diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/PhpNextgenClientCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/PhpNextgenClientCodegen.java
index 6f79932b56fe..8c3efe9baa49 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/PhpNextgenClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/PhpNextgenClientCodegen.java
@@ -203,7 +203,11 @@ public OperationsMap postProcessOperationsWithModels(OperationsMap objs, List<Mo
                 if (param.isArray || param.isMap) {
                     param.vendorExtensions.putIfAbsent("x-php-param-type", "array");
                 } else {
-                    param.vendorExtensions.putIfAbsent("x-php-param-type", param.dataType);
+                    String paramType = param.dataType;
+                    if ((!param.required || param.isNullable) && !paramType.equals("mixed")) { // optional or nullable but not mixed
+                        paramType = "?" + paramType;
+                    }
+                    param.vendorExtensions.putIfAbsent("x-php-param-type", paramType);
                 }
             }
         }
diff --git a/modules/openapi-generator/src/main/resources/php-nextgen/api.mustache b/modules/openapi-generator/src/main/resources/php-nextgen/api.mustache
index 6110545eda62..382f7e01f7b7 100644
--- a/modules/openapi-generator/src/main/resources/php-nextgen/api.mustache
+++ b/modules/openapi-generator/src/main/resources/php-nextgen/api.mustache
@@ -172,7 +172,7 @@ use {{invokerPackage}}\ObjectSerializer;
     public function {{operationId}}(
     {{^vendorExtensions.x-group-parameters}}
     {{#allParams}}
-        {{^required}}?{{/required}}{{vendorExtensions.x-php-param-type}} ${{paramName}}{{^required}} = {{#defaultValue}}{{{.}}}{{/defaultValue}}{{^defaultValue}}null{{/defaultValue}}{{/required}},
+        {{vendorExtensions.x-php-param-type}} ${{paramName}}{{^required}} = {{#defaultValue}}{{{.}}}{{/defaultValue}}{{^defaultValue}}null{{/defaultValue}}{{/required}},
     {{/allParams}}
     {{#servers}}
     {{#-first}}
@@ -247,7 +247,7 @@ use {{invokerPackage}}\ObjectSerializer;
     public function {{operationId}}WithHttpInfo(
     {{^vendorExtensions.x-group-parameters}}
     {{#allParams}}
-        {{^required}}?{{/required}}{{vendorExtensions.x-php-param-type}} ${{paramName}}{{^required}} = {{#defaultValue}}{{{.}}}{{/defaultValue}}{{^defaultValue}}null{{/defaultValue}}{{/required}},
+        {{vendorExtensions.x-php-param-type}} ${{paramName}}{{^required}} = {{#defaultValue}}{{{.}}}{{/defaultValue}}{{^defaultValue}}null{{/defaultValue}}{{/required}},
     {{/allParams}}
     {{#servers}}
     {{#-first}}
@@ -446,7 +446,7 @@ use {{invokerPackage}}\ObjectSerializer;
     public function {{operationId}}Async(
     {{^vendorExtensions.x-group-parameters}}
     {{#allParams}}
-        {{^required}}?{{/required}}{{vendorExtensions.x-php-param-type}} ${{paramName}}{{^required}} = {{#defaultValue}}{{{.}}}{{/defaultValue}}{{^defaultValue}}null{{/defaultValue}}{{/required}},
+        {{vendorExtensions.x-php-param-type}} ${{paramName}}{{^required}} = {{#defaultValue}}{{{.}}}{{/defaultValue}}{{^defaultValue}}null{{/defaultValue}}{{/required}},
     {{/allParams}}
     {{#servers}}
     {{#-first}}
@@ -524,7 +524,7 @@ use {{invokerPackage}}\ObjectSerializer;
     public function {{operationId}}AsyncWithHttpInfo(
     {{^vendorExtensions.x-group-parameters}}
     {{#allParams}}
-        ${{paramName}}{{^required}} = {{#defaultValue}}{{{.}}}{{/defaultValue}}{{^defaultValue}}null{{/defaultValue}}{{/required}},
+        {{vendorExtensions.x-php-param-type}} ${{paramName}}{{^required}} = {{#defaultValue}}{{{.}}}{{/defaultValue}}{{^defaultValue}}null{{/defaultValue}}{{/required}},
     {{/allParams}}
     {{#servers}}
     {{#-first}}
@@ -630,7 +630,7 @@ use {{invokerPackage}}\ObjectSerializer;
     public function {{operationId}}Request(
     {{^vendorExtensions.x-group-parameters}}
     {{#allParams}}
-        ${{paramName}}{{^required}} = {{#defaultValue}}{{{.}}}{{/defaultValue}}{{^defaultValue}}null{{/defaultValue}}{{/required}},
+        {{vendorExtensions.x-php-param-type}} ${{paramName}}{{^required}} = {{#defaultValue}}{{{.}}}{{/defaultValue}}{{^defaultValue}}null{{/defaultValue}}{{/required}},
     {{/allParams}}
     {{#servers}}
     {{#-first}}
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Api/BodyApi.php b/samples/client/echo_api/php-nextgen-streaming/src/Api/BodyApi.php
index abbbbcf1bc00..32de9920511c 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Api/BodyApi.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Api/BodyApi.php
@@ -633,7 +633,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testBodyApplicationOctetstreamBinaryAsyncWithHttpInfo(
-        $body = null,
+        ?\Psr\Http\Message\StreamInterface $body = null,
         string $contentType = self::contentTypes['testBodyApplicationOctetstreamBinary'][0]
     ): PromiseInterface
     {
@@ -686,7 +686,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testBodyApplicationOctetstreamBinaryRequest(
-        $body = null,
+        ?\Psr\Http\Message\StreamInterface $body = null,
         string $contentType = self::contentTypes['testBodyApplicationOctetstreamBinary'][0]
     ): Request
     {
@@ -949,7 +949,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testBodyMultipartFormdataArrayOfBinaryAsyncWithHttpInfo(
-        $files,
+        array $files,
         string $contentType = self::contentTypes['testBodyMultipartFormdataArrayOfBinary'][0]
     ): PromiseInterface
     {
@@ -1002,7 +1002,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testBodyMultipartFormdataArrayOfBinaryRequest(
-        $files,
+        array $files,
         string $contentType = self::contentTypes['testBodyMultipartFormdataArrayOfBinary'][0]
     ): Request
     {
@@ -1278,7 +1278,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testBodyMultipartFormdataSingleBinaryAsyncWithHttpInfo(
-        $my_file = null,
+        ?\Psr\Http\Message\StreamInterface $my_file = null,
         string $contentType = self::contentTypes['testBodyMultipartFormdataSingleBinary'][0]
     ): PromiseInterface
     {
@@ -1331,7 +1331,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testBodyMultipartFormdataSingleBinaryRequest(
-        $my_file = null,
+        ?\Psr\Http\Message\StreamInterface $my_file = null,
         string $contentType = self::contentTypes['testBodyMultipartFormdataSingleBinary'][0]
     ): Request
     {
@@ -1601,7 +1601,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testEchoBodyAllOfPetAsyncWithHttpInfo(
-        $pet = null,
+        ?\OpenAPI\Client\Model\Pet $pet = null,
         string $contentType = self::contentTypes['testEchoBodyAllOfPet'][0]
     ): PromiseInterface
     {
@@ -1654,7 +1654,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testEchoBodyAllOfPetRequest(
-        $pet = null,
+        ?\OpenAPI\Client\Model\Pet $pet = null,
         string $contentType = self::contentTypes['testEchoBodyAllOfPet'][0]
     ): Request
     {
@@ -1745,7 +1745,7 @@ public function testEchoBodyAllOfPetRequest(
      * @return string
      */
     public function testEchoBodyFreeFormObjectResponseString(
-        ?array $body = null,
+        array $body = null,
         string $contentType = self::contentTypes['testEchoBodyFreeFormObjectResponseString'][0]
     ): string
     {
@@ -1766,7 +1766,7 @@ public function testEchoBodyFreeFormObjectResponseString(
      * @return array of string, HTTP status code, HTTP response headers (array of strings)
      */
     public function testEchoBodyFreeFormObjectResponseStringWithHttpInfo(
-        ?array $body = null,
+        array $body = null,
         string $contentType = self::contentTypes['testEchoBodyFreeFormObjectResponseString'][0]
     ): array
     {
@@ -1893,7 +1893,7 @@ public function testEchoBodyFreeFormObjectResponseStringWithHttpInfo(
      * @return PromiseInterface
      */
     public function testEchoBodyFreeFormObjectResponseStringAsync(
-        ?array $body = null,
+        array $body = null,
         string $contentType = self::contentTypes['testEchoBodyFreeFormObjectResponseString'][0]
     ): PromiseInterface
     {
@@ -1917,7 +1917,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testEchoBodyFreeFormObjectResponseStringAsyncWithHttpInfo(
-        $body = null,
+        array $body = null,
         string $contentType = self::contentTypes['testEchoBodyFreeFormObjectResponseString'][0]
     ): PromiseInterface
     {
@@ -1970,7 +1970,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testEchoBodyFreeFormObjectResponseStringRequest(
-        $body = null,
+        array $body = null,
         string $contentType = self::contentTypes['testEchoBodyFreeFormObjectResponseString'][0]
     ): Request
     {
@@ -2233,7 +2233,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testEchoBodyPetAsyncWithHttpInfo(
-        $pet = null,
+        ?\OpenAPI\Client\Model\Pet $pet = null,
         string $contentType = self::contentTypes['testEchoBodyPet'][0]
     ): PromiseInterface
     {
@@ -2286,7 +2286,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testEchoBodyPetRequest(
-        $pet = null,
+        ?\OpenAPI\Client\Model\Pet $pet = null,
         string $contentType = self::contentTypes['testEchoBodyPet'][0]
     ): Request
     {
@@ -2549,7 +2549,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testEchoBodyPetResponseStringAsyncWithHttpInfo(
-        $pet = null,
+        ?\OpenAPI\Client\Model\Pet $pet = null,
         string $contentType = self::contentTypes['testEchoBodyPetResponseString'][0]
     ): PromiseInterface
     {
@@ -2602,7 +2602,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testEchoBodyPetResponseStringRequest(
-        $pet = null,
+        ?\OpenAPI\Client\Model\Pet $pet = null,
         string $contentType = self::contentTypes['testEchoBodyPetResponseString'][0]
     ): Request
     {
@@ -2865,7 +2865,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testEchoBodyStringEnumAsyncWithHttpInfo(
-        $body = null,
+        ?string $body = null,
         string $contentType = self::contentTypes['testEchoBodyStringEnum'][0]
     ): PromiseInterface
     {
@@ -2918,7 +2918,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testEchoBodyStringEnumRequest(
-        $body = null,
+        ?string $body = null,
         string $contentType = self::contentTypes['testEchoBodyStringEnum'][0]
     ): Request
     {
@@ -3181,7 +3181,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testEchoBodyTagResponseStringAsyncWithHttpInfo(
-        $tag = null,
+        ?\OpenAPI\Client\Model\Tag $tag = null,
         string $contentType = self::contentTypes['testEchoBodyTagResponseString'][0]
     ): PromiseInterface
     {
@@ -3234,7 +3234,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testEchoBodyTagResponseStringRequest(
-        $tag = null,
+        ?\OpenAPI\Client\Model\Tag $tag = null,
         string $contentType = self::contentTypes['testEchoBodyTagResponseString'][0]
     ): Request
     {
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Api/FormApi.php b/samples/client/echo_api/php-nextgen-streaming/src/Api/FormApi.php
index 241754b30b08..ddaa5c47ab6c 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Api/FormApi.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Api/FormApi.php
@@ -328,9 +328,9 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testFormIntegerBooleanStringAsyncWithHttpInfo(
-        $integer_form = null,
-        $boolean_form = null,
-        $string_form = null,
+        ?int $integer_form = null,
+        ?bool $boolean_form = null,
+        ?string $string_form = null,
         string $contentType = self::contentTypes['testFormIntegerBooleanString'][0]
     ): PromiseInterface
     {
@@ -385,9 +385,9 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testFormIntegerBooleanStringRequest(
-        $integer_form = null,
-        $boolean_form = null,
-        $string_form = null,
+        ?int $integer_form = null,
+        ?bool $boolean_form = null,
+        ?string $string_form = null,
         string $contentType = self::contentTypes['testFormIntegerBooleanString'][0]
     ): Request
     {
@@ -657,7 +657,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testFormObjectMultipartAsyncWithHttpInfo(
-        $marker,
+        \OpenAPI\Client\Model\TestFormObjectMultipartRequestMarker $marker,
         string $contentType = self::contentTypes['testFormObjectMultipart'][0]
     ): PromiseInterface
     {
@@ -710,7 +710,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testFormObjectMultipartRequest(
-        $marker,
+        \OpenAPI\Client\Model\TestFormObjectMultipartRequestMarker $marker,
         string $contentType = self::contentTypes['testFormObjectMultipart'][0]
     ): Request
     {
@@ -1011,12 +1011,12 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testFormOneofAsyncWithHttpInfo(
-        $form1 = null,
-        $form2 = null,
-        $form3 = null,
-        $form4 = null,
-        $id = null,
-        $name = null,
+        ?string $form1 = null,
+        ?int $form2 = null,
+        ?string $form3 = null,
+        ?bool $form4 = null,
+        ?int $id = null,
+        ?string $name = null,
         string $contentType = self::contentTypes['testFormOneof'][0]
     ): PromiseInterface
     {
@@ -1074,12 +1074,12 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testFormOneofRequest(
-        $form1 = null,
-        $form2 = null,
-        $form3 = null,
-        $form4 = null,
-        $id = null,
-        $name = null,
+        ?string $form1 = null,
+        ?int $form2 = null,
+        ?string $form3 = null,
+        ?bool $form4 = null,
+        ?int $id = null,
+        ?string $name = null,
         string $contentType = self::contentTypes['testFormOneof'][0]
     ): Request
     {
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Api/HeaderApi.php b/samples/client/echo_api/php-nextgen-streaming/src/Api/HeaderApi.php
index 871fd002020b..3337854a883e 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Api/HeaderApi.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Api/HeaderApi.php
@@ -336,11 +336,11 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testHeaderIntegerBooleanStringEnumsAsyncWithHttpInfo(
-        $integer_header = null,
-        $boolean_header = null,
-        $string_header = null,
-        $enum_nonref_string_header = null,
-        $enum_ref_string_header = null,
+        ?int $integer_header = null,
+        ?bool $boolean_header = null,
+        ?string $string_header = null,
+        ?string $enum_nonref_string_header = null,
+        ?\OpenAPI\Client\Model\StringEnumRef $enum_ref_string_header = null,
         string $contentType = self::contentTypes['testHeaderIntegerBooleanStringEnums'][0]
     ): PromiseInterface
     {
@@ -397,11 +397,11 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testHeaderIntegerBooleanStringEnumsRequest(
-        $integer_header = null,
-        $boolean_header = null,
-        $string_header = null,
-        $enum_nonref_string_header = null,
-        $enum_ref_string_header = null,
+        ?int $integer_header = null,
+        ?bool $boolean_header = null,
+        ?string $string_header = null,
+        ?string $enum_nonref_string_header = null,
+        ?\OpenAPI\Client\Model\StringEnumRef $enum_ref_string_header = null,
         string $contentType = self::contentTypes['testHeaderIntegerBooleanStringEnums'][0]
     ): Request
     {
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Api/PathApi.php b/samples/client/echo_api/php-nextgen-streaming/src/Api/PathApi.php
index e806d61c9453..c6a13a2a6f14 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Api/PathApi.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Api/PathApi.php
@@ -329,10 +329,10 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testsPathStringPathStringIntegerPathIntegerEnumNonrefStringPathEnumRefStringPathAsyncWithHttpInfo(
-        $path_string,
-        $path_integer,
-        $enum_nonref_string_path,
-        $enum_ref_string_path,
+        string $path_string,
+        int $path_integer,
+        string $enum_nonref_string_path,
+        \OpenAPI\Client\Model\StringEnumRef $enum_ref_string_path,
         string $contentType = self::contentTypes['testsPathStringPathStringIntegerPathIntegerEnumNonrefStringPathEnumRefStringPath'][0]
     ): PromiseInterface
     {
@@ -388,10 +388,10 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testsPathStringPathStringIntegerPathIntegerEnumNonrefStringPathEnumRefStringPathRequest(
-        $path_string,
-        $path_integer,
-        $enum_nonref_string_path,
-        $enum_ref_string_path,
+        string $path_string,
+        int $path_integer,
+        string $enum_nonref_string_path,
+        \OpenAPI\Client\Model\StringEnumRef $enum_ref_string_path,
         string $contentType = self::contentTypes['testsPathStringPathStringIntegerPathIntegerEnumNonrefStringPathEnumRefStringPath'][0]
     ): Request
     {
diff --git a/samples/client/echo_api/php-nextgen-streaming/src/Api/QueryApi.php b/samples/client/echo_api/php-nextgen-streaming/src/Api/QueryApi.php
index 8e64ba5648ce..f0e76da188be 100644
--- a/samples/client/echo_api/php-nextgen-streaming/src/Api/QueryApi.php
+++ b/samples/client/echo_api/php-nextgen-streaming/src/Api/QueryApi.php
@@ -342,8 +342,8 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testEnumRefStringAsyncWithHttpInfo(
-        $enum_nonref_string_query = null,
-        $enum_ref_string_query = null,
+        ?string $enum_nonref_string_query = null,
+        ?\OpenAPI\Client\Model\StringEnumRef $enum_ref_string_query = null,
         string $contentType = self::contentTypes['testEnumRefString'][0]
     ): PromiseInterface
     {
@@ -397,8 +397,8 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testEnumRefStringRequest(
-        $enum_nonref_string_query = null,
-        $enum_ref_string_query = null,
+        ?string $enum_nonref_string_query = null,
+        ?\OpenAPI\Client\Model\StringEnumRef $enum_ref_string_query = null,
         string $contentType = self::contentTypes['testEnumRefString'][0]
     ): Request
     {
@@ -687,9 +687,9 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testQueryDatetimeDateStringAsyncWithHttpInfo(
-        $datetime_query = null,
-        $date_query = null,
-        $string_query = null,
+        ?\DateTime $datetime_query = null,
+        ?\DateTime $date_query = null,
+        ?string $string_query = null,
         string $contentType = self::contentTypes['testQueryDatetimeDateString'][0]
     ): PromiseInterface
     {
@@ -744,9 +744,9 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryDatetimeDateStringRequest(
-        $datetime_query = null,
-        $date_query = null,
-        $string_query = null,
+        ?\DateTime $datetime_query = null,
+        ?\DateTime $date_query = null,
+        ?string $string_query = null,
         string $contentType = self::contentTypes['testQueryDatetimeDateString'][0]
     ): Request
     {
@@ -1045,9 +1045,9 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testQueryIntegerBooleanStringAsyncWithHttpInfo(
-        $integer_query = null,
-        $boolean_query = null,
-        $string_query = null,
+        ?int $integer_query = null,
+        ?bool $boolean_query = null,
+        ?string $string_query = null,
         string $contentType = self::contentTypes['testQueryIntegerBooleanString'][0]
     ): PromiseInterface
     {
@@ -1102,9 +1102,9 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryIntegerBooleanStringRequest(
-        $integer_query = null,
-        $boolean_query = null,
-        $string_query = null,
+        ?int $integer_query = null,
+        ?bool $boolean_query = null,
+        ?string $string_query = null,
         string $contentType = self::contentTypes['testQueryIntegerBooleanString'][0]
     ): Request
     {
@@ -1389,7 +1389,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testQueryStyleDeepObjectExplodeTrueObjectAsyncWithHttpInfo(
-        $query_object = null,
+        ?\OpenAPI\Client\Model\Pet $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleDeepObjectExplodeTrueObject'][0]
     ): PromiseInterface
     {
@@ -1442,7 +1442,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryStyleDeepObjectExplodeTrueObjectRequest(
-        $query_object = null,
+        ?\OpenAPI\Client\Model\Pet $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleDeepObjectExplodeTrueObject'][0]
     ): Request
     {
@@ -1707,7 +1707,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testQueryStyleDeepObjectExplodeTrueObjectAllOfAsyncWithHttpInfo(
-        $query_object = null,
+        ?\OpenAPI\Client\Model\TestQueryStyleDeepObjectExplodeTrueObjectAllOfQueryObjectParameter $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleDeepObjectExplodeTrueObjectAllOf'][0]
     ): PromiseInterface
     {
@@ -1760,7 +1760,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryStyleDeepObjectExplodeTrueObjectAllOfRequest(
-        $query_object = null,
+        ?\OpenAPI\Client\Model\TestQueryStyleDeepObjectExplodeTrueObjectAllOfQueryObjectParameter $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleDeepObjectExplodeTrueObjectAllOf'][0]
     ): Request
     {
@@ -1853,7 +1853,7 @@ public function testQueryStyleDeepObjectExplodeTrueObjectAllOfRequest(
      * @return string
      */
     public function testQueryStyleFormExplodeFalseArrayInteger(
-        ?array $query_object = null,
+        array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayInteger'][0]
     ): string
     {
@@ -1874,7 +1874,7 @@ public function testQueryStyleFormExplodeFalseArrayInteger(
      * @return array of string, HTTP status code, HTTP response headers (array of strings)
      */
     public function testQueryStyleFormExplodeFalseArrayIntegerWithHttpInfo(
-        ?array $query_object = null,
+        array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayInteger'][0]
     ): array
     {
@@ -2001,7 +2001,7 @@ public function testQueryStyleFormExplodeFalseArrayIntegerWithHttpInfo(
      * @return PromiseInterface
      */
     public function testQueryStyleFormExplodeFalseArrayIntegerAsync(
-        ?array $query_object = null,
+        array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayInteger'][0]
     ): PromiseInterface
     {
@@ -2025,7 +2025,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testQueryStyleFormExplodeFalseArrayIntegerAsyncWithHttpInfo(
-        $query_object = null,
+        array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayInteger'][0]
     ): PromiseInterface
     {
@@ -2078,7 +2078,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryStyleFormExplodeFalseArrayIntegerRequest(
-        $query_object = null,
+        array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayInteger'][0]
     ): Request
     {
@@ -2171,7 +2171,7 @@ public function testQueryStyleFormExplodeFalseArrayIntegerRequest(
      * @return string
      */
     public function testQueryStyleFormExplodeFalseArrayString(
-        ?array $query_object = null,
+        array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayString'][0]
     ): string
     {
@@ -2192,7 +2192,7 @@ public function testQueryStyleFormExplodeFalseArrayString(
      * @return array of string, HTTP status code, HTTP response headers (array of strings)
      */
     public function testQueryStyleFormExplodeFalseArrayStringWithHttpInfo(
-        ?array $query_object = null,
+        array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayString'][0]
     ): array
     {
@@ -2319,7 +2319,7 @@ public function testQueryStyleFormExplodeFalseArrayStringWithHttpInfo(
      * @return PromiseInterface
      */
     public function testQueryStyleFormExplodeFalseArrayStringAsync(
-        ?array $query_object = null,
+        array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayString'][0]
     ): PromiseInterface
     {
@@ -2343,7 +2343,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testQueryStyleFormExplodeFalseArrayStringAsyncWithHttpInfo(
-        $query_object = null,
+        array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayString'][0]
     ): PromiseInterface
     {
@@ -2396,7 +2396,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryStyleFormExplodeFalseArrayStringRequest(
-        $query_object = null,
+        array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayString'][0]
     ): Request
     {
@@ -2661,7 +2661,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testQueryStyleFormExplodeTrueArrayStringAsyncWithHttpInfo(
-        $query_object = null,
+        ?\OpenAPI\Client\Model\TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeTrueArrayString'][0]
     ): PromiseInterface
     {
@@ -2714,7 +2714,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryStyleFormExplodeTrueArrayStringRequest(
-        $query_object = null,
+        ?\OpenAPI\Client\Model\TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeTrueArrayString'][0]
     ): Request
     {
@@ -2979,7 +2979,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testQueryStyleFormExplodeTrueObjectAsyncWithHttpInfo(
-        $query_object = null,
+        ?\OpenAPI\Client\Model\Pet $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeTrueObject'][0]
     ): PromiseInterface
     {
@@ -3032,7 +3032,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryStyleFormExplodeTrueObjectRequest(
-        $query_object = null,
+        ?\OpenAPI\Client\Model\Pet $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeTrueObject'][0]
     ): Request
     {
@@ -3297,7 +3297,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testQueryStyleFormExplodeTrueObjectAllOfAsyncWithHttpInfo(
-        $query_object = null,
+        ?\OpenAPI\Client\Model\DataQuery $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeTrueObjectAllOf'][0]
     ): PromiseInterface
     {
@@ -3350,7 +3350,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryStyleFormExplodeTrueObjectAllOfRequest(
-        $query_object = null,
+        ?\OpenAPI\Client\Model\DataQuery $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeTrueObjectAllOf'][0]
     ): Request
     {
diff --git a/samples/client/echo_api/php-nextgen/src/Api/BodyApi.php b/samples/client/echo_api/php-nextgen/src/Api/BodyApi.php
index 1b49ec023e98..fec58cc88f2d 100644
--- a/samples/client/echo_api/php-nextgen/src/Api/BodyApi.php
+++ b/samples/client/echo_api/php-nextgen/src/Api/BodyApi.php
@@ -633,7 +633,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testBodyApplicationOctetstreamBinaryAsyncWithHttpInfo(
-        $body = null,
+        ?\SplFileObject $body = null,
         string $contentType = self::contentTypes['testBodyApplicationOctetstreamBinary'][0]
     ): PromiseInterface
     {
@@ -686,7 +686,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testBodyApplicationOctetstreamBinaryRequest(
-        $body = null,
+        ?\SplFileObject $body = null,
         string $contentType = self::contentTypes['testBodyApplicationOctetstreamBinary'][0]
     ): Request
     {
@@ -949,7 +949,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testBodyMultipartFormdataArrayOfBinaryAsyncWithHttpInfo(
-        $files,
+        array $files,
         string $contentType = self::contentTypes['testBodyMultipartFormdataArrayOfBinary'][0]
     ): PromiseInterface
     {
@@ -1002,7 +1002,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testBodyMultipartFormdataArrayOfBinaryRequest(
-        $files,
+        array $files,
         string $contentType = self::contentTypes['testBodyMultipartFormdataArrayOfBinary'][0]
     ): Request
     {
@@ -1278,7 +1278,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testBodyMultipartFormdataSingleBinaryAsyncWithHttpInfo(
-        $my_file = null,
+        ?\SplFileObject $my_file = null,
         string $contentType = self::contentTypes['testBodyMultipartFormdataSingleBinary'][0]
     ): PromiseInterface
     {
@@ -1331,7 +1331,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testBodyMultipartFormdataSingleBinaryRequest(
-        $my_file = null,
+        ?\SplFileObject $my_file = null,
         string $contentType = self::contentTypes['testBodyMultipartFormdataSingleBinary'][0]
     ): Request
     {
@@ -1601,7 +1601,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testEchoBodyAllOfPetAsyncWithHttpInfo(
-        $pet = null,
+        ?\OpenAPI\Client\Model\Pet $pet = null,
         string $contentType = self::contentTypes['testEchoBodyAllOfPet'][0]
     ): PromiseInterface
     {
@@ -1654,7 +1654,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testEchoBodyAllOfPetRequest(
-        $pet = null,
+        ?\OpenAPI\Client\Model\Pet $pet = null,
         string $contentType = self::contentTypes['testEchoBodyAllOfPet'][0]
     ): Request
     {
@@ -1745,7 +1745,7 @@ public function testEchoBodyAllOfPetRequest(
      * @return string
      */
     public function testEchoBodyFreeFormObjectResponseString(
-        ?array $body = null,
+        array $body = null,
         string $contentType = self::contentTypes['testEchoBodyFreeFormObjectResponseString'][0]
     ): string
     {
@@ -1766,7 +1766,7 @@ public function testEchoBodyFreeFormObjectResponseString(
      * @return array of string, HTTP status code, HTTP response headers (array of strings)
      */
     public function testEchoBodyFreeFormObjectResponseStringWithHttpInfo(
-        ?array $body = null,
+        array $body = null,
         string $contentType = self::contentTypes['testEchoBodyFreeFormObjectResponseString'][0]
     ): array
     {
@@ -1893,7 +1893,7 @@ public function testEchoBodyFreeFormObjectResponseStringWithHttpInfo(
      * @return PromiseInterface
      */
     public function testEchoBodyFreeFormObjectResponseStringAsync(
-        ?array $body = null,
+        array $body = null,
         string $contentType = self::contentTypes['testEchoBodyFreeFormObjectResponseString'][0]
     ): PromiseInterface
     {
@@ -1917,7 +1917,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testEchoBodyFreeFormObjectResponseStringAsyncWithHttpInfo(
-        $body = null,
+        array $body = null,
         string $contentType = self::contentTypes['testEchoBodyFreeFormObjectResponseString'][0]
     ): PromiseInterface
     {
@@ -1970,7 +1970,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testEchoBodyFreeFormObjectResponseStringRequest(
-        $body = null,
+        array $body = null,
         string $contentType = self::contentTypes['testEchoBodyFreeFormObjectResponseString'][0]
     ): Request
     {
@@ -2233,7 +2233,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testEchoBodyPetAsyncWithHttpInfo(
-        $pet = null,
+        ?\OpenAPI\Client\Model\Pet $pet = null,
         string $contentType = self::contentTypes['testEchoBodyPet'][0]
     ): PromiseInterface
     {
@@ -2286,7 +2286,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testEchoBodyPetRequest(
-        $pet = null,
+        ?\OpenAPI\Client\Model\Pet $pet = null,
         string $contentType = self::contentTypes['testEchoBodyPet'][0]
     ): Request
     {
@@ -2549,7 +2549,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testEchoBodyPetResponseStringAsyncWithHttpInfo(
-        $pet = null,
+        ?\OpenAPI\Client\Model\Pet $pet = null,
         string $contentType = self::contentTypes['testEchoBodyPetResponseString'][0]
     ): PromiseInterface
     {
@@ -2602,7 +2602,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testEchoBodyPetResponseStringRequest(
-        $pet = null,
+        ?\OpenAPI\Client\Model\Pet $pet = null,
         string $contentType = self::contentTypes['testEchoBodyPetResponseString'][0]
     ): Request
     {
@@ -2865,7 +2865,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testEchoBodyStringEnumAsyncWithHttpInfo(
-        $body = null,
+        ?string $body = null,
         string $contentType = self::contentTypes['testEchoBodyStringEnum'][0]
     ): PromiseInterface
     {
@@ -2918,7 +2918,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testEchoBodyStringEnumRequest(
-        $body = null,
+        ?string $body = null,
         string $contentType = self::contentTypes['testEchoBodyStringEnum'][0]
     ): Request
     {
@@ -3181,7 +3181,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testEchoBodyTagResponseStringAsyncWithHttpInfo(
-        $tag = null,
+        ?\OpenAPI\Client\Model\Tag $tag = null,
         string $contentType = self::contentTypes['testEchoBodyTagResponseString'][0]
     ): PromiseInterface
     {
@@ -3234,7 +3234,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testEchoBodyTagResponseStringRequest(
-        $tag = null,
+        ?\OpenAPI\Client\Model\Tag $tag = null,
         string $contentType = self::contentTypes['testEchoBodyTagResponseString'][0]
     ): Request
     {
diff --git a/samples/client/echo_api/php-nextgen/src/Api/FormApi.php b/samples/client/echo_api/php-nextgen/src/Api/FormApi.php
index 241754b30b08..ddaa5c47ab6c 100644
--- a/samples/client/echo_api/php-nextgen/src/Api/FormApi.php
+++ b/samples/client/echo_api/php-nextgen/src/Api/FormApi.php
@@ -328,9 +328,9 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testFormIntegerBooleanStringAsyncWithHttpInfo(
-        $integer_form = null,
-        $boolean_form = null,
-        $string_form = null,
+        ?int $integer_form = null,
+        ?bool $boolean_form = null,
+        ?string $string_form = null,
         string $contentType = self::contentTypes['testFormIntegerBooleanString'][0]
     ): PromiseInterface
     {
@@ -385,9 +385,9 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testFormIntegerBooleanStringRequest(
-        $integer_form = null,
-        $boolean_form = null,
-        $string_form = null,
+        ?int $integer_form = null,
+        ?bool $boolean_form = null,
+        ?string $string_form = null,
         string $contentType = self::contentTypes['testFormIntegerBooleanString'][0]
     ): Request
     {
@@ -657,7 +657,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testFormObjectMultipartAsyncWithHttpInfo(
-        $marker,
+        \OpenAPI\Client\Model\TestFormObjectMultipartRequestMarker $marker,
         string $contentType = self::contentTypes['testFormObjectMultipart'][0]
     ): PromiseInterface
     {
@@ -710,7 +710,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testFormObjectMultipartRequest(
-        $marker,
+        \OpenAPI\Client\Model\TestFormObjectMultipartRequestMarker $marker,
         string $contentType = self::contentTypes['testFormObjectMultipart'][0]
     ): Request
     {
@@ -1011,12 +1011,12 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testFormOneofAsyncWithHttpInfo(
-        $form1 = null,
-        $form2 = null,
-        $form3 = null,
-        $form4 = null,
-        $id = null,
-        $name = null,
+        ?string $form1 = null,
+        ?int $form2 = null,
+        ?string $form3 = null,
+        ?bool $form4 = null,
+        ?int $id = null,
+        ?string $name = null,
         string $contentType = self::contentTypes['testFormOneof'][0]
     ): PromiseInterface
     {
@@ -1074,12 +1074,12 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testFormOneofRequest(
-        $form1 = null,
-        $form2 = null,
-        $form3 = null,
-        $form4 = null,
-        $id = null,
-        $name = null,
+        ?string $form1 = null,
+        ?int $form2 = null,
+        ?string $form3 = null,
+        ?bool $form4 = null,
+        ?int $id = null,
+        ?string $name = null,
         string $contentType = self::contentTypes['testFormOneof'][0]
     ): Request
     {
diff --git a/samples/client/echo_api/php-nextgen/src/Api/HeaderApi.php b/samples/client/echo_api/php-nextgen/src/Api/HeaderApi.php
index 871fd002020b..3337854a883e 100644
--- a/samples/client/echo_api/php-nextgen/src/Api/HeaderApi.php
+++ b/samples/client/echo_api/php-nextgen/src/Api/HeaderApi.php
@@ -336,11 +336,11 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testHeaderIntegerBooleanStringEnumsAsyncWithHttpInfo(
-        $integer_header = null,
-        $boolean_header = null,
-        $string_header = null,
-        $enum_nonref_string_header = null,
-        $enum_ref_string_header = null,
+        ?int $integer_header = null,
+        ?bool $boolean_header = null,
+        ?string $string_header = null,
+        ?string $enum_nonref_string_header = null,
+        ?\OpenAPI\Client\Model\StringEnumRef $enum_ref_string_header = null,
         string $contentType = self::contentTypes['testHeaderIntegerBooleanStringEnums'][0]
     ): PromiseInterface
     {
@@ -397,11 +397,11 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testHeaderIntegerBooleanStringEnumsRequest(
-        $integer_header = null,
-        $boolean_header = null,
-        $string_header = null,
-        $enum_nonref_string_header = null,
-        $enum_ref_string_header = null,
+        ?int $integer_header = null,
+        ?bool $boolean_header = null,
+        ?string $string_header = null,
+        ?string $enum_nonref_string_header = null,
+        ?\OpenAPI\Client\Model\StringEnumRef $enum_ref_string_header = null,
         string $contentType = self::contentTypes['testHeaderIntegerBooleanStringEnums'][0]
     ): Request
     {
diff --git a/samples/client/echo_api/php-nextgen/src/Api/PathApi.php b/samples/client/echo_api/php-nextgen/src/Api/PathApi.php
index e806d61c9453..c6a13a2a6f14 100644
--- a/samples/client/echo_api/php-nextgen/src/Api/PathApi.php
+++ b/samples/client/echo_api/php-nextgen/src/Api/PathApi.php
@@ -329,10 +329,10 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testsPathStringPathStringIntegerPathIntegerEnumNonrefStringPathEnumRefStringPathAsyncWithHttpInfo(
-        $path_string,
-        $path_integer,
-        $enum_nonref_string_path,
-        $enum_ref_string_path,
+        string $path_string,
+        int $path_integer,
+        string $enum_nonref_string_path,
+        \OpenAPI\Client\Model\StringEnumRef $enum_ref_string_path,
         string $contentType = self::contentTypes['testsPathStringPathStringIntegerPathIntegerEnumNonrefStringPathEnumRefStringPath'][0]
     ): PromiseInterface
     {
@@ -388,10 +388,10 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testsPathStringPathStringIntegerPathIntegerEnumNonrefStringPathEnumRefStringPathRequest(
-        $path_string,
-        $path_integer,
-        $enum_nonref_string_path,
-        $enum_ref_string_path,
+        string $path_string,
+        int $path_integer,
+        string $enum_nonref_string_path,
+        \OpenAPI\Client\Model\StringEnumRef $enum_ref_string_path,
         string $contentType = self::contentTypes['testsPathStringPathStringIntegerPathIntegerEnumNonrefStringPathEnumRefStringPath'][0]
     ): Request
     {
diff --git a/samples/client/echo_api/php-nextgen/src/Api/QueryApi.php b/samples/client/echo_api/php-nextgen/src/Api/QueryApi.php
index 8e64ba5648ce..f0e76da188be 100644
--- a/samples/client/echo_api/php-nextgen/src/Api/QueryApi.php
+++ b/samples/client/echo_api/php-nextgen/src/Api/QueryApi.php
@@ -342,8 +342,8 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testEnumRefStringAsyncWithHttpInfo(
-        $enum_nonref_string_query = null,
-        $enum_ref_string_query = null,
+        ?string $enum_nonref_string_query = null,
+        ?\OpenAPI\Client\Model\StringEnumRef $enum_ref_string_query = null,
         string $contentType = self::contentTypes['testEnumRefString'][0]
     ): PromiseInterface
     {
@@ -397,8 +397,8 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testEnumRefStringRequest(
-        $enum_nonref_string_query = null,
-        $enum_ref_string_query = null,
+        ?string $enum_nonref_string_query = null,
+        ?\OpenAPI\Client\Model\StringEnumRef $enum_ref_string_query = null,
         string $contentType = self::contentTypes['testEnumRefString'][0]
     ): Request
     {
@@ -687,9 +687,9 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testQueryDatetimeDateStringAsyncWithHttpInfo(
-        $datetime_query = null,
-        $date_query = null,
-        $string_query = null,
+        ?\DateTime $datetime_query = null,
+        ?\DateTime $date_query = null,
+        ?string $string_query = null,
         string $contentType = self::contentTypes['testQueryDatetimeDateString'][0]
     ): PromiseInterface
     {
@@ -744,9 +744,9 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryDatetimeDateStringRequest(
-        $datetime_query = null,
-        $date_query = null,
-        $string_query = null,
+        ?\DateTime $datetime_query = null,
+        ?\DateTime $date_query = null,
+        ?string $string_query = null,
         string $contentType = self::contentTypes['testQueryDatetimeDateString'][0]
     ): Request
     {
@@ -1045,9 +1045,9 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testQueryIntegerBooleanStringAsyncWithHttpInfo(
-        $integer_query = null,
-        $boolean_query = null,
-        $string_query = null,
+        ?int $integer_query = null,
+        ?bool $boolean_query = null,
+        ?string $string_query = null,
         string $contentType = self::contentTypes['testQueryIntegerBooleanString'][0]
     ): PromiseInterface
     {
@@ -1102,9 +1102,9 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryIntegerBooleanStringRequest(
-        $integer_query = null,
-        $boolean_query = null,
-        $string_query = null,
+        ?int $integer_query = null,
+        ?bool $boolean_query = null,
+        ?string $string_query = null,
         string $contentType = self::contentTypes['testQueryIntegerBooleanString'][0]
     ): Request
     {
@@ -1389,7 +1389,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testQueryStyleDeepObjectExplodeTrueObjectAsyncWithHttpInfo(
-        $query_object = null,
+        ?\OpenAPI\Client\Model\Pet $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleDeepObjectExplodeTrueObject'][0]
     ): PromiseInterface
     {
@@ -1442,7 +1442,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryStyleDeepObjectExplodeTrueObjectRequest(
-        $query_object = null,
+        ?\OpenAPI\Client\Model\Pet $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleDeepObjectExplodeTrueObject'][0]
     ): Request
     {
@@ -1707,7 +1707,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testQueryStyleDeepObjectExplodeTrueObjectAllOfAsyncWithHttpInfo(
-        $query_object = null,
+        ?\OpenAPI\Client\Model\TestQueryStyleDeepObjectExplodeTrueObjectAllOfQueryObjectParameter $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleDeepObjectExplodeTrueObjectAllOf'][0]
     ): PromiseInterface
     {
@@ -1760,7 +1760,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryStyleDeepObjectExplodeTrueObjectAllOfRequest(
-        $query_object = null,
+        ?\OpenAPI\Client\Model\TestQueryStyleDeepObjectExplodeTrueObjectAllOfQueryObjectParameter $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleDeepObjectExplodeTrueObjectAllOf'][0]
     ): Request
     {
@@ -1853,7 +1853,7 @@ public function testQueryStyleDeepObjectExplodeTrueObjectAllOfRequest(
      * @return string
      */
     public function testQueryStyleFormExplodeFalseArrayInteger(
-        ?array $query_object = null,
+        array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayInteger'][0]
     ): string
     {
@@ -1874,7 +1874,7 @@ public function testQueryStyleFormExplodeFalseArrayInteger(
      * @return array of string, HTTP status code, HTTP response headers (array of strings)
      */
     public function testQueryStyleFormExplodeFalseArrayIntegerWithHttpInfo(
-        ?array $query_object = null,
+        array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayInteger'][0]
     ): array
     {
@@ -2001,7 +2001,7 @@ public function testQueryStyleFormExplodeFalseArrayIntegerWithHttpInfo(
      * @return PromiseInterface
      */
     public function testQueryStyleFormExplodeFalseArrayIntegerAsync(
-        ?array $query_object = null,
+        array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayInteger'][0]
     ): PromiseInterface
     {
@@ -2025,7 +2025,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testQueryStyleFormExplodeFalseArrayIntegerAsyncWithHttpInfo(
-        $query_object = null,
+        array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayInteger'][0]
     ): PromiseInterface
     {
@@ -2078,7 +2078,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryStyleFormExplodeFalseArrayIntegerRequest(
-        $query_object = null,
+        array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayInteger'][0]
     ): Request
     {
@@ -2171,7 +2171,7 @@ public function testQueryStyleFormExplodeFalseArrayIntegerRequest(
      * @return string
      */
     public function testQueryStyleFormExplodeFalseArrayString(
-        ?array $query_object = null,
+        array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayString'][0]
     ): string
     {
@@ -2192,7 +2192,7 @@ public function testQueryStyleFormExplodeFalseArrayString(
      * @return array of string, HTTP status code, HTTP response headers (array of strings)
      */
     public function testQueryStyleFormExplodeFalseArrayStringWithHttpInfo(
-        ?array $query_object = null,
+        array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayString'][0]
     ): array
     {
@@ -2319,7 +2319,7 @@ public function testQueryStyleFormExplodeFalseArrayStringWithHttpInfo(
      * @return PromiseInterface
      */
     public function testQueryStyleFormExplodeFalseArrayStringAsync(
-        ?array $query_object = null,
+        array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayString'][0]
     ): PromiseInterface
     {
@@ -2343,7 +2343,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testQueryStyleFormExplodeFalseArrayStringAsyncWithHttpInfo(
-        $query_object = null,
+        array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayString'][0]
     ): PromiseInterface
     {
@@ -2396,7 +2396,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryStyleFormExplodeFalseArrayStringRequest(
-        $query_object = null,
+        array $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeFalseArrayString'][0]
     ): Request
     {
@@ -2661,7 +2661,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testQueryStyleFormExplodeTrueArrayStringAsyncWithHttpInfo(
-        $query_object = null,
+        ?\OpenAPI\Client\Model\TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeTrueArrayString'][0]
     ): PromiseInterface
     {
@@ -2714,7 +2714,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryStyleFormExplodeTrueArrayStringRequest(
-        $query_object = null,
+        ?\OpenAPI\Client\Model\TestQueryStyleFormExplodeTrueArrayStringQueryObjectParameter $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeTrueArrayString'][0]
     ): Request
     {
@@ -2979,7 +2979,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testQueryStyleFormExplodeTrueObjectAsyncWithHttpInfo(
-        $query_object = null,
+        ?\OpenAPI\Client\Model\Pet $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeTrueObject'][0]
     ): PromiseInterface
     {
@@ -3032,7 +3032,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryStyleFormExplodeTrueObjectRequest(
-        $query_object = null,
+        ?\OpenAPI\Client\Model\Pet $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeTrueObject'][0]
     ): Request
     {
@@ -3297,7 +3297,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testQueryStyleFormExplodeTrueObjectAllOfAsyncWithHttpInfo(
-        $query_object = null,
+        ?\OpenAPI\Client\Model\DataQuery $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeTrueObjectAllOf'][0]
     ): PromiseInterface
     {
@@ -3350,7 +3350,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryStyleFormExplodeTrueObjectAllOfRequest(
-        $query_object = null,
+        ?\OpenAPI\Client\Model\DataQuery $query_object = null,
         string $contentType = self::contentTypes['testQueryStyleFormExplodeTrueObjectAllOf'][0]
     ): Request
     {
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/AnotherFakeApi.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/AnotherFakeApi.php
index 0bbfa21ae735..08e9ac3c352c 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/AnotherFakeApi.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/AnotherFakeApi.php
@@ -307,7 +307,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function call123TestSpecialTagsAsyncWithHttpInfo(
-        $client,
+        \OpenAPI\Client\Model\Client $client,
         string $contentType = self::contentTypes['call123TestSpecialTags'][0]
     ): PromiseInterface
     {
@@ -360,7 +360,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function call123TestSpecialTagsRequest(
-        $client,
+        \OpenAPI\Client\Model\Client $client,
         string $contentType = self::contentTypes['call123TestSpecialTags'][0]
     ): Request
     {
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/FakeApi.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/FakeApi.php
index 2ae29d84e293..e489439ba148 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/FakeApi.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/FakeApi.php
@@ -678,9 +678,9 @@ function ($response) {
      * @return PromiseInterface
      */
     public function fakeEnumEndpointAsyncWithHttpInfo(
-        $enum_class,
-        $enum_class_array,
-        $enum_class_map,
+        \OpenAPI\Client\Model\EnumClass $enum_class,
+        array $enum_class_array,
+        array $enum_class_map,
         string $contentType = self::contentTypes['fakeEnumEndpoint'][0]
     ): PromiseInterface
     {
@@ -735,9 +735,9 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function fakeEnumEndpointRequest(
-        $enum_class,
-        $enum_class_array,
-        $enum_class_map,
+        \OpenAPI\Client\Model\EnumClass $enum_class,
+        array $enum_class_array,
+        array $enum_class_map,
         string $contentType = self::contentTypes['fakeEnumEndpoint'][0]
     ): Request
     {
@@ -1274,9 +1274,9 @@ function ($response) {
      * @return PromiseInterface
      */
     public function fakeHttpSignatureTestAsyncWithHttpInfo(
-        $pet,
-        $query_1 = null,
-        $header_1 = null,
+        \OpenAPI\Client\Model\Pet $pet,
+        ?string $query_1 = null,
+        ?string $header_1 = null,
         string $contentType = self::contentTypes['fakeHttpSignatureTest'][0]
     ): PromiseInterface
     {
@@ -1318,9 +1318,9 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function fakeHttpSignatureTestRequest(
-        $pet,
-        $query_1 = null,
-        $header_1 = null,
+        \OpenAPI\Client\Model\Pet $pet,
+        ?string $query_1 = null,
+        ?string $header_1 = null,
         string $contentType = self::contentTypes['fakeHttpSignatureTest'][0]
     ): Request
     {
@@ -1596,7 +1596,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function fakeOuterBooleanSerializeAsyncWithHttpInfo(
-        $body = null,
+        ?bool $body = null,
         string $contentType = self::contentTypes['fakeOuterBooleanSerialize'][0]
     ): PromiseInterface
     {
@@ -1649,7 +1649,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function fakeOuterBooleanSerializeRequest(
-        $body = null,
+        ?bool $body = null,
         string $contentType = self::contentTypes['fakeOuterBooleanSerialize'][0]
     ): Request
     {
@@ -1904,7 +1904,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function fakeOuterCompositeSerializeAsyncWithHttpInfo(
-        $outer_composite = null,
+        ?\OpenAPI\Client\Model\OuterComposite $outer_composite = null,
         string $contentType = self::contentTypes['fakeOuterCompositeSerialize'][0]
     ): PromiseInterface
     {
@@ -1957,7 +1957,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function fakeOuterCompositeSerializeRequest(
-        $outer_composite = null,
+        ?\OpenAPI\Client\Model\OuterComposite $outer_composite = null,
         string $contentType = self::contentTypes['fakeOuterCompositeSerialize'][0]
     ): Request
     {
@@ -2212,7 +2212,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function fakeOuterNumberSerializeAsyncWithHttpInfo(
-        $body = null,
+        ?float $body = null,
         string $contentType = self::contentTypes['fakeOuterNumberSerialize'][0]
     ): PromiseInterface
     {
@@ -2265,7 +2265,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function fakeOuterNumberSerializeRequest(
-        $body = null,
+        ?float $body = null,
         string $contentType = self::contentTypes['fakeOuterNumberSerialize'][0]
     ): Request
     {
@@ -2520,7 +2520,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function fakeOuterStringSerializeAsyncWithHttpInfo(
-        $body = null,
+        ?string $body = null,
         string $contentType = self::contentTypes['fakeOuterStringSerialize'][0]
     ): PromiseInterface
     {
@@ -2573,7 +2573,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function fakeOuterStringSerializeRequest(
-        $body = null,
+        ?string $body = null,
         string $contentType = self::contentTypes['fakeOuterStringSerialize'][0]
     ): Request
     {
@@ -2828,7 +2828,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function fakePropertyEnumIntegerSerializeAsyncWithHttpInfo(
-        $outer_object_with_enum_property,
+        \OpenAPI\Client\Model\OuterObjectWithEnumProperty $outer_object_with_enum_property,
         string $contentType = self::contentTypes['fakePropertyEnumIntegerSerialize'][0]
     ): PromiseInterface
     {
@@ -2881,7 +2881,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function fakePropertyEnumIntegerSerializeRequest(
-        $outer_object_with_enum_property,
+        \OpenAPI\Client\Model\OuterObjectWithEnumProperty $outer_object_with_enum_property,
         string $contentType = self::contentTypes['fakePropertyEnumIntegerSerialize'][0]
     ): Request
     {
@@ -3072,7 +3072,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testAdditionalPropertiesReferenceAsyncWithHttpInfo(
-        $request_body,
+        array $request_body,
         string $contentType = self::contentTypes['testAdditionalPropertiesReference'][0]
     ): PromiseInterface
     {
@@ -3112,7 +3112,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testAdditionalPropertiesReferenceRequest(
-        $request_body,
+        array $request_body,
         string $contentType = self::contentTypes['testAdditionalPropertiesReference'][0]
     ): Request
     {
@@ -3207,7 +3207,7 @@ public function testAdditionalPropertiesReferenceRequest(
      * @return void
      */
     public function testBodyWithBinary(
-        \SplFileObject $body,
+        ?\SplFileObject $body,
         string $contentType = self::contentTypes['testBodyWithBinary'][0]
     ): void
     {
@@ -3225,7 +3225,7 @@ public function testBodyWithBinary(
      * @return array of null, HTTP status code, HTTP response headers (array of strings)
      */
     public function testBodyWithBinaryWithHttpInfo(
-        \SplFileObject $body,
+        ?\SplFileObject $body,
         string $contentType = self::contentTypes['testBodyWithBinary'][0]
     ): array
     {
@@ -3273,7 +3273,7 @@ public function testBodyWithBinaryWithHttpInfo(
      * @return PromiseInterface
      */
     public function testBodyWithBinaryAsync(
-        \SplFileObject $body,
+        ?\SplFileObject $body,
         string $contentType = self::contentTypes['testBodyWithBinary'][0]
     ): PromiseInterface
     {
@@ -3295,7 +3295,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testBodyWithBinaryAsyncWithHttpInfo(
-        $body,
+        ?\SplFileObject $body,
         string $contentType = self::contentTypes['testBodyWithBinary'][0]
     ): PromiseInterface
     {
@@ -3335,7 +3335,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testBodyWithBinaryRequest(
-        $body,
+        ?\SplFileObject $body,
         string $contentType = self::contentTypes['testBodyWithBinary'][0]
     ): Request
     {
@@ -3518,7 +3518,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testBodyWithFileSchemaAsyncWithHttpInfo(
-        $file_schema_test_class,
+        \OpenAPI\Client\Model\FileSchemaTestClass $file_schema_test_class,
         string $contentType = self::contentTypes['testBodyWithFileSchema'][0]
     ): PromiseInterface
     {
@@ -3558,7 +3558,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testBodyWithFileSchemaRequest(
-        $file_schema_test_class,
+        \OpenAPI\Client\Model\FileSchemaTestClass $file_schema_test_class,
         string $contentType = self::contentTypes['testBodyWithFileSchema'][0]
     ): Request
     {
@@ -3748,8 +3748,8 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testBodyWithQueryParamsAsyncWithHttpInfo(
-        $query,
-        $user,
+        string $query,
+        \OpenAPI\Client\Model\User $user,
         string $contentType = self::contentTypes['testBodyWithQueryParams'][0]
     ): PromiseInterface
     {
@@ -3790,8 +3790,8 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testBodyWithQueryParamsRequest(
-        $query,
-        $user,
+        string $query,
+        \OpenAPI\Client\Model\User $user,
         string $contentType = self::contentTypes['testBodyWithQueryParams'][0]
     ): Request
     {
@@ -4076,7 +4076,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testClientModelAsyncWithHttpInfo(
-        $client,
+        \OpenAPI\Client\Model\Client $client,
         string $contentType = self::contentTypes['testClientModel'][0]
     ): PromiseInterface
     {
@@ -4129,7 +4129,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testClientModelRequest(
-        $client,
+        \OpenAPI\Client\Model\Client $client,
         string $contentType = self::contentTypes['testClientModel'][0]
     ): Request
     {
@@ -4411,20 +4411,20 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testEndpointParametersAsyncWithHttpInfo(
-        $number,
-        $double,
-        $pattern_without_delimiter,
-        $byte,
-        $integer = null,
-        $int32 = null,
-        $int64 = null,
-        $float = null,
-        $string = null,
-        $binary = null,
-        $date = null,
-        $date_time = null,
-        $password = null,
-        $callback = null,
+        float $number,
+        float $double,
+        string $pattern_without_delimiter,
+        string $byte,
+        ?int $integer = null,
+        ?int $int32 = null,
+        ?int $int64 = null,
+        ?float $float = null,
+        ?string $string = null,
+        ?\SplFileObject $binary = null,
+        ?\DateTime $date = null,
+        ?\DateTime $date_time = null,
+        ?string $password = null,
+        ?string $callback = null,
         string $contentType = self::contentTypes['testEndpointParameters'][0]
     ): PromiseInterface
     {
@@ -4477,20 +4477,20 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testEndpointParametersRequest(
-        $number,
-        $double,
-        $pattern_without_delimiter,
-        $byte,
-        $integer = null,
-        $int32 = null,
-        $int64 = null,
-        $float = null,
-        $string = null,
-        $binary = null,
-        $date = null,
-        $date_time = null,
-        $password = null,
-        $callback = null,
+        float $number,
+        float $double,
+        string $pattern_without_delimiter,
+        string $byte,
+        ?int $integer = null,
+        ?int $int32 = null,
+        ?int $int64 = null,
+        ?float $float = null,
+        ?string $string = null,
+        ?\SplFileObject $binary = null,
+        ?\DateTime $date = null,
+        ?\DateTime $date_time = null,
+        ?string $password = null,
+        ?string $callback = null,
         string $contentType = self::contentTypes['testEndpointParameters'][0]
     ): Request
     {
@@ -4728,14 +4728,14 @@ public function testEndpointParametersRequest(
      * @return void
      */
     public function testEnumParameters(
-        ?array $enum_header_string_array = ['$'],
+        array $enum_header_string_array = ['$'],
         ?string $enum_header_string = '-efg',
-        ?array $enum_query_string_array = ['$'],
+        array $enum_query_string_array = ['$'],
         ?string $enum_query_string = '-efg',
         ?int $enum_query_integer = null,
         ?float $enum_query_double = null,
-        ?array $enum_query_model_array = null,
-        ?array $enum_form_string_array = ['$'],
+        array $enum_query_model_array = null,
+        array $enum_form_string_array = ['$'],
         ?string $enum_form_string = '-efg',
         string $contentType = self::contentTypes['testEnumParameters'][0]
     ): void
@@ -4764,14 +4764,14 @@ public function testEnumParameters(
      * @return array of null, HTTP status code, HTTP response headers (array of strings)
      */
     public function testEnumParametersWithHttpInfo(
-        ?array $enum_header_string_array = ['$'],
+        array $enum_header_string_array = ['$'],
         ?string $enum_header_string = '-efg',
-        ?array $enum_query_string_array = ['$'],
+        array $enum_query_string_array = ['$'],
         ?string $enum_query_string = '-efg',
         ?int $enum_query_integer = null,
         ?float $enum_query_double = null,
-        ?array $enum_query_model_array = null,
-        ?array $enum_form_string_array = ['$'],
+        array $enum_query_model_array = null,
+        array $enum_form_string_array = ['$'],
         ?string $enum_form_string = '-efg',
         string $contentType = self::contentTypes['testEnumParameters'][0]
     ): array
@@ -4830,14 +4830,14 @@ public function testEnumParametersWithHttpInfo(
      * @return PromiseInterface
      */
     public function testEnumParametersAsync(
-        ?array $enum_header_string_array = ['$'],
+        array $enum_header_string_array = ['$'],
         ?string $enum_header_string = '-efg',
-        ?array $enum_query_string_array = ['$'],
+        array $enum_query_string_array = ['$'],
         ?string $enum_query_string = '-efg',
         ?int $enum_query_integer = null,
         ?float $enum_query_double = null,
-        ?array $enum_query_model_array = null,
-        ?array $enum_form_string_array = ['$'],
+        array $enum_query_model_array = null,
+        array $enum_form_string_array = ['$'],
         ?string $enum_form_string = '-efg',
         string $contentType = self::contentTypes['testEnumParameters'][0]
     ): PromiseInterface
@@ -4870,15 +4870,15 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testEnumParametersAsyncWithHttpInfo(
-        $enum_header_string_array = ['$'],
-        $enum_header_string = '-efg',
-        $enum_query_string_array = ['$'],
-        $enum_query_string = '-efg',
-        $enum_query_integer = null,
-        $enum_query_double = null,
-        $enum_query_model_array = null,
-        $enum_form_string_array = ['$'],
-        $enum_form_string = '-efg',
+        array $enum_header_string_array = ['$'],
+        ?string $enum_header_string = '-efg',
+        array $enum_query_string_array = ['$'],
+        ?string $enum_query_string = '-efg',
+        ?int $enum_query_integer = null,
+        ?float $enum_query_double = null,
+        array $enum_query_model_array = null,
+        array $enum_form_string_array = ['$'],
+        ?string $enum_form_string = '-efg',
         string $contentType = self::contentTypes['testEnumParameters'][0]
     ): PromiseInterface
     {
@@ -4926,15 +4926,15 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testEnumParametersRequest(
-        $enum_header_string_array = ['$'],
-        $enum_header_string = '-efg',
-        $enum_query_string_array = ['$'],
-        $enum_query_string = '-efg',
-        $enum_query_integer = null,
-        $enum_query_double = null,
-        $enum_query_model_array = null,
-        $enum_form_string_array = ['$'],
-        $enum_form_string = '-efg',
+        array $enum_header_string_array = ['$'],
+        ?string $enum_header_string = '-efg',
+        array $enum_query_string_array = ['$'],
+        ?string $enum_query_string = '-efg',
+        ?int $enum_query_integer = null,
+        ?float $enum_query_double = null,
+        array $enum_query_model_array = null,
+        array $enum_form_string_array = ['$'],
+        ?string $enum_form_string = '-efg',
         string $contentType = self::contentTypes['testEnumParameters'][0]
     ): Request
     {
@@ -5511,7 +5511,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testInlineAdditionalPropertiesAsyncWithHttpInfo(
-        $request_body,
+        array $request_body,
         string $contentType = self::contentTypes['testInlineAdditionalProperties'][0]
     ): PromiseInterface
     {
@@ -5551,7 +5551,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testInlineAdditionalPropertiesRequest(
-        $request_body,
+        array $request_body,
         string $contentType = self::contentTypes['testInlineAdditionalProperties'][0]
     ): Request
     {
@@ -5742,7 +5742,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testInlineFreeformAdditionalPropertiesAsyncWithHttpInfo(
-        $test_inline_freeform_additional_properties_request,
+        \OpenAPI\Client\Model\TestInlineFreeformAdditionalPropertiesRequest $test_inline_freeform_additional_properties_request,
         string $contentType = self::contentTypes['testInlineFreeformAdditionalProperties'][0]
     ): PromiseInterface
     {
@@ -5782,7 +5782,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testInlineFreeformAdditionalPropertiesRequest(
-        $test_inline_freeform_additional_properties_request,
+        \OpenAPI\Client\Model\TestInlineFreeformAdditionalPropertiesRequest $test_inline_freeform_additional_properties_request,
         string $contentType = self::contentTypes['testInlineFreeformAdditionalProperties'][0]
     ): Request
     {
@@ -5980,8 +5980,8 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testJsonFormDataAsyncWithHttpInfo(
-        $param,
-        $param2,
+        string $param,
+        string $param2,
         string $contentType = self::contentTypes['testJsonFormData'][0]
     ): PromiseInterface
     {
@@ -6022,8 +6022,8 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testJsonFormDataRequest(
-        $param,
-        $param2,
+        string $param,
+        string $param2,
         string $contentType = self::contentTypes['testJsonFormData'][0]
     ): Request
     {
@@ -6222,7 +6222,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testNullableAsyncWithHttpInfo(
-        $child_with_nullable,
+        \OpenAPI\Client\Model\ChildWithNullable $child_with_nullable,
         string $contentType = self::contentTypes['testNullable'][0]
     ): PromiseInterface
     {
@@ -6262,7 +6262,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testNullableRequest(
-        $child_with_nullable,
+        \OpenAPI\Client\Model\ChildWithNullable $child_with_nullable,
         string $contentType = self::contentTypes['testNullable'][0]
     ): Request
     {
@@ -6369,7 +6369,7 @@ public function testQueryParameterCollectionFormat(
         array $url,
         array $context,
         string $allow_empty,
-        ?array $language = null,
+        array $language = null,
         string $contentType = self::contentTypes['testQueryParameterCollectionFormat'][0]
     ): void
     {
@@ -6399,7 +6399,7 @@ public function testQueryParameterCollectionFormatWithHttpInfo(
         array $url,
         array $context,
         string $allow_empty,
-        ?array $language = null,
+        array $language = null,
         string $contentType = self::contentTypes['testQueryParameterCollectionFormat'][0]
     ): array
     {
@@ -6459,7 +6459,7 @@ public function testQueryParameterCollectionFormatAsync(
         array $url,
         array $context,
         string $allow_empty,
-        ?array $language = null,
+        array $language = null,
         string $contentType = self::contentTypes['testQueryParameterCollectionFormat'][0]
     ): PromiseInterface
     {
@@ -6487,13 +6487,13 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testQueryParameterCollectionFormatAsyncWithHttpInfo(
-        $pipe,
-        $ioutil,
-        $http,
-        $url,
-        $context,
-        $allow_empty,
-        $language = null,
+        array $pipe,
+        array $ioutil,
+        array $http,
+        array $url,
+        array $context,
+        string $allow_empty,
+        array $language = null,
         string $contentType = self::contentTypes['testQueryParameterCollectionFormat'][0]
     ): PromiseInterface
     {
@@ -6539,13 +6539,13 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testQueryParameterCollectionFormatRequest(
-        $pipe,
-        $ioutil,
-        $http,
-        $url,
-        $context,
-        $allow_empty,
-        $language = null,
+        array $pipe,
+        array $ioutil,
+        array $http,
+        array $url,
+        array $context,
+        string $allow_empty,
+        array $language = null,
         string $contentType = self::contentTypes['testQueryParameterCollectionFormat'][0]
     ): Request
     {
@@ -6828,7 +6828,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testStringMapReferenceAsyncWithHttpInfo(
-        $request_body,
+        array $request_body,
         string $contentType = self::contentTypes['testStringMapReference'][0]
     ): PromiseInterface
     {
@@ -6868,7 +6868,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testStringMapReferenceRequest(
-        $request_body,
+        array $request_body,
         string $contentType = self::contentTypes['testStringMapReference'][0]
     ): Request
     {
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/FakeClassnameTags123Api.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/FakeClassnameTags123Api.php
index d6134dd9da28..9ba8235e4ecd 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/FakeClassnameTags123Api.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/FakeClassnameTags123Api.php
@@ -307,7 +307,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function testClassnameAsyncWithHttpInfo(
-        $client,
+        \OpenAPI\Client\Model\Client $client,
         string $contentType = self::contentTypes['testClassname'][0]
     ): PromiseInterface
     {
@@ -360,7 +360,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function testClassnameRequest(
-        $client,
+        \OpenAPI\Client\Model\Client $client,
         string $contentType = self::contentTypes['testClassname'][0]
     ): Request
     {
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/PetApi.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/PetApi.php
index ae7f2413d83d..88fd747f47bf 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/PetApi.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/PetApi.php
@@ -333,7 +333,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function addPetAsyncWithHttpInfo(
-        $pet,
+        \OpenAPI\Client\Model\Pet $pet,
         ?int $hostIndex = null,
         array $variables = [],
         string $contentType = self::contentTypes['addPet'][0]
@@ -393,7 +393,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function addPetRequest(
-        $pet,
+        \OpenAPI\Client\Model\Pet $pet,
         ?int $hostIndex = null,
         array $variables = [],
         string $contentType = self::contentTypes['addPet'][0]
@@ -649,8 +649,8 @@ function ($response) {
      * @return PromiseInterface
      */
     public function deletePetAsyncWithHttpInfo(
-        $pet_id,
-        $api_key = null,
+        int $pet_id,
+        ?string $api_key = null,
         string $contentType = self::contentTypes['deletePet'][0]
     ): PromiseInterface
     {
@@ -691,8 +691,8 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function deletePetRequest(
-        $pet_id,
-        $api_key = null,
+        int $pet_id,
+        ?string $api_key = null,
         string $contentType = self::contentTypes['deletePet'][0]
     ): Request
     {
@@ -971,7 +971,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function findPetsByStatusAsyncWithHttpInfo(
-        $status,
+        array $status,
         string $contentType = self::contentTypes['findPetsByStatus'][0]
     ): PromiseInterface
     {
@@ -1024,7 +1024,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function findPetsByStatusRequest(
-        $status,
+        array $status,
         string $contentType = self::contentTypes['findPetsByStatus'][0]
     ): Request
     {
@@ -1303,7 +1303,7 @@ function ($response) {
      * @deprecated
      */
     public function findPetsByTagsAsyncWithHttpInfo(
-        $tags,
+        array $tags,
         string $contentType = self::contentTypes['findPetsByTags'][0]
     ): PromiseInterface
     {
@@ -1357,7 +1357,7 @@ function ($exception) {
      * @deprecated
      */
     public function findPetsByTagsRequest(
-        $tags,
+        array $tags,
         string $contentType = self::contentTypes['findPetsByTags'][0]
     ): Request
     {
@@ -1632,7 +1632,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function getPetByIdAsyncWithHttpInfo(
-        $pet_id,
+        int $pet_id,
         string $contentType = self::contentTypes['getPetById'][0]
     ): PromiseInterface
     {
@@ -1685,7 +1685,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function getPetByIdRequest(
-        $pet_id,
+        int $pet_id,
         string $contentType = self::contentTypes['getPetById'][0]
     ): Request
     {
@@ -1960,7 +1960,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function updatePetAsyncWithHttpInfo(
-        $pet,
+        \OpenAPI\Client\Model\Pet $pet,
         ?int $hostIndex = null,
         array $variables = [],
         string $contentType = self::contentTypes['updatePet'][0]
@@ -2020,7 +2020,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function updatePetRequest(
-        $pet,
+        \OpenAPI\Client\Model\Pet $pet,
         ?int $hostIndex = null,
         array $variables = [],
         string $contentType = self::contentTypes['updatePet'][0]
@@ -2283,9 +2283,9 @@ function ($response) {
      * @return PromiseInterface
      */
     public function updatePetWithFormAsyncWithHttpInfo(
-        $pet_id,
-        $name = null,
-        $status = null,
+        int $pet_id,
+        ?string $name = null,
+        ?string $status = null,
         string $contentType = self::contentTypes['updatePetWithForm'][0]
     ): PromiseInterface
     {
@@ -2327,9 +2327,9 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function updatePetWithFormRequest(
-        $pet_id,
-        $name = null,
-        $status = null,
+        int $pet_id,
+        ?string $name = null,
+        ?string $status = null,
         string $contentType = self::contentTypes['updatePetWithForm'][0]
     ): Request
     {
@@ -2627,9 +2627,9 @@ function ($response) {
      * @return PromiseInterface
      */
     public function uploadFileAsyncWithHttpInfo(
-        $pet_id,
-        $additional_metadata = null,
-        $file = null,
+        int $pet_id,
+        ?string $additional_metadata = null,
+        ?\SplFileObject $file = null,
         string $contentType = self::contentTypes['uploadFile'][0]
     ): PromiseInterface
     {
@@ -2684,9 +2684,9 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function uploadFileRequest(
-        $pet_id,
-        $additional_metadata = null,
-        $file = null,
+        int $pet_id,
+        ?string $additional_metadata = null,
+        ?\SplFileObject $file = null,
         string $contentType = self::contentTypes['uploadFile'][0]
     ): Request
     {
@@ -2994,9 +2994,9 @@ function ($response) {
      * @return PromiseInterface
      */
     public function uploadFileWithRequiredFileAsyncWithHttpInfo(
-        $pet_id,
-        $required_file,
-        $additional_metadata = null,
+        int $pet_id,
+        \SplFileObject $required_file,
+        ?string $additional_metadata = null,
         string $contentType = self::contentTypes['uploadFileWithRequiredFile'][0]
     ): PromiseInterface
     {
@@ -3051,9 +3051,9 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function uploadFileWithRequiredFileRequest(
-        $pet_id,
-        $required_file,
-        $additional_metadata = null,
+        int $pet_id,
+        \SplFileObject $required_file,
+        ?string $additional_metadata = null,
         string $contentType = self::contentTypes['uploadFileWithRequiredFile'][0]
     ): Request
     {
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/StoreApi.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/StoreApi.php
index 99afa3b09938..892670b58247 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/StoreApi.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/StoreApi.php
@@ -238,7 +238,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function deleteOrderAsyncWithHttpInfo(
-        $order_id,
+        string $order_id,
         string $contentType = self::contentTypes['deleteOrder'][0]
     ): PromiseInterface
     {
@@ -278,7 +278,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function deleteOrderRequest(
-        $order_id,
+        string $order_id,
         string $contentType = self::contentTypes['deleteOrder'][0]
     ): Request
     {
@@ -851,7 +851,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function getOrderByIdAsyncWithHttpInfo(
-        $order_id,
+        int $order_id,
         string $contentType = self::contentTypes['getOrderById'][0]
     ): PromiseInterface
     {
@@ -904,7 +904,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function getOrderByIdRequest(
-        $order_id,
+        int $order_id,
         string $contentType = self::contentTypes['getOrderById'][0]
     ): Request
     {
@@ -1180,7 +1180,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function placeOrderAsyncWithHttpInfo(
-        $order,
+        \OpenAPI\Client\Model\Order $order,
         string $contentType = self::contentTypes['placeOrder'][0]
     ): PromiseInterface
     {
@@ -1233,7 +1233,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function placeOrderRequest(
-        $order,
+        \OpenAPI\Client\Model\Order $order,
         string $contentType = self::contentTypes['placeOrder'][0]
     ): Request
     {
diff --git a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/UserApi.php b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/UserApi.php
index 8181e112fdec..e7eb2ab78a33 100644
--- a/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/UserApi.php
+++ b/samples/client/petstore/php-nextgen/OpenAPIClient-php/src/Api/UserApi.php
@@ -250,7 +250,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function createUserAsyncWithHttpInfo(
-        $user,
+        \OpenAPI\Client\Model\User $user,
         string $contentType = self::contentTypes['createUser'][0]
     ): PromiseInterface
     {
@@ -290,7 +290,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function createUserRequest(
-        $user,
+        \OpenAPI\Client\Model\User $user,
         string $contentType = self::contentTypes['createUser'][0]
     ): Request
     {
@@ -481,7 +481,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function createUsersWithArrayInputAsyncWithHttpInfo(
-        $user,
+        array $user,
         string $contentType = self::contentTypes['createUsersWithArrayInput'][0]
     ): PromiseInterface
     {
@@ -521,7 +521,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function createUsersWithArrayInputRequest(
-        $user,
+        array $user,
         string $contentType = self::contentTypes['createUsersWithArrayInput'][0]
     ): Request
     {
@@ -712,7 +712,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function createUsersWithListInputAsyncWithHttpInfo(
-        $user,
+        array $user,
         string $contentType = self::contentTypes['createUsersWithListInput'][0]
     ): PromiseInterface
     {
@@ -752,7 +752,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function createUsersWithListInputRequest(
-        $user,
+        array $user,
         string $contentType = self::contentTypes['createUsersWithListInput'][0]
     ): Request
     {
@@ -943,7 +943,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function deleteUserAsyncWithHttpInfo(
-        $username,
+        string $username,
         string $contentType = self::contentTypes['deleteUser'][0]
     ): PromiseInterface
     {
@@ -983,7 +983,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function deleteUserRequest(
-        $username,
+        string $username,
         string $contentType = self::contentTypes['deleteUser'][0]
     ): Request
     {
@@ -1253,7 +1253,7 @@ function ($response) {
      * @return PromiseInterface
      */
     public function getUserByNameAsyncWithHttpInfo(
-        $username,
+        string $username,
         string $contentType = self::contentTypes['getUserByName'][0]
     ): PromiseInterface
     {
@@ -1306,7 +1306,7 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function getUserByNameRequest(
-        $username,
+        string $username,
         string $contentType = self::contentTypes['getUserByName'][0]
     ): Request
     {
@@ -1583,8 +1583,8 @@ function ($response) {
      * @return PromiseInterface
      */
     public function loginUserAsyncWithHttpInfo(
-        $username,
-        $password,
+        string $username,
+        string $password,
         string $contentType = self::contentTypes['loginUser'][0]
     ): PromiseInterface
     {
@@ -1638,8 +1638,8 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function loginUserRequest(
-        $username,
-        $password,
+        string $username,
+        string $password,
         string $contentType = self::contentTypes['loginUser'][0]
     ): Request
     {
@@ -2062,8 +2062,8 @@ function ($response) {
      * @return PromiseInterface
      */
     public function updateUserAsyncWithHttpInfo(
-        $username,
-        $user,
+        string $username,
+        \OpenAPI\Client\Model\User $user,
         string $contentType = self::contentTypes['updateUser'][0]
     ): PromiseInterface
     {
@@ -2104,8 +2104,8 @@ function ($exception) {
      * @return \GuzzleHttp\Psr7\Request
      */
     public function updateUserRequest(
-        $username,
-        $user,
+        string $username,
+        \OpenAPI\Client\Model\User $user,
         string $contentType = self::contentTypes['updateUser'][0]
     ): Request
     {