diff --git a/bin/configs/kotlin-gson.yaml b/bin/configs/kotlin-gson.yaml
index e4e55689509d..8e6eccccbd49 100644
--- a/bin/configs/kotlin-gson.yaml
+++ b/bin/configs/kotlin-gson.yaml
@@ -1,7 +1,8 @@
 generatorName: kotlin
 outputDir: samples/client/petstore/kotlin-gson
-inputSpec: modules/openapi-generator/src/test/resources/2_0/petstore.yaml
+inputSpec: modules/openapi-generator/src/test/resources/3_0/petstore.yaml
 templateDir: modules/openapi-generator/src/main/resources/kotlin-client
 additionalProperties:
   serializationLibrary: gson
   artifactId: kotlin-petstore-gson
+  companionObject: true
diff --git a/docs/generators/kotlin-spring.md b/docs/generators/kotlin-spring.md
index a169cb0b7e83..ab39d3a2942a 100644
--- a/docs/generators/kotlin-spring.md
+++ b/docs/generators/kotlin-spring.md
@@ -27,6 +27,7 @@ These options may be applied as additional-properties (cli) or configOptions (pl
 |autoXSpringPaginated|Automatically add x-spring-paginated to operations that have 'page', 'size', and 'sort' query parameters. When enabled, operations with all three parameters will have Pageable support automatically applied. Operations with x-spring-paginated explicitly set to false will not be auto-detected.| |false|
 |basePackage|base package (invokerPackage) for generated code| |org.openapitools|
 |beanQualifiers|Whether to add fully-qualifier class names as bean qualifiers in @Component and @RestController annotations. May be used to prevent bean names clash if multiple generated libraries (contexts) added to single project.| |false|
+|companionObject|Whether to generate companion objects in data classes, enabling companion extensions.| |false|
 |configPackage|configuration package for generated code| |org.openapitools.configuration|
 |declarativeInterfaceReactiveMode|What type of reactive style to use in Spring Http declarative interface|<dl><dt>**coroutines**</dt><dd>Use kotlin-idiomatic 'suspend' functions</dd><dt>**reactor**</dt><dd>Use reactor return wrappers 'Mono' and 'Flux'</dd></dl>|coroutines|
 |delegatePattern|Whether to generate the server files using the delegate pattern| |false|
diff --git a/docs/generators/kotlin.md b/docs/generators/kotlin.md
index 5c1a70330b6e..22b931b9229e 100644
--- a/docs/generators/kotlin.md
+++ b/docs/generators/kotlin.md
@@ -23,6 +23,7 @@ These options may be applied as additional-properties (cli) or configOptions (pl
 |artifactId|Generated artifact id (name of jar).| |kotlin-client|
 |artifactVersion|Generated artifact's package version.| |1.0.0|
 |collectionType|Option. Collection type to use|<dl><dt>**array**</dt><dd>kotlin.Array</dd><dt>**list**</dt><dd>kotlin.collections.List</dd></dl>|list|
+|companionObject|Whether to generate companion objects in data classes, enabling companion extensions.| |false|
 |dateLibrary|Option. Date library to use|<dl><dt>**threetenbp-localdatetime**</dt><dd>Threetenbp - Backport of JSR310 (jvm only, for legacy app only)</dd><dt>**kotlinx-datetime**</dt><dd>kotlinx-datetime (preferred for multiplatform)</dd><dt>**string**</dt><dd>String</dd><dt>**java8-localdatetime**</dt><dd>Java 8 native JSR310 (jvm only, for legacy app only)</dd><dt>**java8**</dt><dd>Java 8 native JSR310 (jvm only, preferred for jdk 1.8+)</dd><dt>**threetenbp**</dt><dd>Threetenbp - Backport of JSR310 (jvm only, preferred for jdk &lt; 1.8)</dd></dl>|java8|
 |enumPropertyNaming|Naming convention for enum properties: 'camelCase', 'PascalCase', 'snake_case', 'UPPERCASE', and 'original'| |original|
 |explicitApi|Generates code with explicit access modifiers to comply with Kotlin Explicit API Mode.| |false|
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinClientCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinClientCodegen.java
index e0b51976ce5c..57b5f20dbcd9 100755
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinClientCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinClientCodegen.java
@@ -106,6 +106,8 @@ public class KotlinClientCodegen extends AbstractKotlinCodegen {
 
     public static final String GENERATE_ONEOF_ANYOF_WRAPPERS = "generateOneOfAnyOfWrappers";
 
+    public static final String COMPANION_OBJECT = "companionObject";
+
     protected static final String VENDOR_EXTENSION_BASE_NAME_LITERAL = "x-base-name-literal";
 
 
@@ -123,6 +125,7 @@ public class KotlinClientCodegen extends AbstractKotlinCodegen {
     @Setter protected boolean mapFileBinaryToByteArray = false;
     @Setter protected boolean generateOneOfAnyOfWrappers = true;
     @Getter @Setter protected boolean failOnUnknownProperties = false;
+    @Setter protected boolean companionObject = false;
 
     protected String authFolder;
 
@@ -288,6 +291,8 @@ public KotlinClientCodegen() {
 
         cliOptions.add(CliOption.newBoolean(GENERATE_ONEOF_ANYOF_WRAPPERS, "Generate oneOf, anyOf schemas as wrappers. Only `jvm-retrofit2`(library) with `gson` or `kotlinx_serialization`(serializationLibrary) support this option."));
 
+        cliOptions.add(CliOption.newBoolean(COMPANION_OBJECT, "Whether to generate companion objects in data classes, enabling companion extensions.", false));
+
         CliOption serializationLibraryOpt = new CliOption(CodegenConstants.SERIALIZATION_LIBRARY, SERIALIZATION_LIBRARY_DESC);
         cliOptions.add(serializationLibraryOpt.defaultValue(serializationLibrary.name()));
 
@@ -322,6 +327,10 @@ public boolean getGenerateOneOfAnyOfWrappers() {
         return generateOneOfAnyOfWrappers;
     }
 
+    public boolean getCompanionObject() {
+        return companionObject;
+    }
+
     public void setGenerateRoomModels(Boolean generateRoomModels) {
         this.generateRoomModels = generateRoomModels;
     }
@@ -484,6 +493,12 @@ public void processOpts() {
             setFailOnUnknownProperties(false);
         }
 
+        if (additionalProperties.containsKey(COMPANION_OBJECT)) {
+            setCompanionObject(convertPropertyToBooleanAndWriteBack(COMPANION_OBJECT));
+        } else {
+            additionalProperties.put(COMPANION_OBJECT, companionObject);
+        }
+
         commonSupportingFiles();
 
         switch (getLibrary()) {
@@ -936,7 +951,7 @@ public ModelsMap postProcessModels(ModelsMap objs) {
 
         for (ModelMap mo : objects.getModels()) {
             CodegenModel cm = mo.getModel();
-            if (getGenerateRoomModels() || getGenerateOneOfAnyOfWrappers()) {
+            if (getGenerateRoomModels() || getGenerateOneOfAnyOfWrappers() || getCompanionObject()) {
                 cm.vendorExtensions.put("x-has-data-class-body", true);
             }
 
diff --git a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinSpringServerCodegen.java b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinSpringServerCodegen.java
index 269075dc780e..1706b802e1f0 100644
--- a/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinSpringServerCodegen.java
+++ b/modules/openapi-generator/src/main/java/org/openapitools/codegen/languages/KotlinSpringServerCodegen.java
@@ -98,6 +98,7 @@ public class KotlinSpringServerCodegen extends AbstractKotlinCodegen
     public static final String USE_REQUEST_MAPPING_ON_INTERFACE = "useRequestMappingOnInterface";
     public static final String AUTO_X_SPRING_PAGINATED = "autoXSpringPaginated";
     public static final String USE_SEALED_RESPONSE_INTERFACES = "useSealedResponseInterfaces";
+    public static final String COMPANION_OBJECT = "companionObject";
 
     @Getter
     public enum DeclarativeInterfaceReactiveMode {
@@ -163,6 +164,7 @@ public String getDescription() {
     @Setter private boolean useResponseEntity = true;
     @Setter private boolean autoXSpringPaginated = false;
     @Setter private boolean useSealedResponseInterfaces = false;
+    @Setter private boolean companionObject = false;
 
     @Getter @Setter
     protected boolean useSpringBoot3 = false;
@@ -265,6 +267,7 @@ public KotlinSpringServerCodegen() {
         addOption(SCHEMA_IMPLEMENTS, "A map of single interface or a list of interfaces per schema name that should be implemented (serves similar purpose as `x-kotlin-implements`, but is fully decoupled from the api spec). Example: yaml `schemaImplements: {Pet: com.some.pack.WithId, Category: [com.some.pack.CategoryInterface], Dog: [com.some.pack.Canine, com.some.pack.OtherInterface]}` implements interfaces in schemas `Pet` (interface `com.some.pack.WithId`), `Category` (interface `com.some.pack.CategoryInterface`), `Dog`(interfaces `com.some.pack.Canine`, `com.some.pack.OtherInterface`)", "empty map");
         addOption(SCHEMA_IMPLEMENTS_FIELDS, "A map of single field or a list of fields per schema name that should be prepended with `override` (serves similar purpose as `x-kotlin-implements-fields`, but is fully decoupled from the api spec). Example: yaml `schemaImplementsFields: {Pet: id, Category: [name, id], Dog: [bark, breed]}` marks fields to be prepended with `override` in schemas `Pet` (field `id`), `Category` (fields `name`, `id`) and `Dog` (fields `bark`, `breed`)", "empty map");
         addSwitch(AUTO_X_SPRING_PAGINATED, "Automatically add x-spring-paginated to operations that have 'page', 'size', and 'sort' query parameters. When enabled, operations with all three parameters will have Pageable support automatically applied. Operations with x-spring-paginated explicitly set to false will not be auto-detected.", autoXSpringPaginated);
+        addSwitch(COMPANION_OBJECT, "Whether to generate companion objects in data classes, enabling companion extensions.", companionObject);
         supportedLibraries.put(SPRING_BOOT, "Spring-boot Server application.");
         supportedLibraries.put(SPRING_CLOUD_LIBRARY,
                 "Spring-Cloud-Feign client with Spring-Boot auto-configured settings.");
@@ -512,6 +515,12 @@ public void processOpts() {
         }
         writePropertyBack(USE_SEALED_RESPONSE_INTERFACES, useSealedResponseInterfaces);
 
+        if (additionalProperties.containsKey(COMPANION_OBJECT)) {
+            this.setCompanionObject(convertPropertyToBooleanAndWriteBack(COMPANION_OBJECT));
+        } else {
+            additionalProperties.put(COMPANION_OBJECT, companionObject);
+        }
+
         additionalProperties.put("springHttpStatus", new SpringHttpStatusLambda());
 
         // Set basePackage from invokerPackage
diff --git a/modules/openapi-generator/src/main/resources/kotlin-client/data_class.mustache b/modules/openapi-generator/src/main/resources/kotlin-client/data_class.mustache
index b9bb49eae25a..28ec1da04089 100644
--- a/modules/openapi-generator/src/main/resources/kotlin-client/data_class.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-client/data_class.mustache
@@ -123,7 +123,8 @@ import {{packageName}}.infrastructure.ITransformForStorage
         private const val serialVersionUID: Long = 123
     }
 {{/serializableModel}}
-{{#discriminator}}{{#vars}}{{#required}}
+{{^serializableModel}}{{^generateRoomModels}}{{^generateOneOfAnyOfWrappers}}{{#companionObject}}    {{#nonPublicApi}}internal {{/nonPublicApi}}{{^nonPublicApi}}{{#explicitApi}}public {{/explicitApi}}{{/nonPublicApi}}companion object { }
+{{/companionObject}}{{/generateOneOfAnyOfWrappers}}{{/generateRoomModels}}{{/serializableModel}}{{#discriminator}}{{#vars}}{{#required}}
 {{>interface_req_var}}{{/required}}{{^required}}
 {{>interface_opt_var}}{{/required}}{{/vars}}{{/discriminator}}
 {{#hasEnums}}
diff --git a/modules/openapi-generator/src/main/resources/kotlin-spring/dataClass.mustache b/modules/openapi-generator/src/main/resources/kotlin-spring/dataClass.mustache
index 4fadc4b89ccb..178487a26e3b 100644
--- a/modules/openapi-generator/src/main/resources/kotlin-spring/dataClass.mustache
+++ b/modules/openapi-generator/src/main/resources/kotlin-spring/dataClass.mustache
@@ -64,4 +64,5 @@
         private const val serialVersionUID: kotlin.Long = 1
     }
 {{/serializableModel}}
-}
+{{^serializableModel}}{{#companionObject}}    companion object { }
+{{/companionObject}}{{/serializableModel}}}
diff --git a/modules/openapi-generator/src/test/java/org/openapitools/codegen/kotlin/KotlinClientCodegenModelTest.java b/modules/openapi-generator/src/test/java/org/openapitools/codegen/kotlin/KotlinClientCodegenModelTest.java
index 023374b9e248..23f98e3c443e 100644
--- a/modules/openapi-generator/src/test/java/org/openapitools/codegen/kotlin/KotlinClientCodegenModelTest.java
+++ b/modules/openapi-generator/src/test/java/org/openapitools/codegen/kotlin/KotlinClientCodegenModelTest.java
@@ -43,6 +43,7 @@
 import java.util.Map;
 
 import static org.openapitools.codegen.CodegenConstants.*;
+import static org.openapitools.codegen.languages.KotlinClientCodegen.COMPANION_OBJECT;
 import static org.openapitools.codegen.languages.KotlinClientCodegen.GENERATE_ONEOF_ANYOF_WRAPPERS;
 
 @SuppressWarnings("static-method")
@@ -878,6 +879,50 @@ public void emptyModelKotlinxSerializationTest() throws IOException {
         TestUtils.assertFileNotContains(modelKt, "data class EmptyModel");
     }
 
+    @Test
+    public void testCompanionObjectAdditionalProperty() {
+        final KotlinClientCodegen codegen = new KotlinClientCodegen();
+
+        // Default case, nothing provided
+        codegen.processOpts();
+
+        ConfigAssert configAssert = new ConfigAssert(codegen.additionalProperties());
+        // Default to false
+        configAssert.assertValue(COMPANION_OBJECT, codegen::getCompanionObject, Boolean.FALSE);
+
+        // Provide true
+        codegen.additionalProperties().put(COMPANION_OBJECT, true);
+        codegen.processOpts();
+
+        // Should be true
+        configAssert.assertValue(COMPANION_OBJECT, codegen::getCompanionObject, Boolean.TRUE);
+
+        // Provide false
+        codegen.additionalProperties().put(COMPANION_OBJECT, false);
+        codegen.processOpts();
+
+        // Should be false
+        configAssert.assertValue(COMPANION_OBJECT, codegen::getCompanionObject, Boolean.FALSE);
+    }
+
+    @Test
+    public void testCompanionObjectGeneratesCompanionInModel() throws IOException {
+        File output = Files.createTempDirectory("test").toFile();
+        output.deleteOnExit();
+
+        final CodegenConfigurator configurator = new CodegenConfigurator()
+                .setGeneratorName("kotlin")
+                .addAdditionalProperty(COMPANION_OBJECT, true)
+                .setInputSpec("src/test/resources/3_0/petstore.yaml")
+                .setOutputDir(output.getAbsolutePath().replace("\\", "/"));
+
+        DefaultGenerator generator = new DefaultGenerator();
+        generator.opts(configurator.toClientOptInput()).generate();
+
+        Path petModel = Paths.get(output.getAbsolutePath() + "/src/main/kotlin/org/openapitools/client/models/Pet.kt");
+        TestUtils.assertFileContains(petModel, "companion object { }");
+    }
+
     private static class ModelNameTest {
         private final String expectedName;
         private final String expectedClassName;
diff --git a/modules/openapi-generator/src/test/java/org/openapitools/codegen/kotlin/spring/KotlinSpringServerCodegenTest.java b/modules/openapi-generator/src/test/java/org/openapitools/codegen/kotlin/spring/KotlinSpringServerCodegenTest.java
index 9f59e7f2f967..0bdf7f3f128e 100644
--- a/modules/openapi-generator/src/test/java/org/openapitools/codegen/kotlin/spring/KotlinSpringServerCodegenTest.java
+++ b/modules/openapi-generator/src/test/java/org/openapitools/codegen/kotlin/spring/KotlinSpringServerCodegenTest.java
@@ -4706,6 +4706,35 @@ public void testDeprecatedAnnotationOnController() throws IOException {
                 "@Deprecated(message=\"Operation is deprecated\") @RequestMapping("
         );
     }
+
+    @Test
+    public void testCompanionObjectDefaultIsFalse() {
+        final KotlinSpringServerCodegen codegen = new KotlinSpringServerCodegen();
+        codegen.processOpts();
+
+        Assert.assertEquals(codegen.additionalProperties().get(COMPANION_OBJECT), false);
+    }
+
+    @Test
+    public void testCompanionObjectGeneratesCompanionInModel() throws IOException {
+        File output = Files.createTempDirectory("test").toFile().getCanonicalFile();
+        output.deleteOnExit();
+        String outputPath = output.getAbsolutePath().replace('\\', '/');
+
+        KotlinSpringServerCodegen codegen = new KotlinSpringServerCodegen();
+        codegen.setOutputDir(output.getAbsolutePath());
+        codegen.additionalProperties().put(COMPANION_OBJECT, true);
+
+        new DefaultGenerator().opts(new ClientOptInput()
+                        .openAPI(TestUtils.parseSpec("src/test/resources/3_0/petstore.yaml"))
+                        .config(codegen))
+                .generate();
+
+        assertFileContains(
+                Paths.get(outputPath + "/src/main/kotlin/org/openapitools/model/Pet.kt"),
+                "companion object { }"
+        );
+    }
 }
 
 
diff --git a/samples/client/petstore/kotlin-gson/docs/PetApi.md b/samples/client/petstore/kotlin-gson/docs/PetApi.md
index 6856ea516dab..e0bf879c9a65 100644
--- a/samples/client/petstore/kotlin-gson/docs/PetApi.md
+++ b/samples/client/petstore/kotlin-gson/docs/PetApi.md
@@ -16,10 +16,12 @@ All URIs are relative to *http://petstore.swagger.io/v2*
 
 <a id="addPet"></a>
 # **addPet**
-> addPet(body)
+> Pet addPet(pet)
 
 Add a new pet to the store
 
+
+
 ### Example
 ```kotlin
 // Import classes:
@@ -27,9 +29,10 @@ Add a new pet to the store
 //import org.openapitools.client.models.*
 
 val apiInstance = PetApi()
-val body : Pet =  // Pet | Pet object that needs to be added to the store
+val pet : Pet =  // Pet | Pet object that needs to be added to the store
 try {
-    apiInstance.addPet(body)
+    val result : Pet = apiInstance.addPet(pet)
+    println(result)
 } catch (e: ClientException) {
     println("4xx response calling PetApi#addPet")
     e.printStackTrace()
@@ -42,11 +45,11 @@ try {
 ### Parameters
 | Name | Type | Description  | Notes |
 | ------------- | ------------- | ------------- | ------------- |
-| **body** | [**Pet**](Pet.md)| Pet object that needs to be added to the store | |
+| **pet** | [**Pet**](Pet.md)| Pet object that needs to be added to the store | |
 
 ### Return type
 
-null (empty response body)
+[**Pet**](Pet.md)
 
 ### Authorization
 
@@ -57,7 +60,7 @@ Configure petstore_auth:
 ### HTTP request headers
 
  - **Content-Type**: application/json
- - **Accept**: Not defined
+ - **Accept**: application/json
 
 <a id="deletePet"></a>
 # **deletePet**
@@ -65,6 +68,8 @@ Configure petstore_auth:
 
 Deletes a pet
 
+
+
 ### Example
 ```kotlin
 // Import classes:
@@ -253,10 +258,12 @@ Configure api_key:
 
 <a id="updatePet"></a>
 # **updatePet**
-> updatePet(body)
+> Pet updatePet(pet)
 
 Update an existing pet
 
+
+
 ### Example
 ```kotlin
 // Import classes:
@@ -264,9 +271,10 @@ Update an existing pet
 //import org.openapitools.client.models.*
 
 val apiInstance = PetApi()
-val body : Pet =  // Pet | Pet object that needs to be added to the store
+val pet : Pet =  // Pet | Pet object that needs to be added to the store
 try {
-    apiInstance.updatePet(body)
+    val result : Pet = apiInstance.updatePet(pet)
+    println(result)
 } catch (e: ClientException) {
     println("4xx response calling PetApi#updatePet")
     e.printStackTrace()
@@ -279,11 +287,11 @@ try {
 ### Parameters
 | Name | Type | Description  | Notes |
 | ------------- | ------------- | ------------- | ------------- |
-| **body** | [**Pet**](Pet.md)| Pet object that needs to be added to the store | |
+| **pet** | [**Pet**](Pet.md)| Pet object that needs to be added to the store | |
 
 ### Return type
 
-null (empty response body)
+[**Pet**](Pet.md)
 
 ### Authorization
 
@@ -294,7 +302,7 @@ Configure petstore_auth:
 ### HTTP request headers
 
  - **Content-Type**: application/json
- - **Accept**: Not defined
+ - **Accept**: application/json
 
 <a id="updatePetWithForm"></a>
 # **updatePetWithForm**
@@ -302,6 +310,8 @@ Configure petstore_auth:
 
 Updates a pet in the store with form data
 
+
+
 ### Example
 ```kotlin
 // Import classes:
@@ -351,6 +361,8 @@ Configure petstore_auth:
 
 uploads an image
 
+
+
 ### Example
 ```kotlin
 // Import classes:
diff --git a/samples/client/petstore/kotlin-gson/docs/StoreApi.md b/samples/client/petstore/kotlin-gson/docs/StoreApi.md
index 53ff17b16676..bfbf6c75d797 100644
--- a/samples/client/petstore/kotlin-gson/docs/StoreApi.md
+++ b/samples/client/petstore/kotlin-gson/docs/StoreApi.md
@@ -149,10 +149,12 @@ No authorization required
 
 <a id="placeOrder"></a>
 # **placeOrder**
-> Order placeOrder(body)
+> Order placeOrder(order)
 
 Place an order for a pet
 
+
+
 ### Example
 ```kotlin
 // Import classes:
@@ -160,9 +162,9 @@ Place an order for a pet
 //import org.openapitools.client.models.*
 
 val apiInstance = StoreApi()
-val body : Order =  // Order | order placed for purchasing the pet
+val order : Order =  // Order | order placed for purchasing the pet
 try {
-    val result : Order = apiInstance.placeOrder(body)
+    val result : Order = apiInstance.placeOrder(order)
     println(result)
 } catch (e: ClientException) {
     println("4xx response calling StoreApi#placeOrder")
@@ -176,7 +178,7 @@ try {
 ### Parameters
 | Name | Type | Description  | Notes |
 | ------------- | ------------- | ------------- | ------------- |
-| **body** | [**Order**](Order.md)| order placed for purchasing the pet | |
+| **order** | [**Order**](Order.md)| order placed for purchasing the pet | |
 
 ### Return type
 
@@ -188,6 +190,6 @@ No authorization required
 
 ### HTTP request headers
 
- - **Content-Type**: Not defined
+ - **Content-Type**: application/json
  - **Accept**: application/json
 
diff --git a/samples/client/petstore/kotlin-gson/docs/UserApi.md b/samples/client/petstore/kotlin-gson/docs/UserApi.md
index 82c8d6060276..fb5bfa6c7a44 100644
--- a/samples/client/petstore/kotlin-gson/docs/UserApi.md
+++ b/samples/client/petstore/kotlin-gson/docs/UserApi.md
@@ -16,7 +16,7 @@ All URIs are relative to *http://petstore.swagger.io/v2*
 
 <a id="createUser"></a>
 # **createUser**
-> createUser(body)
+> createUser(user)
 
 Create user
 
@@ -29,9 +29,9 @@ This can only be done by the logged in user.
 //import org.openapitools.client.models.*
 
 val apiInstance = UserApi()
-val body : User =  // User | Created user object
+val user : User =  // User | Created user object
 try {
-    apiInstance.createUser(body)
+    apiInstance.createUser(user)
 } catch (e: ClientException) {
     println("4xx response calling UserApi#createUser")
     e.printStackTrace()
@@ -44,7 +44,7 @@ try {
 ### Parameters
 | Name | Type | Description  | Notes |
 | ------------- | ------------- | ------------- | ------------- |
-| **body** | [**User**](User.md)| Created user object | |
+| **user** | [**User**](User.md)| Created user object | |
 
 ### Return type
 
@@ -52,19 +52,24 @@ null (empty response body)
 
 ### Authorization
 
-No authorization required
+
+Configure api_key:
+    ApiClient.apiKey["api_key"] = ""
+    ApiClient.apiKeyPrefix["api_key"] = ""
 
 ### HTTP request headers
 
- - **Content-Type**: Not defined
+ - **Content-Type**: application/json
  - **Accept**: Not defined
 
 <a id="createUsersWithArrayInput"></a>
 # **createUsersWithArrayInput**
-> createUsersWithArrayInput(body)
+> createUsersWithArrayInput(user)
 
 Creates list of users with given input array
 
+
+
 ### Example
 ```kotlin
 // Import classes:
@@ -72,9 +77,9 @@ Creates list of users with given input array
 //import org.openapitools.client.models.*
 
 val apiInstance = UserApi()
-val body : kotlin.collections.List<User> =  // kotlin.collections.List<User> | List of user object
+val user : kotlin.collections.List<User> =  // kotlin.collections.List<User> | List of user object
 try {
-    apiInstance.createUsersWithArrayInput(body)
+    apiInstance.createUsersWithArrayInput(user)
 } catch (e: ClientException) {
     println("4xx response calling UserApi#createUsersWithArrayInput")
     e.printStackTrace()
@@ -87,7 +92,7 @@ try {
 ### Parameters
 | Name | Type | Description  | Notes |
 | ------------- | ------------- | ------------- | ------------- |
-| **body** | [**kotlin.collections.List&lt;User&gt;**](User.md)| List of user object | |
+| **user** | [**kotlin.collections.List&lt;User&gt;**](User.md)| List of user object | |
 
 ### Return type
 
@@ -95,19 +100,24 @@ null (empty response body)
 
 ### Authorization
 
-No authorization required
+
+Configure api_key:
+    ApiClient.apiKey["api_key"] = ""
+    ApiClient.apiKeyPrefix["api_key"] = ""
 
 ### HTTP request headers
 
- - **Content-Type**: Not defined
+ - **Content-Type**: application/json
  - **Accept**: Not defined
 
 <a id="createUsersWithListInput"></a>
 # **createUsersWithListInput**
-> createUsersWithListInput(body)
+> createUsersWithListInput(user)
 
 Creates list of users with given input array
 
+
+
 ### Example
 ```kotlin
 // Import classes:
@@ -115,9 +125,9 @@ Creates list of users with given input array
 //import org.openapitools.client.models.*
 
 val apiInstance = UserApi()
-val body : kotlin.collections.List<User> =  // kotlin.collections.List<User> | List of user object
+val user : kotlin.collections.List<User> =  // kotlin.collections.List<User> | List of user object
 try {
-    apiInstance.createUsersWithListInput(body)
+    apiInstance.createUsersWithListInput(user)
 } catch (e: ClientException) {
     println("4xx response calling UserApi#createUsersWithListInput")
     e.printStackTrace()
@@ -130,7 +140,7 @@ try {
 ### Parameters
 | Name | Type | Description  | Notes |
 | ------------- | ------------- | ------------- | ------------- |
-| **body** | [**kotlin.collections.List&lt;User&gt;**](User.md)| List of user object | |
+| **user** | [**kotlin.collections.List&lt;User&gt;**](User.md)| List of user object | |
 
 ### Return type
 
@@ -138,11 +148,14 @@ null (empty response body)
 
 ### Authorization
 
-No authorization required
+
+Configure api_key:
+    ApiClient.apiKey["api_key"] = ""
+    ApiClient.apiKeyPrefix["api_key"] = ""
 
 ### HTTP request headers
 
- - **Content-Type**: Not defined
+ - **Content-Type**: application/json
  - **Accept**: Not defined
 
 <a id="deleteUser"></a>
@@ -183,7 +196,10 @@ null (empty response body)
 
 ### Authorization
 
-No authorization required
+
+Configure api_key:
+    ApiClient.apiKey["api_key"] = ""
+    ApiClient.apiKeyPrefix["api_key"] = ""
 
 ### HTTP request headers
 
@@ -196,6 +212,8 @@ No authorization required
 
 Get user by user name
 
+
+
 ### Example
 ```kotlin
 // Import classes:
@@ -240,6 +258,8 @@ No authorization required
 
 Logs user into the system
 
+
+
 ### Example
 ```kotlin
 // Import classes:
@@ -286,6 +306,8 @@ No authorization required
 
 Logs out current logged in user session
 
+
+
 ### Example
 ```kotlin
 // Import classes:
@@ -313,7 +335,10 @@ null (empty response body)
 
 ### Authorization
 
-No authorization required
+
+Configure api_key:
+    ApiClient.apiKey["api_key"] = ""
+    ApiClient.apiKeyPrefix["api_key"] = ""
 
 ### HTTP request headers
 
@@ -322,7 +347,7 @@ No authorization required
 
 <a id="updateUser"></a>
 # **updateUser**
-> updateUser(username, body)
+> updateUser(username, user)
 
 Updated user
 
@@ -336,9 +361,9 @@ This can only be done by the logged in user.
 
 val apiInstance = UserApi()
 val username : kotlin.String = username_example // kotlin.String | name that need to be deleted
-val body : User =  // User | Updated user object
+val user : User =  // User | Updated user object
 try {
-    apiInstance.updateUser(username, body)
+    apiInstance.updateUser(username, user)
 } catch (e: ClientException) {
     println("4xx response calling UserApi#updateUser")
     e.printStackTrace()
@@ -352,7 +377,7 @@ try {
 | **username** | **kotlin.String**| name that need to be deleted | |
 | Name | Type | Description  | Notes |
 | ------------- | ------------- | ------------- | ------------- |
-| **body** | [**User**](User.md)| Updated user object | |
+| **user** | [**User**](User.md)| Updated user object | |
 
 ### Return type
 
@@ -360,10 +385,13 @@ null (empty response body)
 
 ### Authorization
 
-No authorization required
+
+Configure api_key:
+    ApiClient.apiKey["api_key"] = ""
+    ApiClient.apiKeyPrefix["api_key"] = ""
 
 ### HTTP request headers
 
- - **Content-Type**: Not defined
+ - **Content-Type**: application/json
  - **Accept**: Not defined
 
diff --git a/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/apis/PetApi.kt b/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
index 71a98eb51647..d5605d2dfb6a 100644
--- a/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
+++ b/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/apis/PetApi.kt
@@ -50,20 +50,21 @@ open class PetApi(basePath: kotlin.String = defaultBasePath, client: Call.Factor
      * POST /pet
      * Add a new pet to the store
      * 
-     * @param body Pet object that needs to be added to the store
-     * @return void
+     * @param pet Pet object that needs to be added to the store
+     * @return Pet
      * @throws IllegalStateException If the request is not correctly configured
      * @throws IOException Rethrows the OkHttp execute method exception
      * @throws UnsupportedOperationException If the API returns an informational or redirection response
      * @throws ClientException If the API returns a client error response
      * @throws ServerException If the API returns a server error response
      */
+    @Suppress("UNCHECKED_CAST")
     @Throws(IllegalStateException::class, IOException::class, UnsupportedOperationException::class, ClientException::class, ServerException::class)
-    fun addPet(body: Pet) : Unit {
-        val localVarResponse = addPetWithHttpInfo(body = body)
+    fun addPet(pet: Pet) : Pet {
+        val localVarResponse = addPetWithHttpInfo(pet = pet)
 
         return when (localVarResponse.responseType) {
-            ResponseType.Success -> Unit
+            ResponseType.Success -> (localVarResponse as Success<*>).data as Pet
             ResponseType.Informational -> throw UnsupportedOperationException("Client does not support Informational responses.")
             ResponseType.Redirection -> throw UnsupportedOperationException("Client does not support Redirection responses.")
             ResponseType.ClientError -> {
@@ -81,16 +82,17 @@ open class PetApi(basePath: kotlin.String = defaultBasePath, client: Call.Factor
      * POST /pet
      * Add a new pet to the store
      * 
-     * @param body Pet object that needs to be added to the store
-     * @return ApiResponse<Unit?>
+     * @param pet Pet object that needs to be added to the store
+     * @return ApiResponse<Pet?>
      * @throws IllegalStateException If the request is not correctly configured
      * @throws IOException Rethrows the OkHttp execute method exception
      */
+    @Suppress("UNCHECKED_CAST")
     @Throws(IllegalStateException::class, IOException::class)
-    fun addPetWithHttpInfo(body: Pet) : ApiResponse<Unit?> {
-        val localVariableConfig = addPetRequestConfig(body = body)
+    fun addPetWithHttpInfo(pet: Pet) : ApiResponse<Pet?> {
+        val localVariableConfig = addPetRequestConfig(pet = pet)
 
-        return request<Pet, Unit>(
+        return request<Pet, Pet>(
             localVariableConfig
         )
     }
@@ -98,15 +100,16 @@ open class PetApi(basePath: kotlin.String = defaultBasePath, client: Call.Factor
     /**
      * To obtain the request config of the operation addPet
      *
-     * @param body Pet object that needs to be added to the store
+     * @param pet Pet object that needs to be added to the store
      * @return RequestConfig
      */
-    fun addPetRequestConfig(body: Pet) : RequestConfig<Pet> {
-        val localVariableBody = body
+    fun addPetRequestConfig(pet: Pet) : RequestConfig<Pet> {
+        val localVariableBody = pet
         val localVariableQuery: MultiValueMap = mutableMapOf()
         val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
         localVariableHeaders["Content-Type"] = "application/json"
-        
+        localVariableHeaders["Accept"] = "application/json"
+
         return RequestConfig(
             method = RequestMethod.POST,
             path = "/pet",
@@ -443,20 +446,21 @@ open class PetApi(basePath: kotlin.String = defaultBasePath, client: Call.Factor
      * PUT /pet
      * Update an existing pet
      * 
-     * @param body Pet object that needs to be added to the store
-     * @return void
+     * @param pet Pet object that needs to be added to the store
+     * @return Pet
      * @throws IllegalStateException If the request is not correctly configured
      * @throws IOException Rethrows the OkHttp execute method exception
      * @throws UnsupportedOperationException If the API returns an informational or redirection response
      * @throws ClientException If the API returns a client error response
      * @throws ServerException If the API returns a server error response
      */
+    @Suppress("UNCHECKED_CAST")
     @Throws(IllegalStateException::class, IOException::class, UnsupportedOperationException::class, ClientException::class, ServerException::class)
-    fun updatePet(body: Pet) : Unit {
-        val localVarResponse = updatePetWithHttpInfo(body = body)
+    fun updatePet(pet: Pet) : Pet {
+        val localVarResponse = updatePetWithHttpInfo(pet = pet)
 
         return when (localVarResponse.responseType) {
-            ResponseType.Success -> Unit
+            ResponseType.Success -> (localVarResponse as Success<*>).data as Pet
             ResponseType.Informational -> throw UnsupportedOperationException("Client does not support Informational responses.")
             ResponseType.Redirection -> throw UnsupportedOperationException("Client does not support Redirection responses.")
             ResponseType.ClientError -> {
@@ -474,16 +478,17 @@ open class PetApi(basePath: kotlin.String = defaultBasePath, client: Call.Factor
      * PUT /pet
      * Update an existing pet
      * 
-     * @param body Pet object that needs to be added to the store
-     * @return ApiResponse<Unit?>
+     * @param pet Pet object that needs to be added to the store
+     * @return ApiResponse<Pet?>
      * @throws IllegalStateException If the request is not correctly configured
      * @throws IOException Rethrows the OkHttp execute method exception
      */
+    @Suppress("UNCHECKED_CAST")
     @Throws(IllegalStateException::class, IOException::class)
-    fun updatePetWithHttpInfo(body: Pet) : ApiResponse<Unit?> {
-        val localVariableConfig = updatePetRequestConfig(body = body)
+    fun updatePetWithHttpInfo(pet: Pet) : ApiResponse<Pet?> {
+        val localVariableConfig = updatePetRequestConfig(pet = pet)
 
-        return request<Pet, Unit>(
+        return request<Pet, Pet>(
             localVariableConfig
         )
     }
@@ -491,15 +496,16 @@ open class PetApi(basePath: kotlin.String = defaultBasePath, client: Call.Factor
     /**
      * To obtain the request config of the operation updatePet
      *
-     * @param body Pet object that needs to be added to the store
+     * @param pet Pet object that needs to be added to the store
      * @return RequestConfig
      */
-    fun updatePetRequestConfig(body: Pet) : RequestConfig<Pet> {
-        val localVariableBody = body
+    fun updatePetRequestConfig(pet: Pet) : RequestConfig<Pet> {
+        val localVariableBody = pet
         val localVariableQuery: MultiValueMap = mutableMapOf()
         val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
         localVariableHeaders["Content-Type"] = "application/json"
-        
+        localVariableHeaders["Accept"] = "application/json"
+
         return RequestConfig(
             method = RequestMethod.PUT,
             path = "/pet",
diff --git a/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt b/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
index 4e1ab0677faf..83f36f7f7765 100644
--- a/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
+++ b/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/apis/StoreApi.kt
@@ -262,7 +262,7 @@ open class StoreApi(basePath: kotlin.String = defaultBasePath, client: Call.Fact
      * POST /store/order
      * Place an order for a pet
      * 
-     * @param body order placed for purchasing the pet
+     * @param order order placed for purchasing the pet
      * @return Order
      * @throws IllegalStateException If the request is not correctly configured
      * @throws IOException Rethrows the OkHttp execute method exception
@@ -272,8 +272,8 @@ open class StoreApi(basePath: kotlin.String = defaultBasePath, client: Call.Fact
      */
     @Suppress("UNCHECKED_CAST")
     @Throws(IllegalStateException::class, IOException::class, UnsupportedOperationException::class, ClientException::class, ServerException::class)
-    fun placeOrder(body: Order) : Order {
-        val localVarResponse = placeOrderWithHttpInfo(body = body)
+    fun placeOrder(order: Order) : Order {
+        val localVarResponse = placeOrderWithHttpInfo(order = order)
 
         return when (localVarResponse.responseType) {
             ResponseType.Success -> (localVarResponse as Success<*>).data as Order
@@ -294,15 +294,15 @@ open class StoreApi(basePath: kotlin.String = defaultBasePath, client: Call.Fact
      * POST /store/order
      * Place an order for a pet
      * 
-     * @param body order placed for purchasing the pet
+     * @param order order placed for purchasing the pet
      * @return ApiResponse<Order?>
      * @throws IllegalStateException If the request is not correctly configured
      * @throws IOException Rethrows the OkHttp execute method exception
      */
     @Suppress("UNCHECKED_CAST")
     @Throws(IllegalStateException::class, IOException::class)
-    fun placeOrderWithHttpInfo(body: Order) : ApiResponse<Order?> {
-        val localVariableConfig = placeOrderRequestConfig(body = body)
+    fun placeOrderWithHttpInfo(order: Order) : ApiResponse<Order?> {
+        val localVariableConfig = placeOrderRequestConfig(order = order)
 
         return request<Order, Order>(
             localVariableConfig
@@ -312,13 +312,14 @@ open class StoreApi(basePath: kotlin.String = defaultBasePath, client: Call.Fact
     /**
      * To obtain the request config of the operation placeOrder
      *
-     * @param body order placed for purchasing the pet
+     * @param order order placed for purchasing the pet
      * @return RequestConfig
      */
-    fun placeOrderRequestConfig(body: Order) : RequestConfig<Order> {
-        val localVariableBody = body
+    fun placeOrderRequestConfig(order: Order) : RequestConfig<Order> {
+        val localVariableBody = order
         val localVariableQuery: MultiValueMap = mutableMapOf()
         val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
+        localVariableHeaders["Content-Type"] = "application/json"
         localVariableHeaders["Accept"] = "application/json"
 
         return RequestConfig(
diff --git a/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/apis/UserApi.kt b/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
index 91bf8a6be5a3..59ae1b3fcd8d 100644
--- a/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
+++ b/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/apis/UserApi.kt
@@ -49,7 +49,7 @@ open class UserApi(basePath: kotlin.String = defaultBasePath, client: Call.Facto
      * POST /user
      * Create user
      * This can only be done by the logged in user.
-     * @param body Created user object
+     * @param user Created user object
      * @return void
      * @throws IllegalStateException If the request is not correctly configured
      * @throws IOException Rethrows the OkHttp execute method exception
@@ -58,8 +58,8 @@ open class UserApi(basePath: kotlin.String = defaultBasePath, client: Call.Facto
      * @throws ServerException If the API returns a server error response
      */
     @Throws(IllegalStateException::class, IOException::class, UnsupportedOperationException::class, ClientException::class, ServerException::class)
-    fun createUser(body: User) : Unit {
-        val localVarResponse = createUserWithHttpInfo(body = body)
+    fun createUser(user: User) : Unit {
+        val localVarResponse = createUserWithHttpInfo(user = user)
 
         return when (localVarResponse.responseType) {
             ResponseType.Success -> Unit
@@ -80,14 +80,14 @@ open class UserApi(basePath: kotlin.String = defaultBasePath, client: Call.Facto
      * POST /user
      * Create user
      * This can only be done by the logged in user.
-     * @param body Created user object
+     * @param user Created user object
      * @return ApiResponse<Unit?>
      * @throws IllegalStateException If the request is not correctly configured
      * @throws IOException Rethrows the OkHttp execute method exception
      */
     @Throws(IllegalStateException::class, IOException::class)
-    fun createUserWithHttpInfo(body: User) : ApiResponse<Unit?> {
-        val localVariableConfig = createUserRequestConfig(body = body)
+    fun createUserWithHttpInfo(user: User) : ApiResponse<Unit?> {
+        val localVariableConfig = createUserRequestConfig(user = user)
 
         return request<User, Unit>(
             localVariableConfig
@@ -97,20 +97,21 @@ open class UserApi(basePath: kotlin.String = defaultBasePath, client: Call.Facto
     /**
      * To obtain the request config of the operation createUser
      *
-     * @param body Created user object
+     * @param user Created user object
      * @return RequestConfig
      */
-    fun createUserRequestConfig(body: User) : RequestConfig<User> {
-        val localVariableBody = body
+    fun createUserRequestConfig(user: User) : RequestConfig<User> {
+        val localVariableBody = user
         val localVariableQuery: MultiValueMap = mutableMapOf()
         val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
+        localVariableHeaders["Content-Type"] = "application/json"
         
         return RequestConfig(
             method = RequestMethod.POST,
             path = "/user",
             query = localVariableQuery,
             headers = localVariableHeaders,
-            requiresAuthentication = false,
+            requiresAuthentication = true,
             body = localVariableBody
         )
     }
@@ -119,7 +120,7 @@ open class UserApi(basePath: kotlin.String = defaultBasePath, client: Call.Facto
      * POST /user/createWithArray
      * Creates list of users with given input array
      * 
-     * @param body List of user object
+     * @param user List of user object
      * @return void
      * @throws IllegalStateException If the request is not correctly configured
      * @throws IOException Rethrows the OkHttp execute method exception
@@ -128,8 +129,8 @@ open class UserApi(basePath: kotlin.String = defaultBasePath, client: Call.Facto
      * @throws ServerException If the API returns a server error response
      */
     @Throws(IllegalStateException::class, IOException::class, UnsupportedOperationException::class, ClientException::class, ServerException::class)
-    fun createUsersWithArrayInput(body: kotlin.collections.List<User>) : Unit {
-        val localVarResponse = createUsersWithArrayInputWithHttpInfo(body = body)
+    fun createUsersWithArrayInput(user: kotlin.collections.List<User>) : Unit {
+        val localVarResponse = createUsersWithArrayInputWithHttpInfo(user = user)
 
         return when (localVarResponse.responseType) {
             ResponseType.Success -> Unit
@@ -150,14 +151,14 @@ open class UserApi(basePath: kotlin.String = defaultBasePath, client: Call.Facto
      * POST /user/createWithArray
      * Creates list of users with given input array
      * 
-     * @param body List of user object
+     * @param user List of user object
      * @return ApiResponse<Unit?>
      * @throws IllegalStateException If the request is not correctly configured
      * @throws IOException Rethrows the OkHttp execute method exception
      */
     @Throws(IllegalStateException::class, IOException::class)
-    fun createUsersWithArrayInputWithHttpInfo(body: kotlin.collections.List<User>) : ApiResponse<Unit?> {
-        val localVariableConfig = createUsersWithArrayInputRequestConfig(body = body)
+    fun createUsersWithArrayInputWithHttpInfo(user: kotlin.collections.List<User>) : ApiResponse<Unit?> {
+        val localVariableConfig = createUsersWithArrayInputRequestConfig(user = user)
 
         return request<kotlin.collections.List<User>, Unit>(
             localVariableConfig
@@ -167,20 +168,21 @@ open class UserApi(basePath: kotlin.String = defaultBasePath, client: Call.Facto
     /**
      * To obtain the request config of the operation createUsersWithArrayInput
      *
-     * @param body List of user object
+     * @param user List of user object
      * @return RequestConfig
      */
-    fun createUsersWithArrayInputRequestConfig(body: kotlin.collections.List<User>) : RequestConfig<kotlin.collections.List<User>> {
-        val localVariableBody = body
+    fun createUsersWithArrayInputRequestConfig(user: kotlin.collections.List<User>) : RequestConfig<kotlin.collections.List<User>> {
+        val localVariableBody = user
         val localVariableQuery: MultiValueMap = mutableMapOf()
         val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
+        localVariableHeaders["Content-Type"] = "application/json"
         
         return RequestConfig(
             method = RequestMethod.POST,
             path = "/user/createWithArray",
             query = localVariableQuery,
             headers = localVariableHeaders,
-            requiresAuthentication = false,
+            requiresAuthentication = true,
             body = localVariableBody
         )
     }
@@ -189,7 +191,7 @@ open class UserApi(basePath: kotlin.String = defaultBasePath, client: Call.Facto
      * POST /user/createWithList
      * Creates list of users with given input array
      * 
-     * @param body List of user object
+     * @param user List of user object
      * @return void
      * @throws IllegalStateException If the request is not correctly configured
      * @throws IOException Rethrows the OkHttp execute method exception
@@ -198,8 +200,8 @@ open class UserApi(basePath: kotlin.String = defaultBasePath, client: Call.Facto
      * @throws ServerException If the API returns a server error response
      */
     @Throws(IllegalStateException::class, IOException::class, UnsupportedOperationException::class, ClientException::class, ServerException::class)
-    fun createUsersWithListInput(body: kotlin.collections.List<User>) : Unit {
-        val localVarResponse = createUsersWithListInputWithHttpInfo(body = body)
+    fun createUsersWithListInput(user: kotlin.collections.List<User>) : Unit {
+        val localVarResponse = createUsersWithListInputWithHttpInfo(user = user)
 
         return when (localVarResponse.responseType) {
             ResponseType.Success -> Unit
@@ -220,14 +222,14 @@ open class UserApi(basePath: kotlin.String = defaultBasePath, client: Call.Facto
      * POST /user/createWithList
      * Creates list of users with given input array
      * 
-     * @param body List of user object
+     * @param user List of user object
      * @return ApiResponse<Unit?>
      * @throws IllegalStateException If the request is not correctly configured
      * @throws IOException Rethrows the OkHttp execute method exception
      */
     @Throws(IllegalStateException::class, IOException::class)
-    fun createUsersWithListInputWithHttpInfo(body: kotlin.collections.List<User>) : ApiResponse<Unit?> {
-        val localVariableConfig = createUsersWithListInputRequestConfig(body = body)
+    fun createUsersWithListInputWithHttpInfo(user: kotlin.collections.List<User>) : ApiResponse<Unit?> {
+        val localVariableConfig = createUsersWithListInputRequestConfig(user = user)
 
         return request<kotlin.collections.List<User>, Unit>(
             localVariableConfig
@@ -237,20 +239,21 @@ open class UserApi(basePath: kotlin.String = defaultBasePath, client: Call.Facto
     /**
      * To obtain the request config of the operation createUsersWithListInput
      *
-     * @param body List of user object
+     * @param user List of user object
      * @return RequestConfig
      */
-    fun createUsersWithListInputRequestConfig(body: kotlin.collections.List<User>) : RequestConfig<kotlin.collections.List<User>> {
-        val localVariableBody = body
+    fun createUsersWithListInputRequestConfig(user: kotlin.collections.List<User>) : RequestConfig<kotlin.collections.List<User>> {
+        val localVariableBody = user
         val localVariableQuery: MultiValueMap = mutableMapOf()
         val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
+        localVariableHeaders["Content-Type"] = "application/json"
         
         return RequestConfig(
             method = RequestMethod.POST,
             path = "/user/createWithList",
             query = localVariableQuery,
             headers = localVariableHeaders,
-            requiresAuthentication = false,
+            requiresAuthentication = true,
             body = localVariableBody
         )
     }
@@ -320,7 +323,7 @@ open class UserApi(basePath: kotlin.String = defaultBasePath, client: Call.Facto
             path = "/user/{username}".replace("{"+"username"+"}", encodeURIComponent(username.toString())),
             query = localVariableQuery,
             headers = localVariableHeaders,
-            requiresAuthentication = false,
+            requiresAuthentication = true,
             body = localVariableBody
         )
     }
@@ -540,7 +543,7 @@ open class UserApi(basePath: kotlin.String = defaultBasePath, client: Call.Facto
             path = "/user/logout",
             query = localVariableQuery,
             headers = localVariableHeaders,
-            requiresAuthentication = false,
+            requiresAuthentication = true,
             body = localVariableBody
         )
     }
@@ -550,7 +553,7 @@ open class UserApi(basePath: kotlin.String = defaultBasePath, client: Call.Facto
      * Updated user
      * This can only be done by the logged in user.
      * @param username name that need to be deleted
-     * @param body Updated user object
+     * @param user Updated user object
      * @return void
      * @throws IllegalStateException If the request is not correctly configured
      * @throws IOException Rethrows the OkHttp execute method exception
@@ -559,8 +562,8 @@ open class UserApi(basePath: kotlin.String = defaultBasePath, client: Call.Facto
      * @throws ServerException If the API returns a server error response
      */
     @Throws(IllegalStateException::class, IOException::class, UnsupportedOperationException::class, ClientException::class, ServerException::class)
-    fun updateUser(username: kotlin.String, body: User) : Unit {
-        val localVarResponse = updateUserWithHttpInfo(username = username, body = body)
+    fun updateUser(username: kotlin.String, user: User) : Unit {
+        val localVarResponse = updateUserWithHttpInfo(username = username, user = user)
 
         return when (localVarResponse.responseType) {
             ResponseType.Success -> Unit
@@ -582,14 +585,14 @@ open class UserApi(basePath: kotlin.String = defaultBasePath, client: Call.Facto
      * Updated user
      * This can only be done by the logged in user.
      * @param username name that need to be deleted
-     * @param body Updated user object
+     * @param user Updated user object
      * @return ApiResponse<Unit?>
      * @throws IllegalStateException If the request is not correctly configured
      * @throws IOException Rethrows the OkHttp execute method exception
      */
     @Throws(IllegalStateException::class, IOException::class)
-    fun updateUserWithHttpInfo(username: kotlin.String, body: User) : ApiResponse<Unit?> {
-        val localVariableConfig = updateUserRequestConfig(username = username, body = body)
+    fun updateUserWithHttpInfo(username: kotlin.String, user: User) : ApiResponse<Unit?> {
+        val localVariableConfig = updateUserRequestConfig(username = username, user = user)
 
         return request<User, Unit>(
             localVariableConfig
@@ -600,20 +603,21 @@ open class UserApi(basePath: kotlin.String = defaultBasePath, client: Call.Facto
      * To obtain the request config of the operation updateUser
      *
      * @param username name that need to be deleted
-     * @param body Updated user object
+     * @param user Updated user object
      * @return RequestConfig
      */
-    fun updateUserRequestConfig(username: kotlin.String, body: User) : RequestConfig<User> {
-        val localVariableBody = body
+    fun updateUserRequestConfig(username: kotlin.String, user: User) : RequestConfig<User> {
+        val localVariableBody = user
         val localVariableQuery: MultiValueMap = mutableMapOf()
         val localVariableHeaders: MutableMap<String, String> = mutableMapOf()
+        localVariableHeaders["Content-Type"] = "application/json"
         
         return RequestConfig(
             method = RequestMethod.PUT,
             path = "/user/{username}".replace("{"+"username"+"}", encodeURIComponent(username.toString())),
             query = localVariableQuery,
             headers = localVariableHeaders,
-            requiresAuthentication = false,
+            requiresAuthentication = true,
             body = localVariableBody
         )
     }
diff --git a/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/Category.kt b/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/Category.kt
index 87eacb1365a5..92998b83400d 100644
--- a/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/Category.kt
+++ b/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/Category.kt
@@ -35,6 +35,7 @@ data class Category (
     val name: kotlin.String? = null
 
 ) {
+    companion object { }
 
 
 }
diff --git a/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/ModelApiResponse.kt b/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/ModelApiResponse.kt
index fe2d51d4ef04..add1de46e967 100644
--- a/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/ModelApiResponse.kt
+++ b/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/ModelApiResponse.kt
@@ -39,6 +39,7 @@ data class ModelApiResponse (
     val message: kotlin.String? = null
 
 ) {
+    companion object { }
 
 
 }
diff --git a/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/Order.kt b/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/Order.kt
index b9f182f53b53..c08af4d76416 100644
--- a/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/Order.kt
+++ b/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/Order.kt
@@ -52,6 +52,7 @@ data class Order (
     val complete: kotlin.Boolean? = false
 
 ) {
+    companion object { }
 
     /**
      * Order Status
diff --git a/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/Pet.kt b/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/Pet.kt
index 57c97dd3d089..6fc1fbf59b2b 100644
--- a/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/Pet.kt
+++ b/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/Pet.kt
@@ -51,9 +51,11 @@ data class Pet (
 
     /* pet status in the store */
     @SerializedName("status")
+    @Deprecated(message = "This property is deprecated.")
     val status: Pet.Status? = null
 
 ) {
+    companion object { }
 
     /**
      * pet status in the store
diff --git a/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/Tag.kt b/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/Tag.kt
index f66db9ea55e8..eb8bf964dc50 100644
--- a/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/Tag.kt
+++ b/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/Tag.kt
@@ -35,6 +35,7 @@ data class Tag (
     val name: kotlin.String? = null
 
 ) {
+    companion object { }
 
 
 }
diff --git a/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/User.kt b/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/User.kt
index 62b3ce81f9bf..e2c260392392 100644
--- a/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/User.kt
+++ b/samples/client/petstore/kotlin-gson/src/main/kotlin/org/openapitools/client/models/User.kt
@@ -60,6 +60,7 @@ data class User (
     val userStatus: kotlin.Int? = null
 
 ) {
+    companion object { }
 
 
 }