diff --git a/foundation-models/openai/pom.xml b/foundation-models/openai/pom.xml
index 8846896f3..998b89dc1 100644
--- a/foundation-models/openai/pom.xml
+++ b/foundation-models/openai/pom.xml
@@ -38,11 +38,11 @@
   </scm>
   <properties>
     <project.rootdir>${project.basedir}/../../</project.rootdir>
-    <coverage.complexity>71%</coverage.complexity>
+    <coverage.complexity>70%</coverage.complexity>
     <coverage.line>80%</coverage.line>
     <coverage.instruction>76%</coverage.instruction>
     <coverage.branch>70%</coverage.branch>
-    <coverage.method>76%</coverage.method>
+    <coverage.method>75%</coverage.method>
     <coverage.class>84%</coverage.class>
   </properties>
   <dependencies>
diff --git a/foundation-models/openai/src/main/java/com/sap/ai/sdk/foundationmodels/openai/OpenAiAssistantMessage.java b/foundation-models/openai/src/main/java/com/sap/ai/sdk/foundationmodels/openai/OpenAiAssistantMessage.java
index c77f1044d..26fe6d8b9 100644
--- a/foundation-models/openai/src/main/java/com/sap/ai/sdk/foundationmodels/openai/OpenAiAssistantMessage.java
+++ b/foundation-models/openai/src/main/java/com/sap/ai/sdk/foundationmodels/openai/OpenAiAssistantMessage.java
@@ -1,6 +1,6 @@
 package com.sap.ai.sdk.foundationmodels.openai;
 
-import static lombok.AccessLevel.PUBLIC;
+import static lombok.AccessLevel.PACKAGE;
 
 import com.google.common.annotations.Beta;
 import com.sap.ai.sdk.foundationmodels.openai.generated.model.ChatCompletionMessageToolCall;
@@ -8,6 +8,7 @@
 import com.sap.ai.sdk.foundationmodels.openai.generated.model.ChatCompletionRequestAssistantMessage;
 import com.sap.ai.sdk.foundationmodels.openai.generated.model.ChatCompletionRequestAssistantMessageContent;
 import com.sap.ai.sdk.foundationmodels.openai.generated.model.ToolCallType;
+import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
 import javax.annotation.Nonnull;
@@ -28,7 +29,7 @@
 @Beta
 @Value
 @Accessors(fluent = true)
-@AllArgsConstructor(access = PUBLIC)
+@AllArgsConstructor(access = PACKAGE)
 public class OpenAiAssistantMessage implements OpenAiMessage {
 
   /** The role associated with this message. */
@@ -52,12 +53,27 @@ public class OpenAiAssistantMessage implements OpenAiMessage {
   @Nonnull
   List<OpenAiToolCall> toolCalls;
 
+  /**
+   * Creates a new assistant message with the given content and additional tool calls.
+   *
+   * @param toolCalls the additional tool calls to associate with the message.
+   * @return a new assistant message with the given content and additional tool calls.
+   * @since 1.10.0
+   */
+  @Nonnull
+  public OpenAiAssistantMessage withToolCalls(
+      @Nonnull final List<? extends OpenAiToolCall> toolCalls) {
+    final List<OpenAiToolCall> newToolCalls = new ArrayList<>(this.toolCalls);
+    newToolCalls.addAll(toolCalls);
+    return new OpenAiAssistantMessage(content, newToolCalls);
+  }
+
   /**
    * Creates a new assistant message with the given single message as text content.
    *
    * @param singleMessage the message.
    */
-  public OpenAiAssistantMessage(@Nonnull final String singleMessage) {
+  OpenAiAssistantMessage(@Nonnull final String singleMessage) {
     this(
         new OpenAiMessageContent(List.of(new OpenAiTextItem(singleMessage))),
         Collections.emptyList());
diff --git a/foundation-models/openai/src/main/java/com/sap/ai/sdk/foundationmodels/openai/OpenAiFunctionCall.java b/foundation-models/openai/src/main/java/com/sap/ai/sdk/foundationmodels/openai/OpenAiFunctionCall.java
index 8075cb01b..c3668d26b 100644
--- a/foundation-models/openai/src/main/java/com/sap/ai/sdk/foundationmodels/openai/OpenAiFunctionCall.java
+++ b/foundation-models/openai/src/main/java/com/sap/ai/sdk/foundationmodels/openai/OpenAiFunctionCall.java
@@ -2,7 +2,6 @@
 
 import com.google.common.annotations.Beta;
 import javax.annotation.Nonnull;
-import lombok.AccessLevel;
 import lombok.AllArgsConstructor;
 import lombok.Value;
 
@@ -13,7 +12,7 @@
  */
 @Beta
 @Value
-@AllArgsConstructor(access = AccessLevel.PUBLIC)
+@AllArgsConstructor(access = lombok.AccessLevel.PACKAGE)
 public class OpenAiFunctionCall implements OpenAiToolCall {
   /** The unique identifier for the function call. */
   @Nonnull String id;
diff --git a/foundation-models/openai/src/main/java/com/sap/ai/sdk/foundationmodels/openai/OpenAiToolCall.java b/foundation-models/openai/src/main/java/com/sap/ai/sdk/foundationmodels/openai/OpenAiToolCall.java
index 9c400c4f4..9a4d3ff27 100644
--- a/foundation-models/openai/src/main/java/com/sap/ai/sdk/foundationmodels/openai/OpenAiToolCall.java
+++ b/foundation-models/openai/src/main/java/com/sap/ai/sdk/foundationmodels/openai/OpenAiToolCall.java
@@ -1,6 +1,7 @@
 package com.sap.ai.sdk.foundationmodels.openai;
 
 import com.google.common.annotations.Beta;
+import javax.annotation.Nonnull;
 
 /**
  * Represents a tool called by an OpenAI model.
@@ -8,4 +9,19 @@
  * @since 1.6.0
  */
 @Beta
-public sealed interface OpenAiToolCall permits OpenAiFunctionCall {}
+public sealed interface OpenAiToolCall permits OpenAiFunctionCall {
+  /**
+   * Creates a new instance of {@link OpenAiToolCall}.
+   *
+   * @param id The unique identifier for the tool call.
+   * @param name The name of the tool to be called.
+   * @param arguments The arguments for the tool call, encoded as a JSON string.
+   * @return A new instance of {@link OpenAiToolCall}.
+   * @since 1.10.0
+   */
+  @Nonnull
+  static OpenAiToolCall function(
+      @Nonnull final String id, @Nonnull final String name, @Nonnull final String arguments) {
+    return new OpenAiFunctionCall(id, name, arguments);
+  }
+}
diff --git a/foundation-models/openai/src/main/java/com/sap/ai/sdk/foundationmodels/openai/spring/OpenAiChatModel.java b/foundation-models/openai/src/main/java/com/sap/ai/sdk/foundationmodels/openai/spring/OpenAiChatModel.java
index efef63d5c..2d7dee093 100644
--- a/foundation-models/openai/src/main/java/com/sap/ai/sdk/foundationmodels/openai/spring/OpenAiChatModel.java
+++ b/foundation-models/openai/src/main/java/com/sap/ai/sdk/foundationmodels/openai/spring/OpenAiChatModel.java
@@ -2,14 +2,10 @@
 
 import static org.springframework.ai.model.tool.ToolCallingChatOptions.isInternalToolExecutionEnabled;
 
-import com.sap.ai.sdk.foundationmodels.openai.OpenAiAssistantMessage;
 import com.sap.ai.sdk.foundationmodels.openai.OpenAiChatCompletionRequest;
 import com.sap.ai.sdk.foundationmodels.openai.OpenAiChatCompletionResponse;
 import com.sap.ai.sdk.foundationmodels.openai.OpenAiClient;
-import com.sap.ai.sdk.foundationmodels.openai.OpenAiFunctionCall;
 import com.sap.ai.sdk.foundationmodels.openai.OpenAiMessage;
-import com.sap.ai.sdk.foundationmodels.openai.OpenAiMessageContent;
-import com.sap.ai.sdk.foundationmodels.openai.OpenAiTextItem;
 import com.sap.ai.sdk.foundationmodels.openai.OpenAiToolCall;
 import com.sap.ai.sdk.foundationmodels.openai.generated.model.ChatCompletionMessageToolCall;
 import com.sap.ai.sdk.foundationmodels.openai.generated.model.ChatCompletionResponseMessage;
@@ -86,10 +82,9 @@ private static void addAssistantMessage(
       return;
     }
     final Function<ToolCall, OpenAiToolCall> callTranslate =
-        toolCall -> new OpenAiFunctionCall(toolCall.id(), toolCall.name(), toolCall.arguments());
-    val content = new OpenAiMessageContent(List.of(new OpenAiTextItem(message.getText())));
+        toolCall -> OpenAiToolCall.function(toolCall.id(), toolCall.name(), toolCall.arguments());
     val calls = message.getToolCalls().stream().map(callTranslate).toList();
-    result.add(new OpenAiAssistantMessage(content, calls));
+    result.add(OpenAiMessage.assistant(message.getText()).withToolCalls(calls));
   }
 
   private static void addToolMessages(