diff --git a/models/spring-ai-mistral-ai/src/main/java/org/springframework/ai/mistralai/MistralAiChatModel.java b/models/spring-ai-mistral-ai/src/main/java/org/springframework/ai/mistralai/MistralAiChatModel.java
index 98376720f2d..d9441bacaec 100644
--- a/models/spring-ai-mistral-ai/src/main/java/org/springframework/ai/mistralai/MistralAiChatModel.java
+++ b/models/spring-ai-mistral-ai/src/main/java/org/springframework/ai/mistralai/MistralAiChatModel.java
@@ -380,7 +380,7 @@ else if (message instanceof AssistantMessage assistantMessage) {
 				if (!CollectionUtils.isEmpty(assistantMessage.getToolCalls())) {
 					toolCalls = assistantMessage.getToolCalls().stream().map(toolCall -> {
 						var function = new ChatCompletionFunction(toolCall.name(), toolCall.arguments());
-						return new ToolCall(toolCall.id(), toolCall.type(), function);
+						return new ToolCall(toolCall.id(), toolCall.type(), function, null);
 					}).toList();
 				}
 
diff --git a/models/spring-ai-mistral-ai/src/main/java/org/springframework/ai/mistralai/api/MistralAiApi.java b/models/spring-ai-mistral-ai/src/main/java/org/springframework/ai/mistralai/api/MistralAiApi.java
index 433ace72b7f..2b14a1db181 100644
--- a/models/spring-ai-mistral-ai/src/main/java/org/springframework/ai/mistralai/api/MistralAiApi.java
+++ b/models/spring-ai-mistral-ai/src/main/java/org/springframework/ai/mistralai/api/MistralAiApi.java
@@ -824,10 +824,11 @@ public enum Role {
 		 * @param type The type of tool call the output is required for. For now, this is
 		 * always function.
 		 * @param function The function definition.
+		 * @param index The index of the tool call in the list of tool calls.
 		 */
 		@JsonInclude(Include.NON_NULL)
 		public record ToolCall(@JsonProperty("id") String id, @JsonProperty("type") String type,
-				@JsonProperty("function") ChatCompletionFunction function) {
+				@JsonProperty("function") ChatCompletionFunction function, @JsonProperty("index") Integer index) {
 
 		}
 
diff --git a/models/spring-ai-mistral-ai/src/main/java/org/springframework/ai/mistralai/api/MistralAiStreamFunctionCallingHelper.java b/models/spring-ai-mistral-ai/src/main/java/org/springframework/ai/mistralai/api/MistralAiStreamFunctionCallingHelper.java
index 608e8d6ffbb..079edfa988b 100644
--- a/models/spring-ai-mistral-ai/src/main/java/org/springframework/ai/mistralai/api/MistralAiStreamFunctionCallingHelper.java
+++ b/models/spring-ai-mistral-ai/src/main/java/org/springframework/ai/mistralai/api/MistralAiStreamFunctionCallingHelper.java
@@ -16,10 +16,7 @@
 
 package org.springframework.ai.mistralai.api;
 
-import java.util.ArrayList;
-import java.util.List;
-import java.util.Optional;
-import java.util.UUID;
+import java.util.*;
 
 import org.springframework.ai.mistralai.api.MistralAiApi.ChatCompletionChunk;
 import org.springframework.ai.mistralai.api.MistralAiApi.ChatCompletionChunk.ChunkChoice;
@@ -74,16 +71,16 @@ private ChunkChoice merge(ChunkChoice previous, ChunkChoice current) {
 				Optional<String> id = current.delta()
 					.toolCalls()
 					.stream()
-					.filter(tool -> tool.id() != null)
-					.map(tool -> tool.id())
+					.map(ToolCall::id)
+					.filter(Objects::nonNull)
 					.findFirst();
-				if (!id.isPresent()) {
+				if (id.isEmpty()) {
 					var newId = UUID.randomUUID().toString();
 
 					var toolCallsWithID = current.delta()
 						.toolCalls()
 						.stream()
-						.map(toolCall -> new ToolCall(newId, "function", toolCall.function()))
+						.map(toolCall -> new ToolCall(newId, "function", toolCall.function(), toolCall.index()))
 						.toList();
 
 					var role = current.delta().role() != null ? current.delta().role() : Role.ASSISTANT;
@@ -151,7 +148,8 @@ private ToolCall merge(ToolCall previous, ToolCall current) {
 		String id = (current.id() != null ? current.id() : previous.id());
 		String type = (current.type() != null ? current.type() : previous.type());
 		ChatCompletionFunction function = merge(previous.function(), current.function());
-		return new ToolCall(id, type, function);
+		Integer index = (current.index() != null ? current.index() : previous.index());
+		return new ToolCall(id, type, function, index);
 	}
 
 	private ChatCompletionFunction merge(ChatCompletionFunction previous, ChatCompletionFunction current) {