diff --git a/src/Api/Serializer/JsonRpcSerializer.php b/src/Api/Serializer/JsonRpcSerializer.php
index 643b5c0ff8..508766e3d1 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;
 
@@ -56,7 +56,8 @@ public function __construct(
      */
     public function __invoke(
         CommandInterface $command,
-        $endpoint = null
+        $endpointProvider = null,
+        $clientArgs = null
     )
     {
         $operationName = $command->getName();
@@ -67,8 +68,15 @@ public function __invoke(
                 'Content-Type' => $this->contentType
             ];
 
-        if ($endpoint instanceof RulesetEndpoint) {
-            $this->setEndpointV2RequestOptions($endpoint, $headers);
+        if ($endpointProvider instanceof EndpointProviderV2) {
+            $this->setRequestOptions(
+                $endpointProvider,
+                $command,
+                $operation,
+                $commandArgs,
+                $clientArgs,
+                $headers
+            );
         }
 
         return new Request(
diff --git a/src/Api/Serializer/QuerySerializer.php b/src/Api/Serializer/QuerySerializer.php
index 7d60661af9..a565d50773 100644
--- a/src/Api/Serializer/QuerySerializer.php
+++ b/src/Api/Serializer/QuerySerializer.php
@@ -5,7 +5,6 @@
 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;
 
@@ -43,7 +42,8 @@ public function __construct(
      */
     public function __invoke(
         CommandInterface $command,
-        $endpoint = null
+        $endpointProvider = null,
+        $clientArgs = null
     )
     {
         $operation = $this->api->getOperation($command->getName());
@@ -67,8 +67,15 @@ public function __invoke(
             'Content-Type'   => 'application/x-www-form-urlencoded'
         ];
 
-        if ($endpoint instanceof RulesetEndpoint) {
-            $this->setEndpointV2RequestOptions($endpoint, $headers);
+        if ($endpointProvider instanceof EndpointProviderV2) {
+            $this->setRequestOptions(
+                $endpointProvider,
+                $command,
+                $operation,
+                $commandArgs,
+                $clientArgs,
+                $headers
+            );
         }
 
         return new Request(
diff --git a/src/Api/Serializer/RestSerializer.php b/src/Api/Serializer/RestSerializer.php
index 4eb86467a9..dbd925ad15 100644
--- a/src/Api/Serializer/RestSerializer.php
+++ b/src/Api/Serializer/RestSerializer.php
@@ -10,7 +10,6 @@
 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;
@@ -50,25 +49,33 @@ public function __construct(Service $api, $endpoint)
      */
     public function __invoke(
         CommandInterface $command,
-        $endpoint = null
+        $endpointProvider = null,
+        $clientArgs = null
     )
     {
         $operation = $this->api->getOperation($command->getName());
         $commandArgs = $command->toArray();
         $opts = $this->serialize($operation, $commandArgs);
-        $headers = $opts['headers'] ?? [];
-
-        if ($endpoint instanceof RulesetEndpoint) {
-            $this->setEndpointV2RequestOptions($endpoint, $headers);
+        $headers = isset($opts['headers']) ? $opts['headers'] : [];
+
+        if ($endpointProvider instanceof EndpointProviderV2) {
+            $this->setRequestOptions(
+                $endpointProvider,
+                $command,
+                $operation,
+                $commandArgs,
+                $clientArgs,
+                $headers
+            );
+            $this->endpoint = new Uri($this->endpoint);
         }
-
         $uri = $this->buildEndpoint($operation, $commandArgs, $opts);
 
         return new Request(
             $operation['http']['method'],
             $uri,
             $headers,
-            $opts['body'] ?? null
+            isset($opts['body']) ? $opts['body'] : null
         );
     }
 
diff --git a/src/AwsClient.php b/src/AwsClient.php
index 7cd70a5e2a..f372e538e1 100644
--- a/src/AwsClient.php
+++ b/src/AwsClient.php
@@ -6,7 +6,6 @@
 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;
@@ -241,9 +240,7 @@ public function __construct(array $args)
         $this->loadAliases();
         $this->addStreamRequestPayload();
         $this->addRecursionDetection();
-        if ($this->isUseEndpointV2()) {
-            $this->addEndpointV2Middleware();
-        }
+        $this->addRequestBuilder();
 
         if (!is_null($this->api->getMetadata('awsQueryCompatible'))) {
             $this->addQueryCompatibleInputMiddleware($this->api);
@@ -515,18 +512,24 @@ private function addRecursionDetection()
         );
     }
 
-    private function addEndpointV2Middleware()
+    /**
+     * Adds the `builder` middleware such that a client's endpoint
+     * provider and endpoint resolution arguments can be passed.
+     */
+    private function addRequestBuilder()
     {
-        $list = $this->getHandlerList();
+        $handlerList = $this->getHandlerList();
+        $serializer = $this->serializer;
+        $endpointProvider = $this->endpointProvider;
         $endpointArgs = $this->getEndpointProviderArgs();
 
-        $list->prependBuild(
-            EndpointV2Middleware::wrap(
-                $this->endpointProvider,
-                $this->getApi(),
+        $handlerList->prependBuild(
+            Middleware::requestBuilder(
+                $serializer,
+                $endpointProvider,
                 $endpointArgs
             ),
-            'endpointV2_middleware'
+            'builderV2'
         );
     }
 
diff --git a/src/ClientResolver.php b/src/ClientResolver.php
index 2414f0aea2..69f4439d91 100644
--- a/src/ClientResolver.php
+++ b/src/ClientResolver.php
@@ -153,7 +153,6 @@ class ClientResolver
         ],
         'serializer' => [
             'default'   => [__CLASS__, '_default_serializer'],
-            'fn'        => [__CLASS__, '_apply_serializer'],
             'internal'  => true,
             'type'      => 'value',
             'valid'     => ['callable'],
@@ -835,11 +834,6 @@ 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
deleted file mode 100644
index beddfdc656..0000000000
--- a/src/EndpointV2/EndpointV2Middleware.php
+++ /dev/null
@@ -1,292 +0,0 @@
-<?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 3bcef17ac8..922ec189ec 100644
--- a/src/EndpointV2/EndpointV2SerializerTrait.php
+++ b/src/EndpointV2/EndpointV2SerializerTrait.php
@@ -3,7 +3,6 @@
 namespace Aws\EndpointV2;
 
 use Aws\Api\Serializer\RestSerializer;
-use Aws\EndpointV2\Ruleset\RulesetEndpoint;
 use GuzzleHttp\Psr7\Uri;
 
 /**
@@ -15,35 +14,144 @@
 trait EndpointV2SerializerTrait
 {
     /**
-     * Applies a resolved endpoint, headers and any custom HTTP schemes provided
-     * in client configuration to options which are applied to the serialized request.
+     * 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.
      *
-     * @param $endpoint
-     * @param $headers
-     *
-     * @return void
+     * @internal
      */
-    private function setEndpointV2RequestOptions(
-        RulesetEndpoint $endpoint,
-        array &$headers
-    ): void
+    private function setRequestOptions(
+        $endpointProvider,
+        $command,
+        $operation,
+        $commandArgs,
+        $clientArgs,
+        &$headers
+    )
     {
-        $this->applyHeaders($endpoint, $headers);
+        $providerArgs = $this->resolveProviderArgs(
+            $endpointProvider,
+            $operation,
+            $commandArgs,
+            $clientArgs
+        );
+        $endpoint = $endpointProvider->resolveEndpoint($providerArgs);
         $resolvedUrl = $endpoint->getUrl();
+
         $this->applyScheme($resolvedUrl);
-        $this->endpoint = $this instanceof RestSerializer
-            ? new Uri($resolvedUrl)
-            : $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;
     }
 
     /**
-     * Combines modeled headers and headers resolved from an endpoint object.
-     *
-     * @param $endpoint
-     * @param $headers
-     * @return void
+     * 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.
      */
-    private function applyHeaders(RulesetEndpoint $endpoint, array &$headers): 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, &$headers)
     {
         if (!is_null($endpoint->getHeaders())) {
            $headers = array_merge(
@@ -53,13 +161,71 @@ private function applyHeaders(RulesetEndpoint $endpoint, array &$headers): void
         }
     }
 
-    /**
-     * Applies custom HTTP schemes provided in client configuration.
-     *
-     * @param $resolvedUrl
-     * @return void
-     */
-    private function applyScheme(string &$resolvedUrl): void
+    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)
     {
         $resolvedEndpointScheme = parse_url($resolvedUrl, PHP_URL_SCHEME);
         $scheme = $this->endpoint instanceof Uri
diff --git a/src/EndpointV2/Rule/AbstractRule.php b/src/EndpointV2/Rule/AbstractRule.php
index adedb4e199..94da12d01b 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 c3a0e9b7e5..b6b276d70c 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 21828c1951..aa4d26e07f 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 bc5504458a..59f4bf18a2 100644
--- a/src/Middleware.php
+++ b/src/Middleware.php
@@ -100,11 +100,15 @@ public static function validation(Service $api, Validator $validator = null)
      * @param array $providerArgs
      * @return callable
      */
-    public static function requestBuilder($serializer)
+    public static function requestBuilder(
+        $serializer,
+        $endpointProvider = null,
+        array $providerArgs = null
+    )
     {
-        return function (callable $handler) use ($serializer) {
-            return function (CommandInterface $command, $endpoint = null) use ($serializer, $handler) {
-                return $handler($command, $serializer($command, $endpoint));
+        return function (callable $handler) use ($serializer, $endpointProvider, $providerArgs) {
+            return function (CommandInterface $command) use ($serializer, $handler, $endpointProvider, $providerArgs) {
+                return $handler($command, $serializer($command, $endpointProvider, $providerArgs));
             };
         };
     }
diff --git a/src/S3/S3Client.php b/src/S3/S3Client.php
index 12d6201fe3..b82bbc56bc 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('builder',
+            $stack->after('builderV2',
                 's3.check_empty_path_with_query',
                 $this->getEmptyPathWithQuery());
         }
diff --git a/src/S3/StreamWrapper.php b/src/S3/StreamWrapper.php
index 955b39dfa7..a70e5cd52d 100644
--- a/src/S3/StreamWrapper.php
+++ b/src/S3/StreamWrapper.php
@@ -245,7 +245,6 @@ 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 23c6f111aa..81db7560b5 100644
--- a/tests/Api/Serializer/JsonRpcSerializerTest.php
+++ b/tests/Api/Serializer/JsonRpcSerializerTest.php
@@ -6,7 +6,6 @@
 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;
 
@@ -83,8 +82,14 @@ function () {}
 
         $q = new JsonRpcSerializer($service, 'http://foo.com');
         $cmd = new Command('foo', ['baz' => []]);
-        $endpoint = new RulesetEndpoint('https://foo.com');
-        $request = $q($cmd, $endpoint);
-        $this->assertSame('http://foo.com', (string) $request->getUri());
+        $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());
     }
 }
diff --git a/tests/Api/Serializer/QuerySerializerTest.php b/tests/Api/Serializer/QuerySerializerTest.php
index 3edecc1edc..263aa43e93 100644
--- a/tests/Api/Serializer/QuerySerializerTest.php
+++ b/tests/Api/Serializer/QuerySerializerTest.php
@@ -6,7 +6,6 @@
 use Aws\Command;
 use Aws\EndpointV2\EndpointDefinitionProvider;
 use Aws\EndpointV2\EndpointProviderV2;
-use Aws\EndpointV2\Ruleset\RulesetEndpoint;
 use Aws\Test\UsesServiceTrait;
 use PHPUnit\Framework\TestCase;
 
@@ -80,8 +79,14 @@ function () {}
 
         $q = new QuerySerializer($service, 'http://foo.com');
         $cmd = new Command('foo', ['baz' => []]);
-        $endpoint = new RulesetEndpoint('https://foo.com');
-        $request = $q($cmd, $endpoint);
-        $this->assertSame('http://foo.com', (string) $request->getUri());
+        $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());
     }
 }
diff --git a/tests/Api/Serializer/RestJsonSerializerTest.php b/tests/Api/Serializer/RestJsonSerializerTest.php
index 3f6ea6c33f..316ea20115 100644
--- a/tests/Api/Serializer/RestJsonSerializerTest.php
+++ b/tests/Api/Serializer/RestJsonSerializerTest.php
@@ -6,7 +6,6 @@
 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;
 
@@ -348,9 +347,15 @@ public function testDoesNotOverrideScheme()
     {
         $serializer = new RestJsonSerializer($this->getTestService(), 'http://foo.com');
         $cmd = new Command('foo', ['baz' => 'bar']);
-        $endpoint = new RulesetEndpoint('https://foo.com');
-        $request = $serializer($cmd, $endpoint);
-        $this->assertSame('http://foo.com/', (string) $request->getUri());
+        $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());
     }
 }
 
diff --git a/tests/Api/Serializer/RestXmlSerializerTest.php b/tests/Api/Serializer/RestXmlSerializerTest.php
index 6908b5762a..7ed0bf4ed3 100644
--- a/tests/Api/Serializer/RestXmlSerializerTest.php
+++ b/tests/Api/Serializer/RestXmlSerializerTest.php
@@ -6,7 +6,6 @@
 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;
 
@@ -112,8 +111,14 @@ public function testDoesNotOverrideScheme()
         $client = $this->getTestClient('s3', ['region' => 'us-east-1']);
         $serializer = new RestXmlSerializer($client->getApi(), 'http://test.com');
         $cmd = new Command('HeadObject', ['baz' => []]);
-        $endpoint = new RulesetEndpoint('https://foo.com');
-        $request = $serializer($cmd, $endpoint);
-        $this->assertSame('http://foo.com/', (string) $request->getUri());
+        $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());
     }
 }
diff --git a/tests/EndpointV2/EndpointV2MiddlewareTest.php b/tests/EndpointV2/EndpointV2MiddlewareTest.php
deleted file mode 100644
index bc36b9bed1..0000000000
--- a/tests/EndpointV2/EndpointV2MiddlewareTest.php
+++ /dev/null
@@ -1,206 +0,0 @@
-<?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');
-    }
-}