP/Request.php
+++ b/system/HTTP/Request.php
@@ -41,7 +41,7 @@ class Request extends OutgoingRequest implements RequestInterface
     public function __construct($config = null) // @phpstan-ignore-line
     {
         if (empty($this->method)) {
-            $this->method = $this->getServer('REQUEST_METHOD') ?? 'GET';
+            $this->method = $this->getServer('REQUEST_METHOD') ?? Method::GET;
         }
 
         if (empty($this->uri)) {
@@ -49,20 +49,6 @@ public function __construct($config = null) // @phpstan-ignore-line
         }
     }
 
-    /**
-     * Get the request method.
-     *
-     * @param bool $upper Whether to return in upper or lower case.
-     *
-     * @deprecated 4.0.5 The $upper functionality will be removed and this will revert to its PSR-7 equivalent
-     *
-     * @codeCoverageIgnore
-     */
-    public function getMethod(bool $upper = false): string
-    {
-        return ($upper) ? strtoupper($this->method) : strtolower($this->method);
-    }
-
     /**
      * Sets the request method. Used when spoofing the request.
      *
diff --git a/system/HTTP/ResponseTrait.php b/system/HTTP/ResponseTrait.php
index 9c4344e81c40..8d8cad504866 100644
--- a/system/HTTP/ResponseTrait.php
+++ b/system/HTTP/ResponseTrait.php
@@ -442,9 +442,9 @@ public function redirect(string $uri, string $method = 'auto', ?int $code = null
                 isset($_SERVER['SERVER_PROTOCOL'], $_SERVER['REQUEST_METHOD'])
                 && $this->getProtocolVersion() >= 1.1
             ) {
-                if ($_SERVER['REQUEST_METHOD'] === 'GET') {
+                if ($_SERVER['REQUEST_METHOD'] === Method::GET) {
                     $code = 302;
-                } elseif (in_array($_SERVER['REQUEST_METHOD'], ['POST', 'PUT', 'DELETE'], true)) {
+                } elseif (in_array($_SERVER['REQUEST_METHOD'], [Method::POST, Method::PUT, Method::DELETE], true)) {
                     // reference: https://en.wikipedia.org/wiki/Post/Redirect/Get
                     $code = 303;
                 } else {
diff --git a/system/Router/RouteCollection.php b/system/Router/RouteCollection.php
index 79b5e9de7d5d..05cb828976e7 100644
--- a/system/Router/RouteCollection.php
+++ b/system/Router/RouteCollection.php
@@ -1001,7 +1001,7 @@ public function presenter(string $name, ?array $options = null): RouteCollection
      * Specifies a single route to match for multiple HTTP Verbs.
      *
      * Example:
-     *  $route->match( ['get', 'post'], 'users/(:num)', 'users/$1);
+     *  $route->match( ['GET', 'POST'], 'users/(:num)', 'users/$1);
      *
      * @param array|Closure|string $to
      */
@@ -1012,6 +1012,18 @@ public function match(array $verbs = [], string $from = '', $to = '', ?array $op
         }
 
         foreach ($verbs as $verb) {
+            if ($verb === strtolower($verb)) {
+                @trigger_error(
+                    'Passing lowercase HTTP method "' . $verb . '" is deprecated.'
+                    . ' Use uppercase HTTP method like "' . strtoupper($verb) . '".',
+                    E_USER_DEPRECATED
+                );
+            }
+
+            /**
+             * @TODO We should use correct uppercase verb.
+             * @deprecated 4.5.0
+             */
             $verb = strtolower($verb);
 
             $this->{$verb}($from, $to, $options);
diff --git a/system/Security/Security.php b/system/Security/Security.php
index 4ba665639f36..9c28b82335b0 100644
--- a/system/Security/Security.php
+++ b/system/Security/Security.php
@@ -13,6 +13,7 @@
 
 use CodeIgniter\Cookie\Cookie;
 use CodeIgniter\HTTP\IncomingRequest;
+use CodeIgniter\HTTP\Method;
 use CodeIgniter\HTTP\Request;
 use CodeIgniter\HTTP\RequestInterface;
 use CodeIgniter\I18n\Time;
@@ -280,8 +281,8 @@ public function getCSRFTokenName(): string
     public function verify(RequestInterface $request)
     {
         // Protects POST, PUT, DELETE, PATCH
-        $method           = strtoupper($request->getMethod());
-        $methodsToProtect = ['POST', 'PUT', 'DELETE', 'PATCH'];
+        $method           = $request->getMethod();
+        $methodsToProtect = [Method::POST, Method::PUT, Method::DELETE, Method::PATCH];
         if (! in_array($method, $methodsToProtect, true)) {
             return $this;
         }
diff --git a/system/Test/FeatureTestTrait.php b/system/Test/FeatureTestTrait.php
index 6acef638f6b3..a254883865ad 100644
--- a/system/Test/FeatureTestTrait.php
+++ b/system/Test/FeatureTestTrait.php
@@ -36,7 +36,7 @@ trait FeatureTestTrait
      *
      * Example routes:
      * [
-     *    ['get', 'home', 'Home::index']
+     *    ['GET', 'home', 'Home::index'],
      * ]
      *
      * @param array|null $routes Array to set routes
@@ -51,10 +51,24 @@ protected function withRoutes(?array $routes = null)
             $collection->resetRoutes();
 
             foreach ($routes as $route) {
+                if ($route[0] === strtolower($route[0])) {
+                    @trigger_error(
+                        'Passing lowercase HTTP method "' . $route[0] . '" is deprecated.'
+                        . ' Use uppercase HTTP method like "' . strtoupper($route[0]) . '".',
+                        E_USER_DEPRECATED
+                    );
+                }
+
+                /**
+                 * @TODO For backward compatibility. Remove strtolower() in the future.
+                 * @deprecated 4.5.0
+                 */
+                $method = strtolower($route[0]);
+
                 if (isset($route[3])) {
-                    $collection->{$route[0]}($route[1], $route[2], $route[3]);
+                    $collection->{$method}($route[1], $route[2], $route[3]);
                 } else {
-                    $collection->{$route[0]}($route[1], $route[2]);
+                    $collection->{$method}($route[1], $route[2]);
                 }
             }
         }
diff --git a/system/Validation/Validation.php b/system/Validation/Validation.php
index 747ac66d9bc4..6313ea62c4fa 100644
--- a/system/Validation/Validation.php
+++ b/system/Validation/Validation.php
@@ -13,6 +13,7 @@
 
 use Closure;
 use CodeIgniter\HTTP\IncomingRequest;
+use CodeIgniter\HTTP\Method;
 use CodeIgniter\HTTP\RequestInterface;
 use CodeIgniter\Validation\Exceptions\ValidationException;
 use CodeIgniter\View\RendererInterface;
@@ -501,7 +502,7 @@ public function withRequest(RequestInterface $request): ValidationInterface
             return $this;
         }
 
-        if (in_array(strtolower($request->getMethod()), ['put', 'patch', 'delete'], true)
+        if (in_array($request->getMethod(), [Method::PUT, Method::PATCH, Method::DELETE], true)
             && strpos($request->getHeaderLine('Content-Type'), 'multipart/form-data') === false
         ) {
             $this->data = $request->getRawInput();
diff --git a/tests/system/CodeIgniterTest.php b/tests/system/CodeIgniterTest.php
index 505d1f5e5a7b..5d12863604f6 100644
--- a/tests/system/CodeIgniterTest.php
+++ b/tests/system/CodeIgniterTest.php
@@ -14,6 +14,7 @@
 use CodeIgniter\Config\Services;
 use CodeIgniter\Exceptions\ConfigException;
 use CodeIgniter\Exceptions\PageNotFoundException;
+use CodeIgniter\HTTP\Method;
 use CodeIgniter\HTTP\Response;
 use CodeIgniter\Router\Exceptions\RedirectException;
 use CodeIgniter\Router\RouteCollection;
@@ -721,7 +722,7 @@ public function testSpoofRequestMethodCanUsePUT(): void
         $_SERVER['SERVER_PROTOCOL'] = 'HTTP/1.1';
         $_SERVER['REQUEST_METHOD']  = 'POST';
 
-        $_POST['_method'] = 'PUT';
+        $_POST['_method'] = Method::PUT;
 
         $routes = \Config\Services::routes();
         $routes->setDefaultNamespace('App\Controllers');
@@ -733,7 +734,7 @@ public function testSpoofRequestMethodCanUsePUT(): void
         $this->codeigniter->run();
         ob_get_clean();
 
-        $this->assertSame('put', Services::incomingrequest()->getMethod());
+        $this->assertSame(Method::PUT, Services::incomingrequest()->getMethod());
     }
 
     public function testSpoofRequestMethodCannotUseGET(): void
@@ -758,7 +759,7 @@ public function testSpoofRequestMethodCannotUseGET(): void
         $this->codeigniter->run();
         ob_get_clean();
 
-        $this->assertSame('post', Services::incomingrequest()->getMethod());
+        $this->assertSame('POST', Services::incomingrequest()->getMethod());
     }
 
     /**
diff --git a/tests/system/Commands/Utilities/Routes/FilterFinderTest.php b/tests/system/Commands/Utilities/Routes/FilterFinderTest.php
index c59c9b9aee8e..23ecb5c97f0b 100644
--- a/tests/system/Commands/Utilities/Routes/FilterFinderTest.php
+++ b/tests/system/Commands/Utilities/Routes/FilterFinderTest.php
@@ -87,7 +87,7 @@ private function createFilters(array $config = []): Filters
                 ],
             ],
             'methods' => [
-                'get' => [],
+                'GET' => [],
             ],
             'filters' => [
                 'honeypot' => ['before' => ['form/*', 'survey/*']],
@@ -215,7 +215,7 @@ public function testFilterOrder()
                 ],
             ],
             'methods' => [
-                'get' => ['method1', 'method2'],
+                'GET' => ['method1', 'method2'],
             ],
             'filters' => [
                 'filter1' => ['before' => '*', 'after' => '*'],
@@ -280,7 +280,7 @@ public function testFilterOrderWithOldFilterOrder()
                 ],
             ],
             'methods' => [
-                'get' => ['method1', 'method2'],
+                'GET' => ['method1', 'method2'],
             ],
             'filters' => [
                 'filter1' => ['before' => '*', 'after' => '*'],
diff --git a/tests/system/Filters/FiltersTest.php b/tests/system/Filters/FiltersTest.php
index 7faf127f4647..f2412b289aa7 100644
--- a/tests/system/Filters/FiltersTest.php
+++ b/tests/system/Filters/FiltersTest.php
@@ -89,7 +89,7 @@ public function testProcessMethodDetectsCLI(): void
             'aliases' => ['foo' => ''],
             'globals' => [],
             'methods' => [
-                'cli' => ['foo'],
+                'CLI' => ['foo'],
             ],
         ];
         $filtersConfig = $this->createConfigFromArray(FiltersConfig::class, $config);
@@ -113,7 +113,7 @@ public function testProcessMethodDetectsGetRequests(): void
             'aliases' => ['foo' => ''],
             'globals' => [],
             'methods' => [
-                'get' => ['foo'],
+                'GET' => ['foo'],
             ],
         ];
         $filtersConfig = $this->createConfigFromArray(FiltersConfig::class, $config);
@@ -137,8 +137,8 @@ public function testProcessMethodRespectsMethod(): void
             ],
             'globals' => [],
             'methods' => [
-                'post' => ['foo'],
-                'get'  => ['bar'],
+                'POST' => ['foo'],
+                'GET'  => ['bar'],
             ],
         ];
         $filtersConfig = $this->createConfigFromArray(FiltersConfig::class, $config);
@@ -162,8 +162,8 @@ public function testProcessMethodIgnoresMethod(): void
             ],
             'globals' => [],
             'methods' => [
-                'post' => ['foo'],
-                'get'  => ['bar'],
+                'POST' => ['foo'],
+                'GET'  => ['bar'],
             ],
         ];
         $filtersConfig = $this->createConfigFromArray(FiltersConfig::class, $config);
@@ -348,8 +348,8 @@ public function testProcessMethodProcessesCombined(): void
                 ],
             ],
             'methods' => [
-                'post' => ['foo'],
-                'get'  => ['bar'],
+                'POST' => ['foo'],
+                'GET'  => ['bar'],
             ],
             'filters' => [
                 'foof' => [
@@ -391,7 +391,7 @@ public function testProcessMethodProcessesCombinedAfterForToolbar(): void
                 ],
             ],
             'methods' => [
-                'get' => ['bar'],
+                'GET' => ['bar'],
             ],
             'filters' => [
                 'foof' => [
diff --git a/tests/system/HTTP/CLIRequestTest.php b/tests/system/HTTP/CLIRequestTest.php
index e15f0fca4f87..3c6293131d70 100644
--- a/tests/system/HTTP/CLIRequestTest.php
+++ b/tests/system/HTTP/CLIRequestTest.php
@@ -525,8 +525,7 @@ public function testGetIPAddressDefault(): void
     public function testMethodReturnsRightStuff(): void
     {
         // Defaults method to CLI now.
-        $this->assertSame('cli', $this->request->getMethod());
-        $this->assertSame('CLI', $this->request->getMethod(true));
+        $this->assertSame('CLI', $this->request->getMethod());
     }
 
     public function testMethodIsCliReturnsAlwaysTrue(): void
diff --git a/tests/system/HTTP/CURLRequestDoNotShareOptionsTest.php b/tests/system/HTTP/CURLRequestDoNotShareOptionsTest.php
index d8e96424dae5..c9710616e2d2 100644
--- a/tests/system/HTTP/CURLRequestDoNotShareOptionsTest.php
+++ b/tests/system/HTTP/CURLRequestDoNotShareOptionsTest.php
@@ -103,7 +103,7 @@ public function testGetSetsCorrectMethod(): void
     {
         $this->request->get('http://example.com');
 
-        $this->assertSame('get', $this->request->getMethod());
+        $this->assertSame('GET', $this->request->getMethod());
 
         $options = $this->request->curl_options;
 
@@ -115,7 +115,7 @@ public function testDeleteSetsCorrectMethod(): void
     {
         $this->request->delete('http://example.com');
 
-        $this->assertSame('delete', $this->request->getMethod());
+        $this->assertSame('DELETE', $this->request->getMethod());
 
         $options = $this->request->curl_options;
 
@@ -127,7 +127,7 @@ public function testHeadSetsCorrectMethod(): void
     {
         $this->request->head('http://example.com');
 
-        $this->assertSame('head', $this->request->getMethod());
+        $this->assertSame('HEAD', $this->request->getMethod());
 
         $options = $this->request->curl_options;
 
@@ -139,7 +139,7 @@ public function testOptionsSetsCorrectMethod(): void
     {
         $this->request->options('http://example.com');
 
-        $this->assertSame('options', $this->request->getMethod());
+        $this->assertSame('OPTIONS', $this->request->getMethod());
 
         $options = $this->request->curl_options;
 
@@ -281,7 +281,7 @@ public function testPatchSetsCorrectMethod(): void
     {
         $this->request->patch('http://example.com');
 
-        $this->assertSame('patch', $this->request->getMethod());
+        $this->assertSame('PATCH', $this->request->getMethod());
 
         $options = $this->request->curl_options;
 
@@ -293,7 +293,7 @@ public function testPostSetsCorrectMethod(): void
     {
         $this->request->post('http://example.com');
 
-        $this->assertSame('post', $this->request->getMethod());
+        $this->assertSame('POST', $this->request->getMethod());
 
         $options = $this->request->curl_options;
 
@@ -305,7 +305,7 @@ public function testPutSetsCorrectMethod(): void
     {
         $this->request->put('http://example.com');
 
-        $this->assertSame('put', $this->request->getMethod());
+        $this->assertSame('PUT', $this->request->getMethod());
 
         $options = $this->request->curl_options;
 
@@ -322,19 +322,19 @@ public function testCustomMethodSetsCorrectMethod(): void
         $options = $this->request->curl_options;
 
         $this->assertArrayHasKey(CURLOPT_CUSTOMREQUEST, $options);
-        $this->assertSame('CUSTOM', $options[CURLOPT_CUSTOMREQUEST]);
+        $this->assertSame('custom', $options[CURLOPT_CUSTOMREQUEST]);
     }
 
     public function testRequestMethodGetsSanitized(): void
     {
         $this->request->request('<script>Custom</script>', 'http://example.com');
 
-        $this->assertSame('custom', $this->request->getMethod());
+        $this->assertSame('Custom', $this->request->getMethod());
 
         $options = $this->request->curl_options;
 
         $this->assertArrayHasKey(CURLOPT_CUSTOMREQUEST, $options);
-        $this->assertSame('CUSTOM', $options[CURLOPT_CUSTOMREQUEST]);
+        $this->assertSame('Custom', $options[CURLOPT_CUSTOMREQUEST]);
     }
 
     public function testRequestSetsBasicCurlOptions(): void
@@ -951,7 +951,7 @@ public function testPostFormEncoded(): void
             'form_params' => $params,
         ]);
 
-        $this->assertSame('post', $this->request->getMethod());
+        $this->assertSame('POST', $this->request->getMethod());
 
         $options = $this->request->curl_options;
 
@@ -974,7 +974,7 @@ public function testPostFormMultipart(): void
             'multipart' => $params,
         ]);
 
-        $this->assertSame('post', $this->request->getMethod());
+        $this->assertSame('POST', $this->request->getMethod());
 
         $options = $this->request->curl_options;
 
@@ -1022,7 +1022,7 @@ public function testJSONData(): void
             'json' => $params,
         ]);
 
-        $this->assertSame('post', $this->request->getMethod());
+        $this->assertSame('POST', $this->request->getMethod());
 
         $expected = json_encode($params);
         $this->assertSame(
diff --git a/tests/system/HTTP/CURLRequestTest.php b/tests/system/HTTP/CURLRequestTest.php
index 186284da6ba6..2ca18aa87282 100644
--- a/tests/system/HTTP/CURLRequestTest.php
+++ b/tests/system/HTTP/CURLRequestTest.php
@@ -103,7 +103,7 @@ public function testGetSetsCorrectMethod(): void
     {
         $this->request->get('http://example.com');
 
-        $this->assertSame('get', $this->request->getMethod());
+        $this->assertSame('GET', $this->request->getMethod());
 
         $options = $this->request->curl_options;
 
@@ -115,7 +115,7 @@ public function testDeleteSetsCorrectMethod(): void
     {
         $this->request->delete('http://example.com');
 
-        $this->assertSame('delete', $this->request->getMethod());
+        $this->assertSame('DELETE', $this->request->getMethod());
 
         $options = $this->request->curl_options;
 
@@ -127,7 +127,7 @@ public function testHeadSetsCorrectMethod(): void
     {
         $this->request->head('http://example.com');
 
-        $this->assertSame('head', $this->request->getMethod());
+        $this->assertSame('HEAD', $this->request->getMethod());
 
         $options = $this->request->curl_options;
 
@@ -139,7 +139,7 @@ public function testOptionsSetsCorrectMethod(): void
     {
         $this->request->options('http://example.com');
 
-        $this->assertSame('options', $this->request->getMethod());
+        $this->assertSame('OPTIONS', $this->request->getMethod());
 
         $options = $this->request->curl_options;
 
@@ -264,7 +264,7 @@ public function testPatchSetsCorrectMethod(): void
     {
         $this->request->patch('http://example.com');
 
-        $this->assertSame('patch', $this->request->getMethod());
+        $this->assertSame('PATCH', $this->request->getMethod());
 
         $options = $this->request->curl_options;
 
@@ -276,7 +276,7 @@ public function testPostSetsCorrectMethod(): void
     {
         $this->request->post('http://example.com');
 
-        $this->assertSame('post', $this->request->getMethod());
+        $this->assertSame('POST', $this->request->getMethod());
 
         $options = $this->request->curl_options;
 
@@ -288,7 +288,7 @@ public function testPutSetsCorrectMethod(): void
     {
         $this->request->put('http://example.com');
 
-        $this->assertSame('put', $this->request->getMethod());
+        $this->assertSame('PUT', $this->request->getMethod());
 
         $options = $this->request->curl_options;
 
@@ -305,19 +305,19 @@ public function testCustomMethodSetsCorrectMethod(): void
         $options = $this->request->curl_options;
 
         $this->assertArrayHasKey(CURLOPT_CUSTOMREQUEST, $options);
-        $this->assertSame('CUSTOM', $options[CURLOPT_CUSTOMREQUEST]);
+        $this->assertSame('custom', $options[CURLOPT_CUSTOMREQUEST]);
     }
 
     public function testRequestMethodGetsSanitized(): void
     {
         $this->request->request('<script>Custom</script>', 'http://example.com');
 
-        $this->assertSame('custom', $this->request->getMethod());
+        $this->assertSame('Custom', $this->request->getMethod());
 
         $options = $this->request->curl_options;
 
         $this->assertArrayHasKey(CURLOPT_CUSTOMREQUEST, $options);
-        $this->assertSame('CUSTOM', $options[CURLOPT_CUSTOMREQUEST]);
+        $this->assertSame('Custom', $options[CURLOPT_CUSTOMREQUEST]);
     }
 
     public function testRequestSetsBasicCurlOptions(): void
@@ -934,7 +934,7 @@ public function testPostFormEncoded(): void
             'form_params' => $params,
         ]);
 
-        $this->assertSame('post', $this->request->getMethod());
+        $this->assertSame('POST', $this->request->getMethod());
 
         $options = $this->request->curl_options;
 
@@ -957,7 +957,7 @@ public function testPostFormMultipart(): void
             'multipart' => $params,
         ]);
 
-        $this->assertSame('post', $this->request->getMethod());
+        $this->assertSame('POST', $this->request->getMethod());
 
         $options = $this->request->curl_options;
 
@@ -1005,7 +1005,7 @@ public function testJSONData(): void
             'json' => $params,
         ]);
 
-        $this->assertSame('post', $this->request->getMethod());
+        $this->assertSame('POST', $this->request->getMethod());
 
         $expected = json_encode($params);
         $this->assertSame($expected, $this->request->getBody());
diff --git a/tests/system/HTTP/IncomingRequestTest.php b/tests/system/HTTP/IncomingRequestTest.php
index b8d0680a19ae..dc537093632e 100644
--- a/tests/system/HTTP/IncomingRequestTest.php
+++ b/tests/system/HTTP/IncomingRequestTest.php
@@ -840,7 +840,7 @@ public function testGetFile(): void
     public function testSpoofing(): void
     {
         $this->request->setMethod('WINK');
-        $this->assertSame('wink', $this->request->getMethod());
+        $this->assertSame('WINK', $this->request->getMethod());
     }
 
     /**
diff --git a/tests/system/HTTP/OutgoingRequestTest.php b/tests/system/HTTP/OutgoingRequestTest.php
index 51b2bab6a3fe..d857297d49ef 100644
--- a/tests/system/HTTP/OutgoingRequestTest.php
+++ b/tests/system/HTTP/OutgoingRequestTest.php
@@ -44,8 +44,8 @@ public function testWithMethod(): void
 
         $newRequest = $request->withMethod('POST');
 
-        $this->assertSame('GET', strtoupper($request->getMethod()));
-        $this->assertSame('POST', strtoupper($newRequest->getMethod()));
+        $this->assertSame('GET', $request->getMethod());
+        $this->assertSame('POST', $newRequest->getMethod());
     }
 
     public function testWithUri(): void
diff --git a/tests/system/HTTP/RequestTest.php b/tests/system/HTTP/RequestTest.php
index be20b4ff8f5b..269156fc1982 100644
--- a/tests/system/HTTP/RequestTest.php
+++ b/tests/system/HTTP/RequestTest.php
@@ -639,7 +639,6 @@ public function testGetIPAddressThruProxyOutofSubnet(): void
     public function testMethodReturnsRightStuff(): void
     {
         // Defaults method to GET now.
-        $this->assertSame('get', $this->request->getMethod());
-        $this->assertSame('GET', $this->request->getMethod(true));
+        $this->assertSame('GET', $this->request->getMethod());
     }
 }
diff --git a/tests/system/Helpers/URLHelper/MiscUrlTest.php b/tests/system/Helpers/URLHelper/MiscUrlTest.php
index 04da4f7352fe..62a86b675fad 100644
--- a/tests/system/Helpers/URLHelper/MiscUrlTest.php
+++ b/tests/system/Helpers/URLHelper/MiscUrlTest.php
@@ -966,7 +966,7 @@ public function testUrlToMissingArgument(): void
 
         $routes = Services::routes();
         $routes->group('(:alpha)', static function ($routes): void {
-            $routes->match(['get'], 'login', 'Common\LoginController::loginView', ['as' => 'loginURL']);
+            $routes->match(['GET'], 'login', 'Common\LoginController::loginView', ['as' => 'loginURL']);
         });
 
         url_to('loginURL');
diff --git a/tests/system/HomeTest.php b/tests/system/HomeTest.php
index d7c132e9736d..915e5992b45e 100644
--- a/tests/system/HomeTest.php
+++ b/tests/system/HomeTest.php
@@ -28,7 +28,7 @@ public function testPageLoadsSuccessfully(): void
     {
         $this->withRoutes([
             [
-                'get',
+                'GET',
                 'home',
                 '\App\Controllers\Home::index',
             ],
diff --git a/tests/system/Router/RouteCollectionTest.php b/tests/system/Router/RouteCollectionTest.php
index 985326dcf66d..06ab63f3e151 100644
--- a/tests/system/Router/RouteCollectionTest.php
+++ b/tests/system/Router/RouteCollectionTest.php
@@ -15,6 +15,7 @@
 use CodeIgniter\Config\Services;
 use CodeIgniter\controller;
 use CodeIgniter\Exceptions\PageNotFoundException;
+use CodeIgniter\HTTP\Method;
 use CodeIgniter\Test\CIUnitTestCase;
 use Config\Modules;
 use Config\Routing;
@@ -144,11 +145,11 @@ public function testAddIgnoresDefaultNamespaceWhenExists(): void
 
     public function testAddWorksWithCurrentHTTPMethods(): void
     {
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
 
         $routes = $this->getCollector();
 
-        $routes->match(['get'], 'home', 'controller');
+        $routes->match(['GET'], 'home', 'controller');
 
         $expects = [
             'home' => '\controller',
@@ -176,11 +177,11 @@ public function testAddWithLeadingSlash(): void
 
     public function testMatchIgnoresInvalidHTTPMethods(): void
     {
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
 
         $routes = $this->getCollector();
 
-        $routes->match(['put'], 'home', 'controller');
+        $routes->match(['PUT'], 'home', 'controller');
 
         $routes = $routes->getRoutes();
 
@@ -189,7 +190,7 @@ public function testMatchIgnoresInvalidHTTPMethods(): void
 
     public function testAddWorksWithArrayOFHTTPMethods(): void
     {
-        Services::request()->setMethod('post');
+        Services::request()->setMethod(Method::POST);
 
         $routes = $this->getCollector();
 
@@ -696,7 +697,7 @@ public function testPresenterScaffoldsCorrectly(): void
 
     public function testResourcesWithCustomController(): void
     {
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
         $routes = $this->getCollector();
 
         $routes->resource('photos', ['controller' => '<script>gallery']);
@@ -713,7 +714,7 @@ public function testResourcesWithCustomController(): void
 
     public function testResourcesWithCustomPlaceholder(): void
     {
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
         $routes = $this->getCollector();
 
         $routes->resource('photos', ['placeholder' => ':num']);
@@ -730,7 +731,7 @@ public function testResourcesWithCustomPlaceholder(): void
 
     public function testResourcesWithDefaultPlaceholder(): void
     {
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
         $routes = $this->getCollector();
 
         $routes->setDefaultConstraint('num');
@@ -748,7 +749,7 @@ public function testResourcesWithDefaultPlaceholder(): void
 
     public function testResourcesWithBogusDefaultPlaceholder(): void
     {
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
         $routes = $this->getCollector();
 
         $routes->setDefaultConstraint(':num');
@@ -766,7 +767,7 @@ public function testResourcesWithBogusDefaultPlaceholder(): void
 
     public function testResourcesWithOnly(): void
     {
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
         $routes = $this->getCollector();
 
         $routes->resource('photos', ['only' => 'index']);
@@ -780,7 +781,7 @@ public function testResourcesWithOnly(): void
 
     public function testResourcesWithExcept(): void
     {
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
         $routes = $this->getCollector();
 
         $routes->resource('photos', ['except' => 'edit,new']);
@@ -811,23 +812,23 @@ public function testResourcesWithWebsafe(): void
 
     public function testMatchSupportsMultipleMethods(): void
     {
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
         $routes = $this->getCollector();
 
         $expected = ['here' => '\there'];
 
-        $routes->match(['get', 'post'], 'here', 'there');
+        $routes->match(['GET', 'POST'], 'here', 'there');
         $this->assertSame($expected, $routes->getRoutes());
 
-        Services::request()->setMethod('post');
+        Services::request()->setMethod(Method::POST);
         $routes = $this->getCollector();
-        $routes->match(['get', 'post'], 'here', 'there');
+        $routes->match(['GET', 'POST'], 'here', 'there');
         $this->assertSame($expected, $routes->getRoutes());
     }
 
     public function testGet(): void
     {
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
         $routes = $this->getCollector();
 
         $expected = ['here' => '\there'];
@@ -949,7 +950,7 @@ public function testEnvironmentRestricts(): void
     {
         // ENVIRONMENT should be 'testing'
 
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
         $routes = $this->getCollector();
 
         $expected = ['here' => '\there'];
@@ -1434,7 +1435,7 @@ static function (): void {},
 
     public function testRouteGroupWithFilterSimple(): void
     {
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
         $routes = $this->getCollector();
 
         $routes->group(
@@ -1453,7 +1454,7 @@ static function ($routes): void {
 
     public function testRouteGroupWithFilterWithParams(): void
     {
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
         $routes = $this->getCollector();
 
         $routes->group(
@@ -1471,7 +1472,7 @@ static function ($routes): void {
 
     public function test404OverrideNot(): void
     {
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
         $routes = $this->getCollector();
 
         $this->assertNull($routes->get404Override());
@@ -1479,7 +1480,7 @@ public function test404OverrideNot(): void
 
     public function test404OverrideString(): void
     {
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
         $routes = $this->getCollector();
 
         $routes->set404Override('Explode');
@@ -1488,7 +1489,7 @@ public function test404OverrideString(): void
 
     public function test404OverrideCallable(): void
     {
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
         $routes = $this->getCollector();
 
         $routes->set404Override(static function (): void {
@@ -1499,7 +1500,7 @@ public function test404OverrideCallable(): void
 
     public function testOffsetParameters(): void
     {
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
         $routes = $this->getCollector();
 
         $routes->get('users/(:num)', 'users/show/$1', ['offset' => 1]);
@@ -1515,7 +1516,7 @@ public function testOffsetParameters(): void
     public function testRouteToWithSubdomainMatch(): void
     {
         $_SERVER['HTTP_HOST'] = 'doc.example.com';
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
 
         $routes = $this->getCollector();
 
@@ -1527,7 +1528,7 @@ public function testRouteToWithSubdomainMatch(): void
     public function testRouteToWithSubdomainMismatch(): void
     {
         $_SERVER['HTTP_HOST'] = 'dev.example.com';
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
 
         $routes = $this->getCollector();
 
@@ -1539,7 +1540,7 @@ public function testRouteToWithSubdomainMismatch(): void
     public function testRouteToWithSubdomainNot(): void
     {
         $_SERVER['HTTP_HOST'] = 'example.com';
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
 
         $routes = $this->getCollector();
 
@@ -1551,7 +1552,7 @@ public function testRouteToWithSubdomainNot(): void
     public function testRouteToWithGenericSubdomainMatch(): void
     {
         $_SERVER['HTTP_HOST'] = 'doc.example.com';
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
 
         $routes = $this->getCollector();
 
@@ -1563,7 +1564,7 @@ public function testRouteToWithGenericSubdomainMatch(): void
     public function testRouteToWithGenericSubdomainMismatch(): void
     {
         $_SERVER['HTTP_HOST'] = 'dev.example.com';
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
 
         $routes = $this->getCollector();
 
@@ -1575,7 +1576,7 @@ public function testRouteToWithGenericSubdomainMismatch(): void
     public function testRouteToWithGenericSubdomainNot(): void
     {
         $_SERVER['HTTP_HOST'] = 'example.com';
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
 
         $routes = $this->getCollector();
 
@@ -1587,7 +1588,7 @@ public function testRouteToWithGenericSubdomainNot(): void
     public function testRouteToWithoutSubdomainMatch(): void
     {
         $_SERVER['HTTP_HOST'] = 'doc.example.com';
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
 
         $routes = $this->getCollector();
 
@@ -1599,7 +1600,7 @@ public function testRouteToWithoutSubdomainMatch(): void
     public function testRouteToWithoutSubdomainMismatch(): void
     {
         $_SERVER['HTTP_HOST'] = 'dev.example.com';
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
 
         $routes = $this->getCollector();
 
@@ -1611,7 +1612,7 @@ public function testRouteToWithoutSubdomainMismatch(): void
     public function testRouteToWithoutSubdomainNot(): void
     {
         $_SERVER['HTTP_HOST'] = 'example.com';
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
 
         $routes = $this->getCollector();
 
@@ -1628,7 +1629,7 @@ public function testRouteToWithoutSubdomainNot(): void
     public function testRouteOverwritingDifferentSubdomains(): void
     {
         $_SERVER['HTTP_HOST'] = 'doc.domain.com';
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
 
         $routes = $this->getCollector();
         $router = new Router($routes, Services::request());
@@ -1649,7 +1650,7 @@ public function testRouteOverwritingDifferentSubdomains(): void
     public function testRouteOverwritingTwoRules(): void
     {
         $_SERVER['HTTP_HOST'] = 'doc.domain.com';
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
 
         $routes = $this->getCollector();
         $router = new Router($routes, Services::request());
@@ -1670,7 +1671,7 @@ public function testRouteOverwritingTwoRules(): void
     public function testRouteOverwritingTwoRulesLastApplies(): void
     {
         $_SERVER['HTTP_HOST'] = 'doc.domain.com';
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
 
         $routes = $this->getCollector();
         $router = new Router($routes, Services::request());
@@ -1690,7 +1691,7 @@ public function testRouteOverwritingTwoRulesLastApplies(): void
     public function testRouteOverwritingMatchingSubdomain(): void
     {
         $_SERVER['HTTP_HOST'] = 'doc.domain.com';
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
 
         $routes = $this->getCollector();
         $router = new Router($routes, Services::request());
@@ -1710,7 +1711,7 @@ public function testRouteOverwritingMatchingSubdomain(): void
     public function testRouteOverwritingMatchingHost(): void
     {
         $_SERVER['HTTP_HOST'] = 'doc.domain.com';
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
 
         $routes = $this->getCollector();
         $router = new Router($routes, Services::request());
@@ -1734,7 +1735,7 @@ public function testRouteOverwritingMatchingHost(): void
      */
     public function testRouteDefaultNameSpace(): void
     {
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
         $routes = $this->getCollector();
         $router = new Router($routes, Services::request());
 
@@ -1748,7 +1749,7 @@ public function testRouteDefaultNameSpace(): void
 
     public function testZeroAsURIPath(): void
     {
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
         $routes = $this->getCollector();
         $router = new Router($routes, Services::request());
 
@@ -1796,7 +1797,7 @@ public function testAutoRoutesControllerNameReturnsFQCN($namespace): void
      */
     public function testRoutesControllerNameReturnsFQCN($namespace): void
     {
-        Services::request()->setMethod('get');
+        Services::request()->setMethod(Method::GET);
         $routes = $this->getCollector();
         $routes->setAutoRoute(false);
         $routes->setDefaultNamespace($namespace);
diff --git a/tests/system/Router/RouterTest.php b/tests/system/Router/RouterTest.php
index 60dd669172e5..130b0a2e437c 100644
--- a/tests/system/Router/RouterTest.php
+++ b/tests/system/Router/RouterTest.php
@@ -15,6 +15,7 @@
 use CodeIgniter\Exceptions\PageNotFoundException;
 use CodeIgniter\HTTP\Exceptions\RedirectException;
 use CodeIgniter\HTTP\IncomingRequest;
+use CodeIgniter\HTTP\Method;
 use CodeIgniter\Router\Exceptions\RouterException;
 use CodeIgniter\Test\CIUnitTestCase;
 use Config\Modules;
@@ -65,7 +66,7 @@ protected function setUp(): void
         $this->collection->map($routes);
 
         $this->request = Services::request();
-        $this->request->setMethod('get');
+        $this->request->setMethod(Method::GET);
     }
 
     public function testEmptyURIMatchesRoot(): void
diff --git a/tests/system/Test/ControllerTestTraitTest.php b/tests/system/Test/ControllerTestTraitTest.php
index ab45c6372d41..ac470ce3ce56 100644
--- a/tests/system/Test/ControllerTestTraitTest.php
+++ b/tests/system/Test/ControllerTestTraitTest.php
@@ -150,7 +150,7 @@ public function testRequestPassthrough(): void
             ->execute('popper');
 
         $req = $result->request();
-        $this->assertSame('get', $req->getMethod());
+        $this->assertSame('GET', $req->getMethod());
     }
 
     public function testFailureResponse(): void
diff --git a/tests/system/Test/FeatureTestTraitTest.php b/tests/system/Test/FeatureTestTraitTest.php
index 817f6ba9ea9a..76ffa0e83052 100644
--- a/tests/system/Test/FeatureTestTraitTest.php
+++ b/tests/system/Test/FeatureTestTraitTest.php
@@ -49,7 +49,7 @@ public function testCallGet(): void
     {
         $this->withRoutes([
             [
-                'get',
+                'GET',
                 'home',
                 static fn () => 'Hello World',
             ],
@@ -69,7 +69,7 @@ public function testCallGetAndUriString(): void
     {
         $this->withRoutes([
             [
-                'get',
+                'GET',
                 'foo/bar/1/2/3',
                 static fn () => 'Hello World',
             ],
@@ -85,7 +85,7 @@ public function testCallGetAndFilterReturnsResponse(): void
     {
         $this->withRoutes([
             [
-                'get',
+                'GET',
                 'admin',
                 static fn () => 'Admin Area',
                 ['filter' => 'test-redirectfilter'],
@@ -100,7 +100,7 @@ public function testClosureWithEcho()
     {
         $this->withRoutes([
             [
-                'get',
+                'GET',
                 'home',
                 static function () { echo 'test echo'; },
             ],
@@ -118,7 +118,7 @@ public function testCallPost(): void
     {
         $this->withRoutes([
             [
-                'post',
+                'POST',
                 'home',
                 static fn () => 'Hello Mars',
             ],
@@ -132,7 +132,7 @@ public function testCallPostWithBody(): void
     {
         $this->withRoutes([
             [
-                'post',
+                'POST',
                 'home',
                 static fn () => 'Hello ' . service('request')->getPost('foo') . '!',
             ],
@@ -146,7 +146,7 @@ public function testCallValidationTwice(): void
     {
         $this->withRoutes([
             [
-                'post',
+                'POST',
                 'section/create',
                 static function () {
                     $validation = Services::validation();
@@ -176,7 +176,7 @@ public function testCallPut(): void
     {
         $this->withRoutes([
             [
-                'put',
+                'PUT',
                 'home',
                 static fn () => 'Hello Pluto',
             ],
@@ -190,7 +190,7 @@ public function testCallPatch(): void
     {
         $this->withRoutes([
             [
-                'patch',
+                'PATCH',
                 'home',
                 static fn () => 'Hello Jupiter',
             ],
@@ -204,7 +204,7 @@ public function testCallOptions(): void
     {
         $this->withRoutes([
             [
-                'options',
+                'OPTIONS',
                 'home',
                 static fn () => 'Hello George',
             ],
@@ -218,7 +218,7 @@ public function testCallDelete(): void
     {
         $this->withRoutes([
             [
-                'delete',
+                'DELETE',
                 'home',
                 static fn () => 'Hello Wonka',
             ],
@@ -232,7 +232,7 @@ public function testSession(): void
     {
         $response = $this->withRoutes([
             [
-                'get',
+                'GET',
                 'home',
                 static fn () => 'Home',
             ],
@@ -254,7 +254,7 @@ public function testWithSessionNull(): void
 
         $response = $this->withRoutes([
             [
-                'get',
+                'GET',
                 'home',
                 static fn () => 'Home',
             ],
@@ -268,7 +268,7 @@ public function testReturns(): void
     {
         $this->withRoutes([
             [
-                'get',
+                'GET',
                 'home',
                 '\Tests\Support\Controllers\Popcorn::index',
             ],
@@ -281,7 +281,7 @@ public function testIgnores(): void
     {
         $this->withRoutes([
             [
-                'get',
+                'GET',
                 'home',
                 '\Tests\Support\Controllers\Popcorn::cat',
             ],
@@ -294,7 +294,7 @@ public function testEchoesWithParams(): void
     {
         $this->withRoutes([
             [
-                'get',
+                'GET',
                 'home',
                 '\Tests\Support\Controllers\Popcorn::canyon',
             ],
@@ -308,7 +308,7 @@ public function testEchoesWithQuery(): void
     {
         $this->withRoutes([
             [
-                'get',
+                'GET',
                 'home',
                 '\Tests\Support\Controllers\Popcorn::canyon',
             ],
@@ -373,7 +373,7 @@ public function testOpenCliRoutesFromHttpGot404($from, $to, $httpGet): void
 
         $this->withRoutes([
             [
-                'cli',
+                'CLI',
                 $from,
                 $to,
             ],
@@ -388,7 +388,7 @@ public function testIsOkWithRedirects(): void
     {
         $this->withRoutes([
             [
-                'get',
+                'GET',
                 'home',
                 '\Tests\Support\Controllers\Popcorn::goaway',
             ],
@@ -402,7 +402,7 @@ public function testCallGetWithParams(): void
     {
         $this->withRoutes([
             [
-                'get',
+                'GET',
                 'home',
                 static fn () => json_encode(Services::request()->getGet()),
             ],
@@ -429,7 +429,7 @@ public function testCallGetWithParamsAndREQUEST(): void
     {
         $this->withRoutes([
             [
-                'get',
+                'GET',
                 'home',
                 static fn () => json_encode(Services::request()->fetchGlobal('request')),
             ],
@@ -456,7 +456,7 @@ public function testCallPostWithParams(): void
     {
         $this->withRoutes([
             [
-                'post',
+                'POST',
                 'home',
                 static fn () => json_encode(Services::request()->getPost()),
             ],
@@ -483,7 +483,7 @@ public function testCallPostWithParamsAndREQUEST(): void
     {
         $this->withRoutes([
             [
-                'post',
+                'POST',
                 'home',
                 static fn () => json_encode(Services::request()->fetchGlobal('request')),
             ],
@@ -510,7 +510,7 @@ public function testCallPutWithJsonRequest(): void
     {
         $this->withRoutes([
             [
-                'put',
+                'PUT',
                 'home',
                 '\Tests\Support\Controllers\Popcorn::echoJson',
             ],
@@ -534,7 +534,7 @@ public function testCallPutWithJsonRequestAndREQUEST(): void
     {
         $this->withRoutes([
             [
-                'put',
+                'PUT',
                 'home',
                 static fn () => json_encode(Services::request()->fetchGlobal('request')),
             ],
@@ -558,7 +558,7 @@ public function testCallWithJsonRequest(): void
     {
         $this->withRoutes([
             [
-                'post',
+                'POST',
                 'home',
                 '\Tests\Support\Controllers\Popcorn::echoJson',
             ],
diff --git a/tests/system/Validation/ValidationTest.php b/tests/system/Validation/ValidationTest.php
index 780faece2751..28bee306ab88 100644
--- a/tests/system/Validation/ValidationTest.php
+++ b/tests/system/Validation/ValidationTest.php
@@ -849,7 +849,7 @@ public function testRawInput(): void
         $rules = [
             'role' => 'required|min_length[5]',
         ];
-        $result = $this->validation->withRequest($request->withMethod('patch'))->setRules($rules)->run();
+        $result = $this->validation->withRequest($request->withMethod('PATCH'))->setRules($rules)->run();
 
         $this->assertTrue($result);
         $this->assertSame([], $this->validation->getErrors());
@@ -874,7 +874,7 @@ public function testJsonInput(): void
             'role' => 'required|min_length[5]',
         ];
         $result = $this->validation
-            ->withRequest($request->withMethod('patch'))
+            ->withRequest($request->withMethod('PATCH'))
             ->setRules($rules)
             ->run();
 
@@ -930,7 +930,7 @@ public function testJsonInputObjectArray(): void
             'p' => 'required|array_count[2]',
         ];
         $result = $this->validation
-            ->withRequest($request->withMethod('patch'))
+            ->withRequest($request->withMethod('PATCH'))
             ->setRules($rules)
             ->run();
 
@@ -1113,7 +1113,7 @@ public function testRulesForArrayField(array $body, array $rules, array $results
         $request = new IncomingRequest($config, new SiteURI($config), http_build_query($body), new UserAgent());
 
         $this->validation->setRules($rules);
-        $this->validation->withRequest($request->withMethod('post'))->run($body);
+        $this->validation->withRequest($request->withMethod('POST'))->run($body);
         $this->assertSame($results, $this->validation->getErrors());
     }
 
@@ -1196,7 +1196,7 @@ public function testRulesForSingleRuleWithAsteriskWillReturnNoError(): void
             'name_user.*' => 'alpha_numeric',
         ]);
 
-        $this->validation->withRequest($request->withMethod('post'))->run();
+        $this->validation->withRequest($request->withMethod('POST'))->run();
         $this->assertSame([], $this->validation->getErrors());
     }
 
@@ -1231,7 +1231,7 @@ public function testRulesForSingleRuleWithAsteriskWillReturnError(): void
             'contacts.friends.*.name' => 'required',
         ]);
 
-        $this->validation->withRequest($request->withMethod('post'))->run();
+        $this->validation->withRequest($request->withMethod('POST'))->run();
         $this->assertSame([
             'id_user.0'               => 'The id_user.* field must contain only numbers.',
             'name_user.0'             => 'The name_user.* field may only contain alphabetical characters.',
@@ -1265,7 +1265,7 @@ public function testRulesForSingleRuleWithSingleValue(): void
             'id_user' => 'numeric',
         ]);
 
-        $this->validation->withRequest($request->withMethod('post'))->run();
+        $this->validation->withRequest($request->withMethod('POST'))->run();
         $this->assertSame([
             'id_user' => 'The id_user field must contain only numbers.',
         ], $this->validation->getErrors());
diff --git a/user_guide_src/source/changelogs/v4.5.0.rst b/user_guide_src/source/changelogs/v4.5.0.rst
index f2440ac5cc92..1530ecd813d8 100644
--- a/user_guide_src/source/changelogs/v4.5.0.rst
+++ b/user_guide_src/source/changelogs/v4.5.0.rst
@@ -21,6 +21,23 @@ BREAKING
 Behavior Changes
 ================
 
+Lowercase HTTP Method Name
+--------------------------
+
+For historical reasons, the framework used HTTP method names in lower case like
+"get", "post".
+But the method token is case-sensitive because it might be used as a gateway
+to object-based systems with case-sensitive method names. By convention,
+standardized methods are defined in all-uppercase US-ASCII letters.
+See https://www.rfc-editor.org/rfc/rfc9110#name-overview.
+
+Now the framework uses the correct HTTP method names like "GET", "POST".
+
+- ``Request::getMethod()`` returns uppercase HTTP methods.
+- ``CURLRequest::request()`` does not change the accepted HTTP methods to uppercase.
+
+See :ref:`upgrade-450-lowercase-http-method-name` for details.
+
 Filter Execution Order
 ----------------------
 
@@ -118,6 +135,16 @@ Others
 Removed Deprecated Items
 ========================
 
+Request
+-------
+
+- The ``$upper`` parameter in ``getMethod()`` in ``RequestInterface`` and ``Request``
+  has been removed. See :ref:`upgrade-450-lowercase-http-method-name`.
+- The deprecated ``isValidIP()`` method in ``RequestInterface`` and ``Request``
+  has been removed.
+- The visibility of the deprecated properties ``$uri`` and ``$config`` in
+  ``IncomingRequest`` has been changed to protected.
+
 Filters
 -------
 
@@ -183,10 +210,6 @@ Spark Commands
 Others
 ------
 
-- **IncomingRequest:** The visibility of the deprecated properties ``$uri`` and
-  ``$config`` has been changed to protected.
-- **RequestInterface:** The deprecated ``isValidIP()`` method has been removed.
-- **Request:** The deprecated ``isValidIP()`` method has been removed.
 - **Config:** The deprecated ``CodeIgniter\Config\Config`` class has been removed.
 
 Enhancements
@@ -258,6 +281,14 @@ Deprecations
   used.
 - **Response:** The constructor parameter ``$config`` has been deprecated. No
   longer used.
+- **Filters::** The feature that ``Filters`` accept the lowercase HTTP method keys
+  of ``Config\Filters::$methods`` has been deprecated. Use correct uppercase HTTP
+  method keys instead.
+- **RouteCollection:** The feature that the ``match()`` method accepts the lowercase
+  HTTP methods has been deprecated. Use correct uppercase HTTP methods instead.
+- **FeatureTestTrait:** The feature that the ``withRoutes()`` method accepts the
+  lowercase HTTP methods has been deprecated. Use correct uppercase HTTP methods
+  instead.
 
 Bugs Fixed
 **********
diff --git a/user_guide_src/source/incoming/filters/008.php b/user_guide_src/source/incoming/filters/008.php
index 8d417fd436aa..7538a199394a 100644
--- a/user_guide_src/source/incoming/filters/008.php
+++ b/user_guide_src/source/incoming/filters/008.php
@@ -9,8 +9,8 @@ class Filters extends BaseConfig
     // ...
 
     public array $methods = [
-        'post' => ['invalidchars', 'csrf'],
-        'get'  => ['csrf'],
+        'POST' => ['invalidchars', 'csrf'],
+        'GET'  => ['csrf'],
     ];
 
     // ...
diff --git a/user_guide_src/source/incoming/incomingrequest.rst b/user_guide_src/source/incoming/incomingrequest.rst
index c6db5b28fe4c..83a456196c1e 100644
--- a/user_guide_src/source/incoming/incomingrequest.rst
+++ b/user_guide_src/source/incoming/incomingrequest.rst
@@ -47,7 +47,10 @@ is()
 
 .. versionadded:: 4.3.0
 
-Since v4.3.0, you can use the ``is()`` method. It returns boolean.
+Since v4.3.0, you can use the ``is()`` method. It accepts a HTTP method, ``'ajax'``,
+or ``'json'``, and returns boolean.
+
+.. note:: HTTP method should be case-sensitive, but the parameter is case-insensitive.
 
 .. literalinclude:: incomingrequest/040.php
 
@@ -58,16 +61,16 @@ You can check the HTTP method that this request represents with the ``getMethod(
 
 .. literalinclude:: incomingrequest/005.php
 
-By default, the method is returned as a lower-case string (i.e., ``'get'``, ``'post'``, etc).
+The HTTP method is case-sensitive, and by convention, standardized methods are
+defined in all-uppercase US-ASCII letters.
 
-.. important:: The functionality to convert the return value to lower case is deprecated.
-    It will be removed in the future version, and this method will be PSR-7 equivalent.
+.. note:: Prior to v4.5.0, by default, the method was returned as a lower-case
+    string (i.e., ``'get'``, ``'post'``, etc). But it was a bug.
 
-You can get an
-uppercase version by wrapping the call in ``strtoupper()``::
+You can get an lowercase version by wrapping the call in ``strtolower()``::
 
-    // Returns 'GET'
-    $method = strtoupper($request->getMethod());
+    // Returns 'get'
+    $method = strtolower($request->getMethod());
 
 You can also check if the request was made through and HTTPS connection with the ``isSecure()`` method:
 
diff --git a/user_guide_src/source/incoming/incomingrequest/005.php b/user_guide_src/source/incoming/incomingrequest/005.php
index 3c93e74b7664..37e6f490ef85 100644
--- a/user_guide_src/source/incoming/incomingrequest/005.php
+++ b/user_guide_src/source/incoming/incomingrequest/005.php
@@ -1,4 +1,4 @@
 <?php
 
-// Returns 'post'
+// Returns 'POST'
 $method = $request->getMethod();
diff --git a/user_guide_src/source/incoming/request.rst b/user_guide_src/source/incoming/request.rst
index d15da89ec14e..545c42f7e019 100644
--- a/user_guide_src/source/incoming/request.rst
+++ b/user_guide_src/source/incoming/request.rst
@@ -57,16 +57,12 @@ Class Reference
         Accepts an optional second string parameter of ``ipv4`` or ``ipv6`` to specify
         an IP format. The default checks for both formats.
 
-    .. php:method:: getMethod([$upper = false])
+    .. php:method:: getMethod()
 
-        .. important:: Use of the ``$upper`` parameter is deprecated. It will be removed in future releases.
-
-        :param bool $upper: Whether to return the request method name in upper or lower case
         :returns: HTTP request method
         :rtype: string
 
-        Returns the ``$_SERVER['REQUEST_METHOD']``, with the option to set it
-        in uppercase or lowercase.
+        Returns the ``$_SERVER['REQUEST_METHOD']``.
 
         .. literalinclude:: request/003.php
 
diff --git a/user_guide_src/source/incoming/request/003.php b/user_guide_src/source/incoming/request/003.php
index 4b0b537b801f..d448962cb55a 100644
--- a/user_guide_src/source/incoming/request/003.php
+++ b/user_guide_src/source/incoming/request/003.php
@@ -1,5 +1,3 @@
 <?php
 
-echo $request->getMethod(true);  // Outputs: POST
-echo $request->getMethod(false); // Outputs: post
-echo $request->getMethod();      // Outputs: post
+echo $request->getMethod(); // Outputs: POST
diff --git a/user_guide_src/source/incoming/routing/004.php b/user_guide_src/source/incoming/routing/004.php
index a071f75cd156..d7b211c8d81b 100644
--- a/user_guide_src/source/incoming/routing/004.php
+++ b/user_guide_src/source/incoming/routing/004.php
@@ -1,3 +1,3 @@
 <?php
 
-$routes->match(['get', 'put'], 'products', 'Product::feature');
+$routes->match(['GET', 'PUT'], 'products', 'Product::feature');
diff --git a/user_guide_src/source/incoming/routing/033.php b/user_guide_src/source/incoming/routing/033.php
index ff7e995a1526..1f2892fc3f0f 100644
--- a/user_guide_src/source/incoming/routing/033.php
+++ b/user_guide_src/source/incoming/routing/033.php
@@ -8,7 +8,7 @@
 $routes->options('from', 'to', $options);
 $routes->delete('from', 'to', $options);
 $routes->patch('from', 'to', $options);
-$routes->match(['get', 'put'], 'from', 'to', $options);
+$routes->match(['GET', 'PUT'], 'from', 'to', $options);
 $routes->resource('photos', $options);
 $routes->map($array, $options);
 $routes->group('name', $options, static function () {});
diff --git a/user_guide_src/source/installation/upgrade_415/001.php b/user_guide_src/source/installation/upgrade_415/001.php
index 9d51911e38eb..272f9e2f1fab 100644
--- a/user_guide_src/source/installation/upgrade_415/001.php
+++ b/user_guide_src/source/installation/upgrade_415/001.php
@@ -9,8 +9,8 @@ class Filters extends BaseConfig
     // ...
 
     public $methods = [
-        'get'  => ['csrf'],
-        'post' => ['csrf'],
+        'GET'  => ['csrf'],
+        'POST' => ['csrf'],
     ];
     // ...
 }
diff --git a/user_guide_src/source/installation/upgrade_450.rst b/user_guide_src/source/installation/upgrade_450.rst
index 04607dde6489..6f756d0f8f7e 100644
--- a/user_guide_src/source/installation/upgrade_450.rst
+++ b/user_guide_src/source/installation/upgrade_450.rst
@@ -18,6 +18,58 @@ Mandatory File Changes
 Breaking Changes
 ****************
 
+.. _upgrade-450-lowercase-http-method-name:
+
+Lowercase HTTP Method Name
+==========================
+
+Request::getMethod()
+--------------------
+
+For historical reasons, ``Request::getMethod()`` returned HTTP method names in
+lower case by default.
+
+But the method token is case-sensitive because it might be used as a gateway
+to object-based systems with case-sensitive method names. By convention,
+standardized methods are defined in all-uppercase US-ASCII letters.
+See https://www.rfc-editor.org/rfc/rfc9110#name-overview.
+
+Now the deprecated ``$upper`` parameter in ``Request::getMethod()`` has been
+removed, and the ``getMethod()`` returns the as-is HTTP method name. That is,
+uppercase like "GET", "POST", and so on.
+
+If you want lowercase HTTP method names, use PHP's ``strtolower()`` function::
+
+    strtolower($request->getMethod())
+
+And you should use uppercase HTTP method names in your app code.
+
+app/Config/Filters.php
+----------------------
+
+You should update the keys in ``$methods`` in **app/Config/Filters.php**::
+
+    public array $methods = [
+        'POST' => ['invalidchars', 'csrf'],
+        'GET'  => ['csrf'],
+    ];
+
+CURLRequest::request()
+----------------------
+
+In previous versions, you could pass lowercase HTTP methods to the ``request()``
+method. But this bug has been fixed.
+
+Now you must pass the correct HTTP method names like "GET", "POST". Otherwise
+you would get the error response::
+
+    $client   = \Config\Services::curlrequest();
+    $response = $client->request('get', 'https://www.google.com/', [
+        'http_errors' => false,
+    ]);
+    $response->getStatusCode(); // In previous versions: 200
+                                //     In this verrsion: 405
+
 .. _upgrade-450-nested-route-groups-and-options:
 
 Nested Route Groups and Options
diff --git a/user_guide_src/source/installation/upgrade_4xx.rst b/user_guide_src/source/installation/upgrade_4xx.rst
index 4ead169d1592..70aa534274cf 100644
--- a/user_guide_src/source/installation/upgrade_4xx.rst
+++ b/user_guide_src/source/installation/upgrade_4xx.rst
@@ -92,6 +92,19 @@ Model, View and Controller
     upgrade_views
     upgrade_controllers
 
+Core Class Changes
+==================
+
+- Input
+    - CI3's `Input <http://codeigniter.com/userguide3/libraries/input.html>`_
+      corresponds to CI4's :doc:`IncomingRequest </incoming/incomingrequest>`.
+    - For historical reasons, CI3 and CI4 used incorrect HTTP method names like
+      "get", "post". Since v4.5.0, CI4 uses the correct HTTP method names like
+      "GET", "POST".
+- Output
+    - CI3's `Output <http://codeigniter.com/userguide3/libraries/output.html>`_
+      corresponds to CI4's :doc:`Responses </outgoing/response>`.
+
 Class Loading
 =============
 
@@ -194,8 +207,6 @@ Upgrading Libraries
   `Trackback <http://codeigniter.com/userguide3/libraries/trackback.html>`_,
   `XML-RPC /-Server <http://codeigniter.com/userguide3/libraries/xmlrpc.html>`_,
   and `Zip Encoding <http://codeigniter.com/userguide3/libraries/zip.html>`_.
-- CI3's `Input <http://codeigniter.com/userguide3/libraries/input.html>`_ corresponds to CI4's :doc:`IncomingRequest </incoming/incomingrequest>`.
-- CI3's `Output <http://codeigniter.com/userguide3/libraries/output.html>`_ corresponds to CI4's :doc:`Responses </outgoing/response>`.
 - All the other libraries, which exist in both CodeIgniter versions, can be upgraded with some adjustments.
   The most important and mostly used libraries received an Upgrade Guide, which will help you with simple
   steps and examples to adjust your code.
diff --git a/user_guide_src/source/libraries/curlrequest/017.php b/user_guide_src/source/libraries/curlrequest/017.php
index 3f6012cfb70b..c88ba46b553b 100644
--- a/user_guide_src/source/libraries/curlrequest/017.php
+++ b/user_guide_src/source/libraries/curlrequest/017.php
@@ -1,3 +1,3 @@
 <?php
 
-$client->setBody($body)->request('put', 'http://example.com');
+$client->setBody($body)->request('PUT', 'http://example.com');
diff --git a/user_guide_src/source/libraries/curlrequest/018.php b/user_guide_src/source/libraries/curlrequest/018.php
index 16fba53e2e8b..739784bc8152 100644
--- a/user_guide_src/source/libraries/curlrequest/018.php
+++ b/user_guide_src/source/libraries/curlrequest/018.php
@@ -1,3 +1,3 @@
 <?php
 
-$client->request('put', 'http://example.com', ['body' => $body]);
+$client->request('PUT', 'http://example.com', ['body' => $body]);
diff --git a/user_guide_src/source/libraries/curlrequest/019.php b/user_guide_src/source/libraries/curlrequest/019.php
index 0382d08e1bbc..9c74dd29ca58 100644
--- a/user_guide_src/source/libraries/curlrequest/019.php
+++ b/user_guide_src/source/libraries/curlrequest/019.php
@@ -1,3 +1,3 @@
 <?php
 
-$client->request('get', '/', ['cert' => ['/path/server.pem', 'password']]);
+$client->request('GET', '/', ['cert' => ['/path/server.pem', 'password']]);
diff --git a/user_guide_src/source/libraries/curlrequest/025.php b/user_guide_src/source/libraries/curlrequest/025.php
index acc8b40002ef..5f1818a7fe0b 100644
--- a/user_guide_src/source/libraries/curlrequest/025.php
+++ b/user_guide_src/source/libraries/curlrequest/025.php
@@ -1,6 +1,6 @@
 <?php
 
-$client->request('get', '/', [
+$client->request('GET', '/', [
     'headers' => [
         'User-Agent' => 'testing/1.0',
         'Accept'     => 'application/json',
diff --git a/user_guide_src/source/libraries/security/009.php b/user_guide_src/source/libraries/security/009.php
index bd6bc93cfeb6..fb9d114b026e 100644
--- a/user_guide_src/source/libraries/security/009.php
+++ b/user_guide_src/source/libraries/security/009.php
@@ -7,8 +7,8 @@
 class Filters extends BaseConfig
 {
     public $methods = [
-        'get'  => ['csrf'],
-        'post' => ['csrf'],
+        'GET'  => ['csrf'],
+        'POST' => ['csrf'],
     ];
 
     // ...
diff --git a/user_guide_src/source/libraries/throttler/004.php b/user_guide_src/source/libraries/throttler/004.php
index ab4d91257f8f..246b034d035e 100644
--- a/user_guide_src/source/libraries/throttler/004.php
+++ b/user_guide_src/source/libraries/throttler/004.php
@@ -7,7 +7,7 @@
 class Filters extends BaseConfig
 {
     public $methods = [
-        'post' => ['throttle'],
+        'POST' => ['throttle'],
     ];
 
     // ...
diff --git a/user_guide_src/source/testing/feature/002.php b/user_guide_src/source/testing/feature/002.php
index 8af5fda7b7c6..a47406b24aeb 100644
--- a/user_guide_src/source/testing/feature/002.php
+++ b/user_guide_src/source/testing/feature/002.php
@@ -1,7 +1,7 @@
 <?php
 
 // Get a simple page
-$result = $this->call('get', '/');
+$result = $this->call('GET', '/');
 
 // Submit a form
 $result = $this->call('post', 'contact', [
diff --git a/user_guide_src/source/testing/feature/004.php b/user_guide_src/source/testing/feature/004.php
index 4f98ced2f8d6..7e9a45d71c33 100644
--- a/user_guide_src/source/testing/feature/004.php
+++ b/user_guide_src/source/testing/feature/004.php
@@ -1,7 +1,7 @@
 <?php
 
 $routes = [
-    ['get', 'users', 'UserController::list'],
+    ['GET', 'users', 'UserController::list'],
 ];
 
 $result = $this->withRoutes($routes)->get('users');
diff --git a/user_guide_src/source/tutorial/create_news_items/001.php b/user_guide_src/source/tutorial/create_news_items/001.php
index 8c5ce7508349..3fc800af1a22 100644
--- a/user_guide_src/source/tutorial/create_news_items/001.php
+++ b/user_guide_src/source/tutorial/create_news_items/001.php
@@ -9,7 +9,7 @@ class Filters extends BaseConfig
     // ...
 
     public $methods = [
-        'post' => ['csrf'],
+        'POST' => ['csrf'],
     ];
 
     // ...