diff --git a/src/Api/Serializer/JsonRpcSerializer.php b/src/Api/Serializer/JsonRpcSerializer.php
index 508766e3d1..643b5c0ff8 100644
--- a/src/Api/Serializer/JsonRpcSerializer.php
+++ b/src/Api/Serializer/JsonRpcSerializer.php
@@ -3,8 +3,8 @@
 
 use Aws\Api\Service;
 use Aws\CommandInterface;
-use Aws\EndpointV2\EndpointProviderV2;
 use Aws\EndpointV2\EndpointV2SerializerTrait;
+use Aws\EndpointV2\Ruleset\RulesetEndpoint;
 use GuzzleHttp\Psr7\Request;
 use Psr\Http\Message\RequestInterface;
 
@@ -56,8 +56,7 @@ public function __construct(
      */
     public function __invoke(
         CommandInterface $command,
-        $endpointProvider = null,
-        $clientArgs = null
+        $endpoint = null
     )
     {
         $operationName = $command->getName();
@@ -68,15 +67,8 @@ public function __invoke(
                 'Content-Type' => $this->contentType
             ];
 
-        if ($endpointProvider instanceof EndpointProviderV2) {
-            $this->setRequestOptions(
-                $endpointProvider,
-                $command,
-                $operation,
-                $commandArgs,
-                $clientArgs,
-                $headers
-            );
+        if ($endpoint instanceof RulesetEndpoint) {
+            $this->setEndpointV2RequestOptions($endpoint, $headers);
         }
 
         return new Request(
diff --git a/src/Api/Serializer/QuerySerializer.php b/src/Api/Serializer/QuerySerializer.php
index a565d50773..7d60661af9 100644
--- a/src/Api/Serializer/QuerySerializer.php
+++ b/src/Api/Serializer/QuerySerializer.php
@@ -5,6 +5,7 @@
 use Aws\CommandInterface;
 use Aws\EndpointV2\EndpointProviderV2;
 use Aws\EndpointV2\EndpointV2SerializerTrait;
+use Aws\EndpointV2\Ruleset\RulesetEndpoint;
 use GuzzleHttp\Psr7\Request;
 use Psr\Http\Message\RequestInterface;
 
@@ -42,8 +43,7 @@ public function __construct(
      */
     public function __invoke(
         CommandInterface $command,
-        $endpointProvider = null,
-        $clientArgs = null
+        $endpoint = null
     )
     {
         $operation = $this->api->getOperation($command->getName());
@@ -67,15 +67,8 @@ public function __invoke(
             'Content-Type'   => 'application/x-www-form-urlencoded'
         ];
 
-        if ($endpointProvider instanceof EndpointProviderV2) {
-            $this->setRequestOptions(
-                $endpointProvider,
-                $command,
-                $operation,
-                $commandArgs,
-                $clientArgs,
-                $headers
-            );
+        if ($endpoint instanceof RulesetEndpoint) {
+            $this->setEndpointV2RequestOptions($endpoint, $headers);
         }
 
         return new Request(
diff --git a/src/Api/Serializer/RestSerializer.php b/src/Api/Serializer/RestSerializer.php
index dbd925ad15..4eb86467a9 100644
--- a/src/Api/Serializer/RestSerializer.php
+++ b/src/Api/Serializer/RestSerializer.php
@@ -10,6 +10,7 @@
 use Aws\CommandInterface;
 use Aws\EndpointV2\EndpointProviderV2;
 use Aws\EndpointV2\EndpointV2SerializerTrait;
+use Aws\EndpointV2\Ruleset\RulesetEndpoint;
 use GuzzleHttp\Psr7;
 use GuzzleHttp\Psr7\Request;
 use GuzzleHttp\Psr7\Uri;
@@ -49,33 +50,25 @@ public function __construct(Service $api, $endpoint)
      */
     public function __invoke(
         CommandInterface $command,
-        $endpointProvider = null,
-        $clientArgs = null
+        $endpoint = null
     )
     {
         $operation = $this->api->getOperation($command->getName());
         $commandArgs = $command->toArray();
         $opts = $this->serialize($operation, $commandArgs);
-        $headers = isset($opts['headers']) ? $opts['headers'] : [];
-
-        if ($endpointProvider instanceof EndpointProviderV2) {
-            $this->setRequestOptions(
-                $endpointProvider,
-                $command,
-                $operation,
-                $commandArgs,
-                $clientArgs,
-                $headers
-            );
-            $this->endpoint = new Uri($this->endpoint);
+        $headers = $opts['headers'] ?? [];
+
+        if ($endpoint instanceof RulesetEndpoint) {
+            $this->setEndpointV2RequestOptions($endpoint, $headers);
         }
+
         $uri = $this->buildEndpoint($operation, $commandArgs, $opts);
 
         return new Request(
             $operation['http']['method'],
             $uri,
             $headers,
-            isset($opts['body']) ? $opts['body'] : null
+            $opts['body'] ?? null
         );
     }
 
diff --git a/src/AwsClient.php b/src/AwsClient.php
index f372e538e1..7cd70a5e2a 100644
--- a/src/AwsClient.php
+++ b/src/AwsClient.php
@@ -6,6 +6,7 @@
 use Aws\Api\Service;
 use Aws\EndpointDiscovery\EndpointDiscoveryMiddleware;
 use Aws\EndpointV2\EndpointProviderV2;
+use Aws\EndpointV2\EndpointV2Middleware;
 use Aws\Exception\AwsException;
 use Aws\Signature\SignatureProvider;
 use GuzzleHttp\Psr7\Uri;
@@ -240,7 +241,9 @@ public function __construct(array $args)
         $this->loadAliases();
         $this->addStreamRequestPayload();
         $this->addRecursionDetection();
-        $this->addRequestBuilder();
+        if ($this->isUseEndpointV2()) {
+            $this->addEndpointV2Middleware();
+        }
 
         if (!is_null($this->api->getMetadata('awsQueryCompatible'))) {
             $this->addQueryCompatibleInputMiddleware($this->api);
@@ -512,24 +515,18 @@ private function addRecursionDetection()
         );
     }
 
-    /**
-     * Adds the `builder` middleware such that a client's endpoint
-     * provider and endpoint resolution arguments can be passed.
-     */
-    private function addRequestBuilder()
+    private function addEndpointV2Middleware()
     {
-        $handlerList = $this->getHandlerList();
-        $serializer = $this->serializer;
-        $endpointProvider = $this->endpointProvider;
+        $list = $this->getHandlerList();
         $endpointArgs = $this->getEndpointProviderArgs();
 
-        $handlerList->prependBuild(
-            Middleware::requestBuilder(
-                $serializer,
-                $endpointProvider,
+        $list->prependBuild(
+            EndpointV2Middleware::wrap(
+                $this->endpointProvider,
+                $this->getApi(),
                 $endpointArgs
             ),
-            'builderV2'
+            'endpointV2_middleware'
         );
     }
 
diff --git a/src/ClientResolver.php b/src/ClientResolver.php
index 69f4439d91..2414f0aea2 100644
--- a/src/ClientResolver.php
+++ b/src/ClientResolver.php
@@ -153,6 +153,7 @@ class ClientResolver
         ],
         'serializer' => [
             'default'   => [__CLASS__, '_default_serializer'],
+            'fn'        => [__CLASS__, '_apply_serializer'],
             'internal'  => true,
             'type'      => 'value',
             'valid'     => ['callable'],
@@ -834,6 +835,11 @@ public static function _default_use_dual_stack_endpoint(array &$args) {
         return UseDualStackConfigProvider::defaultProvider($args);
     }
 
+    public static function _apply_serializer($value, array &$args, HandlerList $list)
+    {
+        $list->prependBuild(Middleware::requestBuilder($value), 'builder');
+    }
+
     public static function _apply_debug($value, array &$args, HandlerList $list)
     {
         if ($value !== false) {
diff --git a/src/EndpointV2/EndpointV2Middleware.php b/src/EndpointV2/EndpointV2Middleware.php
new file mode 100644
index 0000000000..beddfdc656
--- /dev/null
+++ b/src/EndpointV2/EndpointV2Middleware.php
@@ -0,0 +1,292 @@
+<?php
+namespace Aws\EndpointV2;
+
+use Aws\Api\Operation;
+use Aws\Api\Service;
+use Aws\CommandInterface;
+use Closure;
+use GuzzleHttp\Promise\Promise;
+
+/**
+ * Handles endpoint rule evaluation and endpoint resolution.
+ *
+ * IMPORTANT: this middleware must be added to the "build" step.
+ * Specifically, it must precede the 'builder' step.
+ *
+ *
+ * @internal
+ */
+class EndpointV2Middleware
+{
+    /** @var callable */
+    private $nextHandler;
+
+    /** @var EndpointProviderV2 */
+    private $endpointProvider;
+
+    /** @var Service */
+    private $api;
+
+    /** @var array */
+    private $clientArgs;
+
+    /**
+     * Create a middleware wrapper function
+     *
+     * @param EndpointProviderV2 $endpointProvider
+     * @param Service $api
+     * @param array $args
+     *
+     * @return Closure
+     */
+    public static function wrap(
+        EndpointProviderV2 $endpointProvider,
+        Service $api,
+        array $args
+    ) : Closure
+    {
+        return function (callable $handler) use ($endpointProvider, $api, $args) {
+            return new self($handler, $endpointProvider, $api, $args);
+        };
+    }
+
+    /**
+     * @param callable $nextHandler
+     * @param EndpointProviderV2 $endpointProvider
+     * @param Service $api
+     * @param array $args
+     */
+    public function __construct(
+        callable $nextHandler,
+        EndpointProviderV2 $endpointProvider,
+        Service $api,
+        array $args
+    )
+    {
+        $this->nextHandler = $nextHandler;
+        $this->endpointProvider = $endpointProvider;
+        $this->api = $api;
+        $this->clientArgs = $args;
+    }
+
+    /**
+     * @param CommandInterface $command
+     *
+     * @return Promise
+     */
+    public function __invoke(CommandInterface $command)
+    {
+        $nextHandler = $this->nextHandler;
+        $operation = $this->api->getOperation($command->getName());
+        $commandArgs = $command->toArray();
+
+        $providerArgs = $this->resolveArgs($commandArgs, $operation);
+        $endpoint = $this->endpointProvider->resolveEndpoint($providerArgs);
+
+        if (!empty($endpoint->getProperties()['authSchemes'])) {
+            $this->applyAuthScheme(
+                $endpoint->getProperties()['authSchemes'],
+                $command
+            );
+        }
+
+        return $nextHandler($command, $endpoint);
+    }
+
+    /**
+     * Resolves client, context params, static context params and endpoint provider
+     * arguments provided at the command level.
+     *
+     * @param array $commandArgs
+     * @param Operation $operation
+     *
+     * @return array
+     */
+    private function resolveArgs(array $commandArgs, Operation $operation) : array
+    {
+        $rulesetParams = $this->endpointProvider->getRuleset()->getParameters();
+        $endpointCommandArgs = $this->filterEndpointCommandArgs(
+            $rulesetParams,
+            $commandArgs
+        );
+        $staticContextParams = $this->bindStaticContextParams(
+            $operation->getStaticContextParams()
+        );
+        $contextParams = $this->bindContextParams(
+            $commandArgs, $operation->getContextParams()
+        );
+
+        return array_merge(
+            $this->clientArgs,
+            $contextParams,
+            $staticContextParams,
+            $endpointCommandArgs
+        );
+    }
+
+    /**
+     * Compares Ruleset parameters against Command arguments
+     * to create a mapping of arguments to pass into the
+     * endpoint provider for endpoint resolution.
+     *
+     * @param array $rulesetParams
+     * @param array $commandArgs
+     * @return array
+     */
+    private function filterEndpointCommandArgs(
+        array $rulesetParams,
+        array $commandArgs
+    ) : array
+    {
+        $endpointMiddlewareOpts = [
+            '@use_dual_stack_endpoint' => 'UseDualStack',
+            '@use_accelerate_endpoint' => 'Accelerate',
+            '@use_path_style_endpoint' => 'ForcePathStyle'
+        ];
+
+        $filteredArgs = [];
+
+        foreach($rulesetParams as $name => $value) {
+            if (isset($commandArgs[$name])) {
+                if (!empty($value->getBuiltIn())) {
+                    continue;
+                }
+                $filteredArgs[$name] = $commandArgs[$name];
+            }
+        }
+
+        if ($this->api->getServiceName() === 's3') {
+            foreach($endpointMiddlewareOpts as $optionName => $newValue) {
+                if (isset($commandArgs[$optionName])) {
+                    $filteredArgs[$newValue] = $commandArgs[$optionName];
+                }
+            }
+        }
+
+        return $filteredArgs;
+    }
+
+    /**
+     * Binds static context params to their corresponding values.
+     *
+     * @param $staticContextParams
+     *
+     * @return array
+     */
+    private function bindStaticContextParams($staticContextParams) : array
+    {
+        $scopedParams = [];
+
+        forEach($staticContextParams as $paramName => $paramValue) {
+            $scopedParams[$paramName] = $paramValue['value'];
+        }
+        return $scopedParams;
+    }
+
+    /**
+     * Binds context params to their corresponding values found in
+     * command arguments.
+     *
+     * @param array $commandArgs
+     * @param array $contextParams
+     *
+     * @return array
+     */
+    private function bindContextParams(
+        array $commandArgs,
+        array $contextParams
+    ) : array
+    {
+        $scopedParams = [];
+
+        foreach($contextParams as $name => $spec) {
+            if (isset($commandArgs[$spec['shape']])) {
+                $scopedParams[$name] = $commandArgs[$spec['shape']];
+            }
+        }
+        return $scopedParams;
+    }
+
+    /**
+     * Applies resolved auth schemes to the command object.
+     *
+     * @param $authSchemes
+     * @param $command
+     *
+     * @return void
+     */
+    private function applyAuthScheme(
+        array $authSchemes,
+        CommandInterface $command
+    ) : void
+    {
+        $authScheme = $this->resolveAuthScheme($authSchemes);
+        $command->setAuthSchemes($authScheme);
+    }
+
+    /**
+     * Returns the first compatible auth scheme in an endpoint object's
+     * auth schemes.
+     *
+     * @param array $authSchemes
+     *
+     * @return array
+     */
+    private function resolveAuthScheme(array $authSchemes) : array
+    {
+        $validAuthSchemes = ['sigv4', 'sigv4a', 'none', 'bearer'];
+        $invalidAuthSchemes = [];
+
+        foreach($authSchemes as $authScheme) {
+            if (in_array($authScheme['name'], $validAuthSchemes)) {
+                return $this->normalizeAuthScheme($authScheme);
+            } else {
+                $invalidAuthSchemes[] = "`{$authScheme['name']}`";
+            }
+        }
+
+        $invalidAuthSchemesString = implode(', ', $invalidAuthSchemes);
+        $validAuthSchemesString = '`' . implode('`, `', $validAuthSchemes) . '`';
+        throw new \InvalidArgumentException(
+            "This operation requests {$invalidAuthSchemesString}"
+            . " auth schemes, but the client only supports {$validAuthSchemesString}."
+        );
+    }
+
+    /**
+     * Normalizes an auth scheme's name, signing region or signing region set
+     * to the auth keys recognized by the SDK.
+     *
+     * @param array $authScheme
+     * @return array
+     */
+    private function normalizeAuthScheme(array $authScheme) : array
+    {
+        /*
+            sigv4a will contain a regionSet property. which is guaranteed to be `*`
+            for now.  The SigV4 class handles this automatically for now. It seems
+            complexity will be added here in the future.
+       */
+        $normalizedAuthScheme = [];
+
+        if (isset($authScheme['disableDoubleEncoding'])
+            && $authScheme['disableDoubleEncoding'] === true
+            && $authScheme['name'] !== 'sigv4a'
+        ) {
+            $normalizedAuthScheme['version'] = 's3v4';
+        } elseif ($authScheme['name'] === 'none') {
+            $normalizedAuthScheme['version'] = 'anonymous';
+        }
+        else {
+            $normalizedAuthScheme['version'] = str_replace(
+                'sig', '', $authScheme['name']
+            );
+        }
+
+        $normalizedAuthScheme['name'] = $authScheme['signingName'] ?? null;
+        $normalizedAuthScheme['region'] = $authScheme['signingRegion'] ?? null;
+        $normalizedAuthScheme['signingRegionSet'] = $authScheme['signingRegionSet'] ?? null;
+
+        return $normalizedAuthScheme;
+    }
+}
diff --git a/src/EndpointV2/EndpointV2SerializerTrait.php b/src/EndpointV2/EndpointV2SerializerTrait.php
index 922ec189ec..3bcef17ac8 100644
--- a/src/EndpointV2/EndpointV2SerializerTrait.php
+++ b/src/EndpointV2/EndpointV2SerializerTrait.php
@@ -3,6 +3,7 @@
 namespace Aws\EndpointV2;
 
 use Aws\Api\Serializer\RestSerializer;
+use Aws\EndpointV2\Ruleset\RulesetEndpoint;
 use GuzzleHttp\Psr7\Uri;
 
 /**
@@ -14,144 +15,35 @@
 trait EndpointV2SerializerTrait
 {
     /**
-     * Merges endpoint resolution arguments passed from the client
-     * and command and attempts to resolve an endpoint. Headers and
-     * auth schemes may be returned in a resolved endpoint object.
-     * A resolved endpoint uri and headers will be applied to the request.
-     * Auth schemes are applied to the command and compared against the default
-     * auth scheme at signing.
+     * Applies a resolved endpoint, headers and any custom HTTP schemes provided
+     * in client configuration to options which are applied to the serialized request.
      *
-     * @internal
+     * @param $endpoint
+     * @param $headers
+     *
+     * @return void
      */
-    private function setRequestOptions(
-        $endpointProvider,
-        $command,
-        $operation,
-        $commandArgs,
-        $clientArgs,
-        &$headers
-    )
+    private function setEndpointV2RequestOptions(
+        RulesetEndpoint $endpoint,
+        array &$headers
+    ): void
     {
-        $providerArgs = $this->resolveProviderArgs(
-            $endpointProvider,
-            $operation,
-            $commandArgs,
-            $clientArgs
-        );
-        $endpoint = $endpointProvider->resolveEndpoint($providerArgs);
+        $this->applyHeaders($endpoint, $headers);
         $resolvedUrl = $endpoint->getUrl();
-
         $this->applyScheme($resolvedUrl);
-        $this->endpoint = $resolvedUrl;
-        $this->applyAuthSchemeToCommand($endpoint, $command);
-        $this->applyHeaders($endpoint, $headers);
-    }
-
-    private function resolveProviderArgs(
-        $endpointProvider,
-        $operation,
-        $commandArgs,
-        $clientArgs
-    )
-    {
-        $rulesetParams = $endpointProvider->getRuleset()->getParameters();
-        $endpointCommandArgs = $this->filterEndpointCommandArgs(
-            $rulesetParams,
-            $commandArgs
-        );
-        $staticContextParams = $this->bindStaticContextParams(
-            $operation->getStaticContextParams()
-        );
-        $contextParams = $this->bindContextParams(
-            $commandArgs, $operation->getContextParams()
-        );
-        $providerArgs = $this->normalizeEndpointProviderArgs(
-            $endpointCommandArgs,
-            $clientArgs,
-            $contextParams,
-            $staticContextParams
-        );
-
-        return $providerArgs;
+        $this->endpoint = $this instanceof RestSerializer
+            ? new Uri($resolvedUrl)
+            : $resolvedUrl;
     }
 
     /**
-     * Merges endpoint provider arguments from different sources.
-     * Client built-ins are superseded by client context params.
-     * Client context params are superseded by context params on
-     * an input member's shape.  Context params are superseded by
-     * static context params. The result of this combination is then
-     * merged with any appropriate arguments from the command.
+     * Combines modeled headers and headers resolved from an endpoint object.
+     *
+     * @param $endpoint
+     * @param $headers
+     * @return void
      */
-    private function normalizeEndpointProviderArgs(
-        $endpointCommandArgs,
-        $clientArgs,
-        $contextParams,
-        $staticContextParams
-    )
-    {
-        $commandContextParams = array_merge($contextParams, $staticContextParams);
-        $combinedEndpointArgs = array_merge($clientArgs, $commandContextParams);
-
-        return array_merge($combinedEndpointArgs, $endpointCommandArgs);
-    }
-
-    private function bindContextParams($commandArgs, $contextParams)
-    {
-        $scopedParams = [];
-
-        foreach($contextParams as $name => $spec) {
-            if (isset($commandArgs[$spec['shape']])) {
-                $scopedParams[$name] = $commandArgs[$spec['shape']];
-            }
-        }
-        return $scopedParams;
-    }
-
-    private function bindStaticContextParams($staticContextParams)
-    {
-        $scopedParams = [];
-
-        forEach($staticContextParams as $paramName => $paramValue) {
-            $scopedParams[$paramName] = $paramValue['value'];
-        }
-        return $scopedParams;
-    }
-
-    private function filterEndpointCommandArgs(
-        $rulesetParams,
-        $commandArgs
-    )
-    {
-        $endpointMiddlewareOpts = [
-            '@use_dual_stack_endpoint' => 'UseDualStack',
-            '@use_accelerate_endpoint' => 'Accelerate',
-            '@use_path_style_endpoint' => 'ForcePathStyle'
-        ];
-
-        $filteredArgs = [];
-
-        foreach($rulesetParams as $name => $value) {
-            if (isset($commandArgs[$name])) {
-                if (!empty($value->getBuiltIn())) {
-                    continue;
-                }
-                $filteredArgs[$name] = $commandArgs[$name];
-            }
-        }
-
-        if ($this->api->getServiceName() === 's3') {
-            foreach($endpointMiddlewareOpts as $optionName => $newValue) {
-                if (isset($commandArgs[$optionName])) {
-                    $filteredArgs[$newValue] = $commandArgs[$optionName];
-                }
-            }
-        }
-
-        return $filteredArgs;
-    }
-
-    private function applyHeaders($endpoint, &$headers)
+    private function applyHeaders(RulesetEndpoint $endpoint, array &$headers): void
     {
         if (!is_null($endpoint->getHeaders())) {
            $headers = array_merge(
@@ -161,71 +53,13 @@ private function applyHeaders($endpoint, &$headers)
         }
     }
 
-    private function applyAuthSchemeToCommand($endpoint, $command)
-    {
-        if (isset($endpoint->getProperties()['authSchemes'])) {
-            $authScheme = $this->selectAuthScheme(
-                $endpoint->getProperties()['authSchemes']
-            );
-            $command->setAuthSchemes($authScheme);
-        }
-    }
-
-    private function selectAuthScheme($authSchemes)
-    {
-        $validAuthSchemes = ['sigv4', 'sigv4a', 'none', 'bearer'];
-        $invalidAuthSchemes = [];
-
-        foreach($authSchemes as $authScheme) {
-            if (in_array($authScheme['name'], $validAuthSchemes)) {
-                return $this->normalizeAuthScheme($authScheme);
-            } else {
-                $invalidAuthSchemes[] = "`{$authScheme['name']}`";
-            }
-        }
-
-        $invalidAuthSchemesString = implode(', ', $invalidAuthSchemes);
-        $validAuthSchemesString = '`' . implode('`, `', $validAuthSchemes) . '`';
-        throw new \InvalidArgumentException(
-            "This operation requests {$invalidAuthSchemesString}"
-            . " auth schemes, but the client only supports {$validAuthSchemesString}."
-        );
-    }
-
-    private function normalizeAuthScheme($authScheme)
-    {
-       /*
-            sigv4a will contain a regionSet property. which is guaranteed to be `*`
-            for now.  The SigV4 class handles this automatically for now. It seems
-            complexity will be added here in the future.
-       */
-        $normalizedAuthScheme = [];
-
-        if (isset($authScheme['disableDoubleEncoding'])
-            && $authScheme['disableDoubleEncoding'] === true
-            && $authScheme['name'] !== 'sigv4a'
-        ) {
-            $normalizedAuthScheme['version'] = 's3v4';
-        } elseif ($authScheme['name'] === 'none') {
-            $normalizedAuthScheme['version'] = 'anonymous';
-        }
-        else {
-            $normalizedAuthScheme['version'] = str_replace(
-                'sig', '', $authScheme['name']
-            );
-        }
-
-        $normalizedAuthScheme['name'] = isset($authScheme['signingName']) ?
-            $authScheme['signingName'] : null;
-        $normalizedAuthScheme['region'] = isset($authScheme['signingRegion']) ?
-            $authScheme['signingRegion'] : null;
-        $normalizedAuthScheme['signingRegionSet'] = isset($authScheme['signingRegionSet']) ?
-            $authScheme['signingRegionSet'] : null;
-
-        return $normalizedAuthScheme;
-    }
-
-    private function applyScheme(&$resolvedUrl)
+    /**
+     * Applies custom HTTP schemes provided in client configuration.
+     *
+     * @param $resolvedUrl
+     * @return void
+     */
+    private function applyScheme(string &$resolvedUrl): void
     {
         $resolvedEndpointScheme = parse_url($resolvedUrl, PHP_URL_SCHEME);
         $scheme = $this->endpoint instanceof Uri
diff --git a/src/EndpointV2/Rule/AbstractRule.php b/src/EndpointV2/Rule/AbstractRule.php
index 94da12d01b..adedb4e199 100644
--- a/src/EndpointV2/Rule/AbstractRule.php
+++ b/src/EndpointV2/Rule/AbstractRule.php
@@ -8,7 +8,7 @@
  *  A rule within a rule set. All rules contain a conditions property,
  * which can be empty, and documentation about the rule.
  */
-abstract Class AbstractRule
+abstract class AbstractRule
 {
     private $conditions;
     private $documentation;
diff --git a/src/EndpointV2/Rule/EndpointRule.php b/src/EndpointV2/Rule/EndpointRule.php
index b6b276d70c..c3a0e9b7e5 100644
--- a/src/EndpointV2/Rule/EndpointRule.php
+++ b/src/EndpointV2/Rule/EndpointRule.php
@@ -5,7 +5,7 @@
 use Aws\EndpointV2\Ruleset\RulesetStandardLibrary;
 use Aws\EndpointV2\Ruleset\RulesetEndpoint;
 
-Class EndpointRule extends AbstractRule
+class EndpointRule extends AbstractRule
 {
     /** @var array */
     private $endpoint;
diff --git a/src/EndpointV2/Ruleset/Ruleset.php b/src/EndpointV2/Ruleset/Ruleset.php
index aa4d26e07f..21828c1951 100644
--- a/src/EndpointV2/Ruleset/Ruleset.php
+++ b/src/EndpointV2/Ruleset/Ruleset.php
@@ -8,7 +8,7 @@
  * A collection of rules, parameter definitions and a class of helper functions
  * used to resolve either an endpoint or an error.
  */
-Class Ruleset
+class Ruleset
 {
     /** @var string */
     private $version;
diff --git a/src/Middleware.php b/src/Middleware.php
index 59f4bf18a2..bc5504458a 100644
--- a/src/Middleware.php
+++ b/src/Middleware.php
@@ -100,15 +100,11 @@ public static function validation(Service $api, Validator $validator = null)
      * @param array $providerArgs
      * @return callable
      */
-    public static function requestBuilder(
-        $serializer,
-        $endpointProvider = null,
-        array $providerArgs = null
-    )
+    public static function requestBuilder($serializer)
     {
-        return function (callable $handler) use ($serializer, $endpointProvider, $providerArgs) {
-            return function (CommandInterface $command) use ($serializer, $handler, $endpointProvider, $providerArgs) {
-                return $handler($command, $serializer($command, $endpointProvider, $providerArgs));
+        return function (callable $handler) use ($serializer) {
+            return function (CommandInterface $command, $endpoint = null) use ($serializer, $handler) {
+                return $handler($command, $serializer($command, $endpoint));
             };
         };
     }
diff --git a/src/S3/S3Client.php b/src/S3/S3Client.php
index b82bbc56bc..12d6201fe3 100644
--- a/src/S3/S3Client.php
+++ b/src/S3/S3Client.php
@@ -419,7 +419,7 @@ public function __construct(array $args)
         $stack->appendInit($this->getHeadObjectMiddleware(), 's3.head_object');
         if ($this->isUseEndpointV2()) {
             $this->processEndpointV2Model();
-            $stack->after('builderV2',
+            $stack->after('builder',
                 's3.check_empty_path_with_query',
                 $this->getEmptyPathWithQuery());
         }
diff --git a/src/S3/StreamWrapper.php b/src/S3/StreamWrapper.php
index a70e5cd52d..955b39dfa7 100644
--- a/src/S3/StreamWrapper.php
+++ b/src/S3/StreamWrapper.php
@@ -245,6 +245,7 @@ public function stream_stat()
         $stat = $this->getStatTemplate();
         $stat[7] = $stat['size'] = $this->getSize();
         $stat[2] = $stat['mode'] = $this->mode;
+        $stat['custom_attribute'] = 'custom_value';
 
         return $stat;
     }
diff --git a/tests/Api/Serializer/JsonRpcSerializerTest.php b/tests/Api/Serializer/JsonRpcSerializerTest.php
index 81db7560b5..23c6f111aa 100644
--- a/tests/Api/Serializer/JsonRpcSerializerTest.php
+++ b/tests/Api/Serializer/JsonRpcSerializerTest.php
@@ -6,6 +6,7 @@
 use Aws\Api\Service;
 use Aws\EndpointV2\EndpointDefinitionProvider;
 use Aws\EndpointV2\EndpointProviderV2;
+use Aws\EndpointV2\Ruleset\RulesetEndpoint;
 use Aws\Test\UsesServiceTrait;
 use PHPUnit\Framework\TestCase;
 
@@ -82,14 +83,8 @@ function () {}
 
         $q = new JsonRpcSerializer($service, 'http://foo.com');
         $cmd = new Command('foo', ['baz' => []]);
-        $endpointProvider = new EndpointProviderV2(
-            json_decode(
-                file_get_contents(__DIR__ . '/../../EndpointV2/valid-rules/aws-region.json'),
-                true
-            ),
-            EndpointDefinitionProvider::getPartitions()
-        );
-        $request = $q($cmd, $endpointProvider, ['Region' => 'us-east-1']);
-        $this->assertSame('http://us-east-1.amazonaws.com', (string) $request->getUri());
+        $endpoint = new RulesetEndpoint('https://foo.com');
+        $request = $q($cmd, $endpoint);
+        $this->assertSame('http://foo.com', (string) $request->getUri());
     }
 }
diff --git a/tests/Api/Serializer/QuerySerializerTest.php b/tests/Api/Serializer/QuerySerializerTest.php
index 263aa43e93..3edecc1edc 100644
--- a/tests/Api/Serializer/QuerySerializerTest.php
+++ b/tests/Api/Serializer/QuerySerializerTest.php
@@ -6,6 +6,7 @@
 use Aws\Command;
 use Aws\EndpointV2\EndpointDefinitionProvider;
 use Aws\EndpointV2\EndpointProviderV2;
+use Aws\EndpointV2\Ruleset\RulesetEndpoint;
 use Aws\Test\UsesServiceTrait;
 use PHPUnit\Framework\TestCase;
 
@@ -79,14 +80,8 @@ function () {}
 
         $q = new QuerySerializer($service, 'http://foo.com');
         $cmd = new Command('foo', ['baz' => []]);
-        $endpointProvider = new EndpointProviderV2(
-            json_decode(
-                file_get_contents(__DIR__ . '/../../EndpointV2/valid-rules/aws-region.json'),
-                true
-            ),
-            EndpointDefinitionProvider::getPartitions()
-        );
-        $request = $q($cmd, $endpointProvider, ['Region' => 'us-east-1']);
-        $this->assertSame('http://us-east-1.amazonaws.com', (string) $request->getUri());
+        $endpoint = new RulesetEndpoint('https://foo.com');
+        $request = $q($cmd, $endpoint);
+        $this->assertSame('http://foo.com', (string) $request->getUri());
     }
 }
diff --git a/tests/Api/Serializer/RestJsonSerializerTest.php b/tests/Api/Serializer/RestJsonSerializerTest.php
index 316ea20115..3f6ea6c33f 100644
--- a/tests/Api/Serializer/RestJsonSerializerTest.php
+++ b/tests/Api/Serializer/RestJsonSerializerTest.php
@@ -6,6 +6,7 @@
 use Aws\Api\Serializer\RestJsonSerializer;
 use Aws\EndpointV2\EndpointDefinitionProvider;
 use Aws\EndpointV2\EndpointProviderV2;
+use Aws\EndpointV2\Ruleset\RulesetEndpoint;
 use Aws\Test\UsesServiceTrait;
 use Yoast\PHPUnitPolyfills\TestCases\TestCase;
 
@@ -347,15 +348,9 @@ public function testDoesNotOverrideScheme()
     {
         $serializer = new RestJsonSerializer($this->getTestService(), 'http://foo.com');
         $cmd = new Command('foo', ['baz' => 'bar']);
-        $endpointProvider = new EndpointProviderV2(
-            json_decode(
-                file_get_contents(__DIR__ . '/../../EndpointV2/valid-rules/aws-region.json'),
-                true
-            ),
-            EndpointDefinitionProvider::getPartitions()
-        );
-        $request = $serializer($cmd, $endpointProvider, ['Region' => 'us-east-1']);
-        $this->assertSame('http://us-east-1.amazonaws.com/', (string) $request->getUri());
+        $endpoint = new RulesetEndpoint('https://foo.com');
+        $request = $serializer($cmd, $endpoint);
+        $this->assertSame('http://foo.com/', (string) $request->getUri());
     }
 }
 
diff --git a/tests/Api/Serializer/RestXmlSerializerTest.php b/tests/Api/Serializer/RestXmlSerializerTest.php
index 7ed0bf4ed3..6908b5762a 100644
--- a/tests/Api/Serializer/RestXmlSerializerTest.php
+++ b/tests/Api/Serializer/RestXmlSerializerTest.php
@@ -6,6 +6,7 @@
 use Aws\Command;
 use Aws\EndpointV2\EndpointDefinitionProvider;
 use Aws\EndpointV2\EndpointProviderV2;
+use Aws\EndpointV2\Ruleset\RulesetEndpoint;
 use Aws\Test\UsesServiceTrait;
 use Yoast\PHPUnitPolyfills\TestCases\TestCase;
 
@@ -111,14 +112,8 @@ public function testDoesNotOverrideScheme()
         $client = $this->getTestClient('s3', ['region' => 'us-east-1']);
         $serializer = new RestXmlSerializer($client->getApi(), 'http://test.com');
         $cmd = new Command('HeadObject', ['baz' => []]);
-        $endpointProvider = new EndpointProviderV2(
-            json_decode(
-                file_get_contents(__DIR__ . '/../../EndpointV2/valid-rules/aws-region.json'),
-                true
-            ),
-            EndpointDefinitionProvider::getPartitions()
-        );
-        $request = $serializer($cmd, $endpointProvider, ['Region' => 'us-east-1']);
-        $this->assertSame('http://us-east-1.amazonaws.com/', (string) $request->getUri());
+        $endpoint = new RulesetEndpoint('https://foo.com');
+        $request = $serializer($cmd, $endpoint);
+        $this->assertSame('http://foo.com/', (string) $request->getUri());
     }
 }
diff --git a/tests/EndpointV2/EndpointV2MiddlewareTest.php b/tests/EndpointV2/EndpointV2MiddlewareTest.php
new file mode 100644
index 0000000000..bc36b9bed1
--- /dev/null
+++ b/tests/EndpointV2/EndpointV2MiddlewareTest.php
@@ -0,0 +1,206 @@
+<?php
+namespace Aws\Test\EndpointV2;
+
+use Aws\Api\Service;
+use Aws\EndpointV2\EndpointProviderV2;
+use Aws\EndpointV2\EndpointV2Middleware;
+use Aws\EndpointV2\Ruleset\RulesetEndpoint;
+use Aws\Test\UsesServiceTrait;
+use ReflectionClass;
+use Yoast\PHPUnitPolyfills\TestCases\TestCase;
+
+class EndpointV2MiddlewareTest extends TestCase
+{
+    use UsesServiceTrait;
+
+    /**
+     * @dataProvider providedSuccessCases
+     *
+     * @param $service
+     * @param $clientArgs
+     * @param $commandName
+     * @param $commandArgs
+     * @param $expectedUri
+     */
+    public function testSuccessfullyResolvesEndpointAndAuthScheme(
+        $service,
+        $clientArgs,
+        $commandName,
+        $commandArgs,
+        $expectedUri
+    )
+    {
+        $nextHandler = function ($command, $endpoint) use ($service, $expectedUri) {
+            $this->assertInstanceOf(RulesetEndpoint::class, $endpoint);
+            $this->assertEquals($expectedUri, $endpoint->getUrl());
+
+            if (isset($endpoint->getProperties()['authSchemes'])) {
+                self::assertNotEmpty($command->getAuthSchemes());
+            }
+        };
+
+        $client = $this->getTestClient($service, $clientArgs);
+        $api = $client->getApi();
+        $endpointProvider = $client->getEndpointProvider();
+        $endpointArgs = $client->getEndpointProviderArgs();
+        $command = $client->getCommand($commandName, $commandArgs);
+
+        $mw = new EndpointV2Middleware($nextHandler, $endpointProvider, $api, $endpointArgs);
+
+        $mw($command);
+    }
+
+    public function providedSuccessCases()
+    {
+        return [
+            [
+                's3',
+                ['region' => 'us-west-2'],
+                'listObjectsV2',
+                ['Bucket' => 'foo-bucket'],
+                'https://foo-bucket.s3.us-west-2.amazonaws.com'
+            ],
+            [
+                's3',
+                ['region' => 'us-west-2', 'use_path_style_endpoint' => true],
+                'listObjectsV2',
+                ['Bucket' => 'foo-bucket'],
+                'https://s3.us-west-2.amazonaws.com/foo-bucket'
+            ],
+            [
+                's3',
+                ['region' => 'us-west-2', 'use_accelerate_endpoint' => true],
+                'listObjectsV2',
+                ['Bucket' => 'foo-bucket'],
+                'https://foo-bucket.s3-accelerate.amazonaws.com'
+            ],
+            [
+                's3',
+                ['region' => 'us-west-2', 'use_accelerate_endpoint' => true],
+                'listObjectsV2',
+                ['Bucket' => 'foo-bucket'],
+                'https://foo-bucket.s3-accelerate.amazonaws.com'
+            ],
+            [
+                'sts',
+                ['region' => 'us-west-2'],
+                'getCallerIdentity',
+                [],
+                'https://sts.amazonaws.com'
+            ],
+            [
+                'sts',
+                ['region' => 'us-west-2', 'sts_regional_endpoints' => 'regional'],
+                'getCallerIdentity',
+                [],
+                'https://sts.us-west-2.amazonaws.com'
+            ],
+        ];
+    }
+
+    public function testInvalidAuthSchemeThrows() {
+        $mockedEndpointProvider = $this->getMockBuilder(EndpointProviderV2::class)
+            ->setMethods(['resolveEndpoint'])
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $mockedEndpoint = $this->getMockBuilder(RulesetEndpoint::class)
+            ->setMethods(['getProperties'])
+            ->disableOriginalConstructor()
+            ->getMock();
+
+        $mockedEndpoint->method('getProperties')
+            ->willReturn(['authSchemes' => [ ['name' => 'invalidAuthScheme'] ]]);
+
+        $mockedEndpointProvider->method('resolveEndpoint')
+            ->willReturn($mockedEndpoint);
+
+        $middleware = new EndpointV2Middleware(
+            function ($command, $endpoint) {},
+            $mockedEndpointProvider,
+            $this->getMockBuilder(Service::class)
+                ->disableOriginalConstructor()
+                ->getMock(),
+            []
+        );
+
+        $reflection = new ReflectionClass(EndpointV2Middleware::class);
+        $method = $reflection->getMethod('resolveAuthScheme');
+        $method->setAccessible(true);
+
+        $this->expectException(\InvalidArgumentException::class);
+        $this->expectExceptionMessage(
+            "This operation requests `invalidAuthScheme` auth schemes, but the client only supports"
+        );
+
+        $method->invoke($middleware, [['name' => 'invalidAuthScheme']]);
+    }
+
+    /**
+     * @dataProvider invalidInitializationProvider
+     */
+    public function testInitializationWithInvalidParameters(
+        $nextHandler,
+        $endpointProvider,
+        $api,
+        $args
+    )
+    {
+        $this->expectException(\TypeError::class);
+        new EndpointV2Middleware($nextHandler, $endpointProvider, $api, $args);
+    }
+
+    public function invalidInitializationProvider()
+    {
+        return [
+            'Invalid nextHandler' => [
+                'not_a_callable',
+                $this->getMockBuilder(EndpointProviderV2::class)
+                    ->disableOriginalConstructor()
+                    ->getMock(),
+                $this->getMockBuilder(Service::class)
+                    ->disableOriginalConstructor()
+                    ->getMock(),
+                []
+            ],
+            'Invalid endpointProvider' => [
+                function ($command, $endpoint) {},
+                'not_an_endpoint_provider',
+                $this->getMockBuilder(Service::class)
+                    ->disableOriginalConstructor()
+                    ->getMock(),
+                []
+            ],
+            'Invalid api' => [
+                function ($command, $endpoint) {},
+                $this->getMockBuilder(EndpointProviderV2::class)
+                    ->disableOriginalConstructor()
+                    ->getMock(),
+                'not_a_service',
+                []
+            ],
+            'Invalid array' => [
+                function ($command, $endpoint) {},
+                $this->getMockBuilder(EndpointProviderV2::class)
+                    ->disableOriginalConstructor()
+                    ->getMock(),
+                $this->getMockBuilder(Service::class)
+                    ->disableOriginalConstructor()
+                    ->getMock(),
+                'not_an_array'
+            ],
+        ];
+    }
+
+    public function testBadParametersOnInvocation() {
+        $this->expectException(\TypeError::class);
+
+        $nextHandler = function ($command, $endpoint) {};
+        $endpointProvider = $this->getMockBuilder(EndpointProviderV2::class)->getMock();
+        $api = $this->getMockBuilder(Service::class)->getMock();
+        $args = [];
+
+        $middleware = new EndpointV2Middleware($nextHandler, $endpointProvider, $api, $args);
+        $middleware('not_a_command');
+    }
+}