.Net: Bug: Function call with complex objects fails with o3-mini

[AlesRuzickaEu]

Describe the bug
Function call with complex object and optional values fail with o3-mini (works with gpt-4o)

To Reproduce

Minimal code:

var builder = Kernel
    .CreateBuilder();

builder.AddOpenAIChatCompletion("o3-mini", apiKey);

var kernel = builder.Build();

kernel.Plugins.AddFromType<Plugin>("Plugin");

var chatCompletionServices = kernel.GetRequiredService<IChatCompletionService>();

var promptExecutionSettings = new OpenAIPromptExecutionSettings
{
    FunctionChoiceBehavior = FunctionChoiceBehavior.Required(options: new FunctionChoiceBehaviorOptions
    {
        AllowStrictSchemaAdherence = true,
    })
};

var history = new ChatHistory();

history.AddUserMessage("Generate name as 'a'");

var result = await chatCompletionServices.GetChatMessageContentAsync(history, promptExecutionSettings, kernel);

class Plugin
{
    [KernelFunction("generate")]
    public void Generate(Result result)
    {
    }
}

public class Result
{
    public string? Name { get; set; }
}

Expected behavior
Expect function call with complex object

Actual behavior
Throws Error:
Microsoft.SemanticKernel.HttpOperationException: 'HTTP 400 (invalid_request_error: )

Invalid schema for function 'Plugin-generate': In context=('properties', 'result', 'properties', 'Name'), schema must have a 'type' key.'

Platform

• Language: C#
• Source: NuGet package version 1.45.0
• AI model: OpenAI:o3-mini
• IDE: Visual Studio
• OS: Windows

Additional context
Add any other context about the problem here.

[SergeyMenshykh]

Hi @AlesRuzickaEu, for some reason "o3-mini" fails when the strict mode is enabled, even though a few other models that support the strict mode work perfectly fine. The produced schema for the function parameters is fully compatible with the one required by the strict mode:

{
  "type": "object",
  "required": [
    "result"
  ],
  "properties": {
    "result": {
      "type": "object",
      "properties": {
        "Name": {
          "type": [
            "string",
            "null"
          ]
        }
      },
      "additionalProperties": false,
      "required": [
        "Name"
      ]
    }
  },
  "additionalProperties": false
}

So, at the moment, you have two options:

1. Change the model to a different one that supports the structured output and does not fail when it's enabled.
2. Disable the strict mode:
   FunctionChoiceBehavior = FunctionChoiceBehavior.Required(options: new FunctionChoiceBehaviorOptions { AllowStrictSchemaAdherence = false })
   or just
   FunctionChoiceBehavior = FunctionChoiceBehavior.Required()

[AlesRuzickaEu]

What worked for me is making everything required.
Then it works fine even with strict mode.
There seems to be some issue with "null" options.
I just wondered if there is not other way here, maybe some change in definition.

[SergeyMenshykh]

Yep, making the Result.Name not nullable worked for me as well. I saw a few posts on the internet where people complain about the same issue. It may be worth opening an issue/thread on the OpenAI dev forum.