fix (AzureOpenAI): ChatModel streaming response

  - Include `model` and `ServiceTier` information when merging the chat completion response
  - Add test to validate the model value

Resolves #4715

Auto-cherry-pick to 1.0.x

Signed-off-by: Ilayaperumal Gopinathan <ilayaperumal.gopinathan@broadcom.com>

Author: ilayaperumalg

models/spring-ai-azure-openai/src/main/java/org/springframework/ai/azure/openai/MergeUtils.java

@@ -168,6 +168,11 @@ public static ChatCompletions mergeChatCompletions(ChatCompletions left, ChatCom
 
 		setField(instance, "usage", usage);
 
+		setField(instance, "model", right.getModel() == null ? left.getModel() : right.getModel());
+
+		setField(instance, "serviceTier",
+				right.getServiceTier() == null ? left.getServiceTier() : right.getServiceTier());
+
 		return instance;
 	}
 

models/spring-ai-azure-openai/src/test/java/org/springframework/ai/azure/openai/AzureOpenAiChatModelIT.java

@@ -32,6 +32,7 @@
 import org.junit.jupiter.api.Test;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
+import reactor.core.publisher.Flux;
 
 import org.springframework.ai.chat.client.ChatClient;
 import org.springframework.ai.chat.messages.AssistantMessage;
@@ -409,6 +410,47 @@ void testMaxTokensForNonReasoningModels() {
 		}
 	}
 
+	@Test
+	void testModelInStreamingResponse() {
+		String prompt = "List three colors of the rainbow.";
+
+		// @formatter:off
+		Flux<ChatResponse> responseFlux = ChatClient.create(this.chatModel).prompt()
+				.options(AzureOpenAiChatOptions.builder()
+						.deploymentName("gpt-4o")
+						.build())
+				.user(prompt)
+				.stream()
+				.chatResponse();
+		// @formatter:on
+
+		List<ChatResponse> responses = responseFlux.collectList().block();
+
+		assertThat(responses).isNotEmpty();
+
+		ChatResponse lastResponse = responses.get(responses.size() - 1);
+
+		// Verify that the final merged response has model metadata
+		assertThat(lastResponse.getMetadata()).as("Last response should have metadata").isNotNull();
+		assertThat(lastResponse.getMetadata().getModel()).as("Last response metadata should contain model").isNotNull();
+
+		String model = lastResponse.getMetadata().getModel();
+		logger.info("Final merged response model: {}", model);
+		assertThat(model).isNotEmpty();
+		// Azure OpenAI models typically contain "gpt" in their name
+		assertThat(model).containsIgnoringCase("gpt");
+
+		String content = responses.stream()
+			.flatMap(r -> r.getResults().stream())
+			.map(Generation::getOutput)
+			.map(AssistantMessage::getText)
+			.filter(Objects::nonNull)
+			.collect(Collectors.joining());
+
+		assertThat(content).isNotEmpty();
+		logger.info("Generated content: {}", content);
+	}
+
 	record ActorsFilms(String actor, List<String> movies) {
 
 	}