.Net: Bug: Inconsistent Handling of ResponseFormat Type in AzureOpenAIPromptExecutionSettings Between IChatCompletionService and IChatClient

[runceel]

Describe the bug
When using AzureOpenAIPromptExecutionSettings.ResponseFormat with a System.Type (e.g., typeof(Person)), there is inconsistent behavior between IChatCompletionService and IChatClient.

• IChatCompletionService returns structured output as expected.
• IChatClient throws a serialization exception:

Serialization and deserialization of 'System.RuntimeType' instances is not supported. The unsupported member type is located on type 'System.Object'. Path: $.ResponseFormat.
at System.Text.Json.ThrowHelper.ThrowNotSupportedException(WriteStack& state, Exception innerException)
at System.Text.Json.Serialization.JsonConverter1.WriteCore(Utf8JsonWriter writer, T& value, JsonSerializerOptions options, WriteStack& state)   at System.Text.Json.Serialization.Metadata.JsonTypeInfo1.Serialize(Utf8JsonWriter writer, T& rootValue, Object rootValueBoxed)
at System.Text.Json.Serialization.Metadata.JsonTypeInfo`1.SerializeAsObject(Utf8JsonWriter writer, Object rootValue)
at System.Text.Json.JsonSerializer.WriteStringAsObject(Object value, JsonTypeInfo jsonTypeInfo)
at Microsoft.SemanticKernel.PromptExecutionSettingsExtensions.ToChatOptions(PromptExecutionSettings settings, Kernel kernel)
at Program.<<Main>$>d__0.MoveNext() (Program.cs:line 36)

To Reproduce
Steps to reproduce the behavior:

1. Set up a Semantic Kernel project with both IChatCompletionService and IChatClient using Azure OpenAI.
2. Set ResponseFormat = typeof(Person) in AzureOpenAIPromptExecutionSettings.
3. Call both GetChatMessageContentAsync (via IChatCompletionService) and GetResponseAsync (via IChatClient).
4. Observe that IChatClient throws a serialization exception, while IChatCompletionService works as expected.

Expected behavior
Both IChatCompletionService and IChatClient should handle the ResponseFormat type consistently, enabling structured output and returning the result in JSON format.

Screenshots
N/A (see exception message above)

Platform

• Language: C#
• Source: NuGet package Microsoft.SemanticKernel 1.54.0,
• AI model: Azure OpenAI Service, gpt-4.1
• IDE: Visual Studio 2022
• OS: Windows 11

Additional context

This difference in behavior was noticed when switching from AddAzureOpenAIChatCompletion to AddAzureOpenAIChatClient while using ChatCompletionAgent, which resulted in the exception.

Minimal repro:

using Microsoft.Extensions.AI;
using Microsoft.SemanticKernel;
using Microsoft.SemanticKernel.ChatCompletion;
using Microsoft.SemanticKernel.Connectors.AzureOpenAI;

const string Endpoint = "<<your aoai endpoint>>";
const string DeploymentName = "<<your deployment model name>>";
const string ApiKey = "<<your api key>>";

var builder = Kernel.CreateBuilder();
builder.AddAzureOpenAIChatCompletion(
    DeploymentName,
    Endpoint,
    ApiKey,
    serviceId: "ChatCompletion");
builder.AddAzureOpenAIChatClient(
    DeploymentName,
    Endpoint,
    ApiKey,
    serviceId: "ChatClient");

var kernel = builder.Build();

IChatCompletionService chatCompletionService = kernel.GetRequiredService<IChatCompletionService>("ChatCompletion");
IChatClient chatClient = kernel.GetRequiredService<IChatClient>("ChatClient");

const string input = "My name is Jone Doe, I am 30 years old.";

var chatCompletionResponse = await chatCompletionService.GetChatMessageContentAsync(input,
    new AzureOpenAIPromptExecutionSettings
    {
        ResponseFormat = typeof(Person),
    });
Console.WriteLine(chatCompletionResponse.Content);

var chatClientResponse = await chatClient.GetResponseAsync([new ChatMessage(ChatRole.User, input)],
    options: new AzureOpenAIPromptExecutionSettings
    {
        ResponseFormat = typeof(Person),
    }.ToChatOptions(kernel));
Console.WriteLine(chatClientResponse.Text);

record Person(string Name, int Age);