diff --git a/datamodel/openapi/openapi-api-apache-sample/src/main/java/com/sap/cloud/sdk/datamodel/openapi/apache/petstore/api/DefaultApi.java b/datamodel/openapi/openapi-api-apache-sample/src/main/java/com/sap/cloud/sdk/datamodel/openapi/apache/petstore/api/DefaultApi.java
index 1e5c00ff0..3113c55c8 100644
--- a/datamodel/openapi/openapi-api-apache-sample/src/main/java/com/sap/cloud/sdk/datamodel/openapi/apache/petstore/api/DefaultApi.java
+++ b/datamodel/openapi/openapi-api-apache-sample/src/main/java/com/sap/cloud/sdk/datamodel/openapi/apache/petstore/api/DefaultApi.java
@@ -53,6 +53,21 @@ public DefaultApi( @Nonnull final ApiClient apiClient )
         super(apiClient);
     }
 
+    /**
+     * Creates a new API instance with additional default headers.
+     *
+     * @param defaultHeaders
+     *            Additional headers to include in all requests
+     * @return A new API instance with the combined headers
+     */
+    public DefaultApi withDefaultHeaders( @Nonnull final Map<String, String> defaultHeaders )
+    {
+        final var api = new DefaultApi(apiClient);
+        api.defaultHeaders.putAll(this.defaultHeaders);
+        api.defaultHeaders.putAll(defaultHeaders);
+        return api;
+    }
+
     /**
      * <p>
      * <p>
@@ -85,7 +100,7 @@ public Pet addPet( @Nonnull final PetInput pet )
         final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
         final List<Pair> localVarQueryParams = new ArrayList<Pair>();
         final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-        final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+        final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
         final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
 
         final String[] localVarAccepts = { "application/json" };
@@ -145,7 +160,7 @@ public OpenApiResponse deletePet( @Nonnull final Long id )
         final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
         final List<Pair> localVarQueryParams = new ArrayList<Pair>();
         final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-        final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+        final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
         final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
 
         final String[] localVarAccepts = { "application/json" };
@@ -207,7 +222,7 @@ public Pet findPetById( @Nonnull final Long id )
         final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
         final List<Pair> localVarQueryParams = new ArrayList<Pair>();
         final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-        final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+        final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
         final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
 
         final String[] localVarAccepts = { "application/json", "application/xml", "text/xml", "text/html" };
@@ -264,7 +279,7 @@ public List<Pet> findPets( @Nullable final List<String> tags, @Nullable final In
         final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
         final List<Pair> localVarQueryParams = new ArrayList<Pair>();
         final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-        final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+        final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
         final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
 
         localVarCollectionQueryParams.addAll(ApiClient.parameterToPairs("csv", "tags", tags));
diff --git a/datamodel/openapi/openapi-api-apache-sample/src/main/java/com/sap/cloud/sdk/datamodel/openapi/apache/sodastore/api/OrdersApi.java b/datamodel/openapi/openapi-api-apache-sample/src/main/java/com/sap/cloud/sdk/datamodel/openapi/apache/sodastore/api/OrdersApi.java
index a0b7df0b4..c95cca621 100644
--- a/datamodel/openapi/openapi-api-apache-sample/src/main/java/com/sap/cloud/sdk/datamodel/openapi/apache/sodastore/api/OrdersApi.java
+++ b/datamodel/openapi/openapi-api-apache-sample/src/main/java/com/sap/cloud/sdk/datamodel/openapi/apache/sodastore/api/OrdersApi.java
@@ -50,6 +50,21 @@ public OrdersApi( @Nonnull final ApiClient apiClient )
         super(apiClient);
     }
 
+    /**
+     * Creates a new API instance with additional default headers.
+     *
+     * @param defaultHeaders
+     *            Additional headers to include in all requests
+     * @return A new API instance with the combined headers
+     */
+    public OrdersApi withDefaultHeaders( @Nonnull final Map<String, String> defaultHeaders )
+    {
+        final var api = new OrdersApi(apiClient);
+        api.defaultHeaders.putAll(this.defaultHeaders);
+        api.defaultHeaders.putAll(defaultHeaders);
+        return api;
+    }
+
     /**
      * <p>
      * Create a new order
@@ -80,7 +95,7 @@ public Order ordersPost( @Nonnull final Order order )
         final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
         final List<Pair> localVarQueryParams = new ArrayList<Pair>();
         final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-        final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+        final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
         final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
 
         final String[] localVarAccepts = { "application/json" };
diff --git a/datamodel/openapi/openapi-api-apache-sample/src/main/java/com/sap/cloud/sdk/datamodel/openapi/apache/sodastore/api/SodasApi.java b/datamodel/openapi/openapi-api-apache-sample/src/main/java/com/sap/cloud/sdk/datamodel/openapi/apache/sodastore/api/SodasApi.java
index 94272d5d6..bdcadeb55 100644
--- a/datamodel/openapi/openapi-api-apache-sample/src/main/java/com/sap/cloud/sdk/datamodel/openapi/apache/sodastore/api/SodasApi.java
+++ b/datamodel/openapi/openapi-api-apache-sample/src/main/java/com/sap/cloud/sdk/datamodel/openapi/apache/sodastore/api/SodasApi.java
@@ -52,6 +52,21 @@ public SodasApi( @Nonnull final ApiClient apiClient )
         super(apiClient);
     }
 
+    /**
+     * Creates a new API instance with additional default headers.
+     *
+     * @param defaultHeaders
+     *            Additional headers to include in all requests
+     * @return A new API instance with the combined headers
+     */
+    public SodasApi withDefaultHeaders( @Nonnull final Map<String, String> defaultHeaders )
+    {
+        final var api = new SodasApi(apiClient);
+        api.defaultHeaders.putAll(this.defaultHeaders);
+        api.defaultHeaders.putAll(defaultHeaders);
+        return api;
+    }
+
     /**
      * <p>
      * Download soda product data as binary
@@ -86,7 +101,7 @@ public byte[] sodasDownloadIdGet( @Nonnull final Long id )
         final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
         final List<Pair> localVarQueryParams = new ArrayList<Pair>();
         final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-        final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+        final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
         final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
 
         final String[] localVarAccepts = { "application/octet-stream" };
@@ -137,7 +152,7 @@ public List<SodaWithId> sodasGet()
         final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
         final List<Pair> localVarQueryParams = new ArrayList<Pair>();
         final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-        final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+        final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
         final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
 
         final String[] localVarAccepts = { "application/json" };
@@ -199,7 +214,7 @@ public SodaWithId sodasIdGet( @Nonnull final Long id )
         final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
         final List<Pair> localVarQueryParams = new ArrayList<Pair>();
         final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-        final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+        final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
         final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
 
         final String[] localVarAccepts = { "application/json" };
@@ -262,7 +277,7 @@ public Soda sodasPut( @Nonnull final SodaWithId sodaWithId )
         final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
         final List<Pair> localVarQueryParams = new ArrayList<Pair>();
         final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-        final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+        final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
         final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
 
         final String[] localVarAccepts = { "application/json" };
diff --git a/datamodel/openapi/openapi-core-apache/src/main/java/com/sap/cloud/sdk/services/openapi/apache/apiclient/BaseApi.java b/datamodel/openapi/openapi-core-apache/src/main/java/com/sap/cloud/sdk/services/openapi/apache/apiclient/BaseApi.java
index d9bdec66a..24af72aa9 100644
--- a/datamodel/openapi/openapi-core-apache/src/main/java/com/sap/cloud/sdk/services/openapi/apache/apiclient/BaseApi.java
+++ b/datamodel/openapi/openapi-core-apache/src/main/java/com/sap/cloud/sdk/services/openapi/apache/apiclient/BaseApi.java
@@ -12,6 +12,9 @@
 
 package com.sap.cloud.sdk.services.openapi.apache.apiclient;
 
+import java.util.HashMap;
+import java.util.Map;
+
 import javax.annotation.Nonnull;
 
 import com.sap.cloud.sdk.cloudplatform.connectivity.Destination;
@@ -26,6 +29,11 @@ public abstract class BaseApi
      */
     protected final ApiClient apiClient;
 
+    /**
+     * Default headers to be included in every request.
+     */
+    protected final Map<String, String> defaultHeaders = new HashMap<>();
+
     /**
      * Creates a new BaseApi instance with default configuration.
      */
diff --git a/datamodel/openapi/openapi-generator/src/main/resources/openapi-generator/mustache-templates/libraries/apache-httpclient/api.mustache b/datamodel/openapi/openapi-generator/src/main/resources/openapi-generator/mustache-templates/libraries/apache-httpclient/api.mustache
index d1c442437..b8d3f2b97 100644
--- a/datamodel/openapi/openapi-generator/src/main/resources/openapi-generator/mustache-templates/libraries/apache-httpclient/api.mustache
+++ b/datamodel/openapi/openapi-generator/src/main/resources/openapi-generator/mustache-templates/libraries/apache-httpclient/api.mustache
@@ -91,8 +91,25 @@ public class {{classname}} extends BaseApi {
     {
     super(aiCoreService.getApiClient());
     }
+
+    private {{classname}}(@Nonnull final ApiClient apiClient) {
+        super(apiClient);
+    }
     {{/aiSdkConstructor}}
 
+    /**
+    * Creates a new API instance with additional default headers.
+    *
+    * @param defaultHeaders Additional headers to include in all requests
+    * @return A new API instance with the combined headers
+    */
+    public {{classname}} withDefaultHeaders(@Nonnull final Map<String, String> defaultHeaders) {
+        final var api = new {{classname}}(apiClient);
+        api.defaultHeaders.putAll(this.defaultHeaders);
+        api.defaultHeaders.putAll(defaultHeaders);
+        return api;
+    }
+
     {{#operation}}
         {{#hasOptionalParams}}
             /**
diff --git a/datamodel/openapi/openapi-generator/src/main/resources/openapi-generator/mustache-templates/libraries/apache-httpclient/operationBody.mustache b/datamodel/openapi/openapi-generator/src/main/resources/openapi-generator/mustache-templates/libraries/apache-httpclient/operationBody.mustache
index dd83ac4c9..7bd842f55 100644
--- a/datamodel/openapi/openapi-generator/src/main/resources/openapi-generator/mustache-templates/libraries/apache-httpclient/operationBody.mustache
+++ b/datamodel/openapi/openapi-generator/src/main/resources/openapi-generator/mustache-templates/libraries/apache-httpclient/operationBody.mustache
@@ -12,7 +12,7 @@ final String localVarPath = "{{{path}}}"{{#pathParams}}
 final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
 final List<Pair> localVarQueryParams = new ArrayList<Pair>();
 final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
 final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
 
 {{#queryParams}}
diff --git a/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-for-ai-sdk/output/com/sap/cloud/sdk/services/builder/api/AwesomeSodaApi.java b/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-for-ai-sdk/output/com/sap/cloud/sdk/services/builder/api/AwesomeSodaApi.java
index 2feef4ee1..9af6be1d5 100644
--- a/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-for-ai-sdk/output/com/sap/cloud/sdk/services/builder/api/AwesomeSodaApi.java
+++ b/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-for-ai-sdk/output/com/sap/cloud/sdk/services/builder/api/AwesomeSodaApi.java
@@ -55,6 +55,23 @@ public AwesomeSodaApi( @Nonnull final AiCoreService aiCoreService )
     super(aiCoreService.getApiClient());
     }
 
+    private AwesomeSodaApi(@Nonnull final ApiClient apiClient) {
+        super(apiClient);
+    }
+
+    /**
+    * Creates a new API instance with additional default headers.
+    *
+    * @param defaultHeaders Additional headers to include in all requests
+    * @return A new API instance with the combined headers
+    */
+    public AwesomeSodaApi withDefaultHeaders(@Nonnull final Map<String, String> defaultHeaders) {
+        final var api = new AwesomeSodaApi(apiClient);
+        api.defaultHeaders.putAll(this.defaultHeaders);
+        api.defaultHeaders.putAll(defaultHeaders);
+        return api;
+    }
+
 
         /**
          * <p>Add a new soda to the store
@@ -80,7 +97,7 @@ public Soda addSoda(@Nonnull final NewSoda newSoda) throws OpenApiRequestExcepti
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
             
                                     
diff --git a/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-for-ai-sdk/output/com/sap/cloud/sdk/services/builder/api/AwesomeSodasApi.java b/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-for-ai-sdk/output/com/sap/cloud/sdk/services/builder/api/AwesomeSodasApi.java
index 5f33c5144..612b8ed8e 100644
--- a/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-for-ai-sdk/output/com/sap/cloud/sdk/services/builder/api/AwesomeSodasApi.java
+++ b/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-for-ai-sdk/output/com/sap/cloud/sdk/services/builder/api/AwesomeSodasApi.java
@@ -54,6 +54,23 @@ public AwesomeSodasApi( @Nonnull final AiCoreService aiCoreService )
     super(aiCoreService.getApiClient());
     }
 
+    private AwesomeSodasApi(@Nonnull final ApiClient apiClient) {
+        super(apiClient);
+    }
+
+    /**
+    * Creates a new API instance with additional default headers.
+    *
+    * @param defaultHeaders Additional headers to include in all requests
+    * @return A new API instance with the combined headers
+    */
+    public AwesomeSodasApi withDefaultHeaders(@Nonnull final Map<String, String> defaultHeaders) {
+        final var api = new AwesomeSodasApi(apiClient);
+        api.defaultHeaders.putAll(this.defaultHeaders);
+        api.defaultHeaders.putAll(defaultHeaders);
+        return api;
+    }
+
 
         /**
          * <p>Get a list of all sodas
@@ -71,7 +88,7 @@ public List<Soda> getSodas() throws OpenApiRequestException {
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
             
                                     
diff --git a/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-for-ai-sdk/output/com/sap/cloud/sdk/services/builder/api/DefaultApi.java b/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-for-ai-sdk/output/com/sap/cloud/sdk/services/builder/api/DefaultApi.java
index b47b94f4c..009f1bd08 100644
--- a/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-for-ai-sdk/output/com/sap/cloud/sdk/services/builder/api/DefaultApi.java
+++ b/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-for-ai-sdk/output/com/sap/cloud/sdk/services/builder/api/DefaultApi.java
@@ -55,6 +55,23 @@ public DefaultApi( @Nonnull final AiCoreService aiCoreService )
     super(aiCoreService.getApiClient());
     }
 
+    private DefaultApi(@Nonnull final ApiClient apiClient) {
+        super(apiClient);
+    }
+
+    /**
+    * Creates a new API instance with additional default headers.
+    *
+    * @param defaultHeaders Additional headers to include in all requests
+    * @return A new API instance with the combined headers
+    */
+    public DefaultApi withDefaultHeaders(@Nonnull final Map<String, String> defaultHeaders) {
+        final var api = new DefaultApi(apiClient);
+        api.defaultHeaders.putAll(this.defaultHeaders);
+        api.defaultHeaders.putAll(defaultHeaders);
+        return api;
+    }
+
 
         /**
          * <p>Delete a specific soda from the store
@@ -82,7 +99,7 @@ public OpenApiResponse deleteSodaById(@Nonnull final Long sodaId) throws OpenApi
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
             
                                     
@@ -138,7 +155,7 @@ public Soda getSodaById(@Nonnull final Long sodaId) throws OpenApiRequestExcepti
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
             
                                     
@@ -202,7 +219,7 @@ public Soda updateSodaById(@Nonnull final Long sodaId, @Nonnull final UpdateSoda
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
             
                                     
diff --git a/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-vendor-extension-json/output/com/sap/cloud/sdk/services/apiclassvendorextension/api/AwesomeSodaApi.java b/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-vendor-extension-json/output/com/sap/cloud/sdk/services/apiclassvendorextension/api/AwesomeSodaApi.java
index 639a7a5f8..3caa324a1 100644
--- a/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-vendor-extension-json/output/com/sap/cloud/sdk/services/apiclassvendorextension/api/AwesomeSodaApi.java
+++ b/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-vendor-extension-json/output/com/sap/cloud/sdk/services/apiclassvendorextension/api/AwesomeSodaApi.java
@@ -57,6 +57,19 @@ public AwesomeSodaApi(@Nonnull final ApiClient apiClient) {
     super(apiClient);
     }
 
+    /**
+    * Creates a new API instance with additional default headers.
+    *
+    * @param defaultHeaders Additional headers to include in all requests
+    * @return A new API instance with the combined headers
+    */
+    public AwesomeSodaApi withDefaultHeaders(@Nonnull final Map<String, String> defaultHeaders) {
+        final var api = new AwesomeSodaApi(apiClient);
+        api.defaultHeaders.putAll(this.defaultHeaders);
+        api.defaultHeaders.putAll(defaultHeaders);
+        return api;
+    }
+
 
         /**
          * <p>Add a new soda to the store
@@ -82,7 +95,7 @@ public Soda addSoda(@Nonnull final NewSoda newSoda) throws OpenApiRequestExcepti
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
             
                                     
diff --git a/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-vendor-extension-json/output/com/sap/cloud/sdk/services/apiclassvendorextension/api/AwesomeSodasApi.java b/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-vendor-extension-json/output/com/sap/cloud/sdk/services/apiclassvendorextension/api/AwesomeSodasApi.java
index 2db36f4d7..11aa991c4 100644
--- a/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-vendor-extension-json/output/com/sap/cloud/sdk/services/apiclassvendorextension/api/AwesomeSodasApi.java
+++ b/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-vendor-extension-json/output/com/sap/cloud/sdk/services/apiclassvendorextension/api/AwesomeSodasApi.java
@@ -56,6 +56,19 @@ public AwesomeSodasApi(@Nonnull final ApiClient apiClient) {
     super(apiClient);
     }
 
+    /**
+    * Creates a new API instance with additional default headers.
+    *
+    * @param defaultHeaders Additional headers to include in all requests
+    * @return A new API instance with the combined headers
+    */
+    public AwesomeSodasApi withDefaultHeaders(@Nonnull final Map<String, String> defaultHeaders) {
+        final var api = new AwesomeSodasApi(apiClient);
+        api.defaultHeaders.putAll(this.defaultHeaders);
+        api.defaultHeaders.putAll(defaultHeaders);
+        return api;
+    }
+
 
         /**
          * <p>Get a list of all sodas
@@ -73,7 +86,7 @@ public List<Soda> getSodas() throws OpenApiRequestException {
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
             
                                     
diff --git a/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-vendor-extension-json/output/com/sap/cloud/sdk/services/apiclassvendorextension/api/DefaultApi.java b/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-vendor-extension-json/output/com/sap/cloud/sdk/services/apiclassvendorextension/api/DefaultApi.java
index 14c82e950..4888f239b 100644
--- a/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-vendor-extension-json/output/com/sap/cloud/sdk/services/apiclassvendorextension/api/DefaultApi.java
+++ b/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-vendor-extension-json/output/com/sap/cloud/sdk/services/apiclassvendorextension/api/DefaultApi.java
@@ -57,6 +57,19 @@ public DefaultApi(@Nonnull final ApiClient apiClient) {
     super(apiClient);
     }
 
+    /**
+    * Creates a new API instance with additional default headers.
+    *
+    * @param defaultHeaders Additional headers to include in all requests
+    * @return A new API instance with the combined headers
+    */
+    public DefaultApi withDefaultHeaders(@Nonnull final Map<String, String> defaultHeaders) {
+        final var api = new DefaultApi(apiClient);
+        api.defaultHeaders.putAll(this.defaultHeaders);
+        api.defaultHeaders.putAll(defaultHeaders);
+        return api;
+    }
+
 
         /**
          * <p>Delete a specific soda from the store
@@ -84,7 +97,7 @@ public OpenApiResponse deleteSodaById(@Nonnull final Long sodaId) throws OpenApi
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
             
                                     
@@ -140,7 +153,7 @@ public Soda getSodaById(@Nonnull final Long sodaId) throws OpenApiRequestExcepti
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
             
                                     
@@ -204,7 +217,7 @@ public Soda updateSodaById(@Nonnull final Long sodaId, @Nonnull final UpdateSoda
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
             
                                     
diff --git a/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-vendor-extension-yaml/output/com/sap/cloud/sdk/services/apiclassvendorextension/api/DefaultApi.java b/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-vendor-extension-yaml/output/com/sap/cloud/sdk/services/apiclassvendorextension/api/DefaultApi.java
index ff1a6201a..4a7d910ed 100644
--- a/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-vendor-extension-yaml/output/com/sap/cloud/sdk/services/apiclassvendorextension/api/DefaultApi.java
+++ b/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/api-class-vendor-extension-yaml/output/com/sap/cloud/sdk/services/apiclassvendorextension/api/DefaultApi.java
@@ -58,6 +58,19 @@ public DefaultApi(@Nonnull final ApiClient apiClient) {
     super(apiClient);
     }
 
+    /**
+    * Creates a new API instance with additional default headers.
+    *
+    * @param defaultHeaders Additional headers to include in all requests
+    * @return A new API instance with the combined headers
+    */
+    public DefaultApi withDefaultHeaders(@Nonnull final Map<String, String> defaultHeaders) {
+        final var api = new DefaultApi(apiClient);
+        api.defaultHeaders.putAll(this.defaultHeaders);
+        api.defaultHeaders.putAll(defaultHeaders);
+        return api;
+    }
+
 
         /**
          * <p>Add a new soda to the store
@@ -83,7 +96,7 @@ public Soda addSoda(@Nonnull final NewSoda newSoda) throws OpenApiRequestExcepti
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
             
                                     
@@ -139,7 +152,7 @@ public OpenApiResponse deleteSodaById(@Nonnull final Long sodaId) throws OpenApi
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
             
                                     
@@ -195,7 +208,7 @@ public Soda getSodaById(@Nonnull final Long sodaId) throws OpenApiRequestExcepti
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
             
                                     
@@ -241,7 +254,7 @@ public List<Soda> getSodas() throws OpenApiRequestException {
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
             
                                     
@@ -305,7 +318,7 @@ public Soda updateSodaById(@Nonnull final Long sodaId, @Nonnull final UpdateSoda
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
             
                                     
diff --git a/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/inlineobject-schemas-enabled/output/com/sap/cloud/sdk/services/inlineobject/api/DefaultApi.java b/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/inlineobject-schemas-enabled/output/com/sap/cloud/sdk/services/inlineobject/api/DefaultApi.java
index 3cf20579e..eda6a2aac 100644
--- a/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/inlineobject-schemas-enabled/output/com/sap/cloud/sdk/services/inlineobject/api/DefaultApi.java
+++ b/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/inlineobject-schemas-enabled/output/com/sap/cloud/sdk/services/inlineobject/api/DefaultApi.java
@@ -59,6 +59,19 @@ public DefaultApi(@Nonnull final ApiClient apiClient) {
     super(apiClient);
     }
 
+    /**
+    * Creates a new API instance with additional default headers.
+    *
+    * @param defaultHeaders Additional headers to include in all requests
+    * @return A new API instance with the combined headers
+    */
+    public DefaultApi withDefaultHeaders(@Nonnull final Map<String, String> defaultHeaders) {
+        final var api = new DefaultApi(apiClient);
+        api.defaultHeaders.putAll(this.defaultHeaders);
+        api.defaultHeaders.putAll(defaultHeaders);
+        return api;
+    }
+
 
         /**
          * <p>Get details of a specific soda
@@ -87,7 +100,7 @@ public Soda getSodaById(@Nonnull final Long sodaId) throws OpenApiRequestExcepti
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
             
                                     
diff --git a/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/partial-generation/output/com/sap/cloud/sdk/services/builder/api/DefaultApi.java b/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/partial-generation/output/com/sap/cloud/sdk/services/builder/api/DefaultApi.java
index 554cef3e0..0e5a58f2e 100644
--- a/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/partial-generation/output/com/sap/cloud/sdk/services/builder/api/DefaultApi.java
+++ b/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/partial-generation/output/com/sap/cloud/sdk/services/builder/api/DefaultApi.java
@@ -58,6 +58,19 @@ public DefaultApi(@Nonnull final ApiClient apiClient) {
     super(apiClient);
     }
 
+    /**
+    * Creates a new API instance with additional default headers.
+    *
+    * @param defaultHeaders Additional headers to include in all requests
+    * @return A new API instance with the combined headers
+    */
+    public DefaultApi withDefaultHeaders(@Nonnull final Map<String, String> defaultHeaders) {
+        final var api = new DefaultApi(apiClient);
+        api.defaultHeaders.putAll(this.defaultHeaders);
+        api.defaultHeaders.putAll(defaultHeaders);
+        return api;
+    }
+
 
         /**
          * <p>Delete a specific soda from the store
@@ -85,7 +98,7 @@ public OpenApiResponse deleteSodaById(@Nonnull final Long sodaId) throws OpenApi
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
             
                                     
@@ -141,7 +154,7 @@ public SodaWithFoo getSodaById(@Nonnull final Long sodaId) throws OpenApiRequest
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
             
                                     
@@ -205,7 +218,7 @@ public Soda updateSodaById(@Nonnull final Long sodaId, @Nonnull final UpdateSoda
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
             
                                     
diff --git a/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/remove-operation-id-prefix/output/com/sap/cloud/sdk/services/builder/api/OrdersApi.java b/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/remove-operation-id-prefix/output/com/sap/cloud/sdk/services/builder/api/OrdersApi.java
index 2f94d3813..eb1b5513e 100644
--- a/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/remove-operation-id-prefix/output/com/sap/cloud/sdk/services/builder/api/OrdersApi.java
+++ b/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/remove-operation-id-prefix/output/com/sap/cloud/sdk/services/builder/api/OrdersApi.java
@@ -56,6 +56,19 @@ public OrdersApi(@Nonnull final ApiClient apiClient) {
     super(apiClient);
     }
 
+    /**
+    * Creates a new API instance with additional default headers.
+    *
+    * @param defaultHeaders Additional headers to include in all requests
+    * @return A new API instance with the combined headers
+    */
+    public OrdersApi withDefaultHeaders(@Nonnull final Map<String, String> defaultHeaders) {
+        final var api = new OrdersApi(apiClient);
+        api.defaultHeaders.putAll(this.defaultHeaders);
+        api.defaultHeaders.putAll(defaultHeaders);
+        return api;
+    }
+
 
         /**
          * <p>Create a new order
@@ -81,7 +94,7 @@ public Order get(@Nonnull final Order order) throws OpenApiRequestException {
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
             
                                     
diff --git a/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/remove-operation-id-prefix/output/com/sap/cloud/sdk/services/builder/api/SodasApi.java b/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/remove-operation-id-prefix/output/com/sap/cloud/sdk/services/builder/api/SodasApi.java
index d3dedf9c6..792829ce8 100644
--- a/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/remove-operation-id-prefix/output/com/sap/cloud/sdk/services/builder/api/SodasApi.java
+++ b/datamodel/openapi/openapi-generator/src/test/resources/DataModelGeneratorApacheIntegrationTest/remove-operation-id-prefix/output/com/sap/cloud/sdk/services/builder/api/SodasApi.java
@@ -57,6 +57,19 @@ public SodasApi(@Nonnull final ApiClient apiClient) {
     super(apiClient);
     }
 
+    /**
+    * Creates a new API instance with additional default headers.
+    *
+    * @param defaultHeaders Additional headers to include in all requests
+    * @return A new API instance with the combined headers
+    */
+    public SodasApi withDefaultHeaders(@Nonnull final Map<String, String> defaultHeaders) {
+        final var api = new SodasApi(apiClient);
+        api.defaultHeaders.putAll(this.defaultHeaders);
+        api.defaultHeaders.putAll(defaultHeaders);
+        return api;
+    }
+
 
         /**
          * <p>Get all soda products
@@ -74,7 +87,7 @@ public List<SodaWithId> get() throws OpenApiRequestException {
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
             
                                     
@@ -130,7 +143,7 @@ public SodaWithId sodasIdGet(@Nonnull final Long id) throws OpenApiRequestExcept
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();
             
                                     
@@ -186,7 +199,7 @@ public Soda sodasPut(@Nonnull final SodaWithId sodaWithId) throws OpenApiRequest
             final StringJoiner localVarQueryStringJoiner = new StringJoiner("&");
             final List<Pair> localVarQueryParams = new ArrayList<Pair>();
             final List<Pair> localVarCollectionQueryParams = new ArrayList<Pair>();
-            final Map<String, String> localVarHeaderParams = new HashMap<String, String>();
+            final Map<String, String> localVarHeaderParams = new HashMap<String, String>(defaultHeaders);
             final Map<String, Object> localVarFormParams = new HashMap<String, Object>();