.NET: [Bug]: Update OpenAI 2.9.1 to prevent MissingMethodException

[rstropek]

Description

The following code sample compiles without problems, but shows the following error during runtime:

MissingMethodException (expected with OpenAI 2.9.0):
Method not found: 'System.String OpenAI.Responses.ResponsesClient.get_Model()'.

Works with GetChatClient.

Code Sample

using Microsoft.Agents.AI;
using Microsoft.Extensions.AI;
using OpenAI;
using OpenAI.Responses;

// Minimal repro for:
//   System.MissingMethodException: Method not found:
//   'System.String OpenAI.Responses.ResponsesClient.get_Model()'
//
// Guess: Microsoft.Extensions.AI.OpenAI 10.3.0 was compiled against a future version
// of the OpenAI SDK that exposes ResponsesClient.Model, but OpenAI 2.9.0 (the
// latest public release) does not have that property.
//
// Calling AsAIAgent() on the ResponsesClient triggers the bridge code inside
// OpenAIResponsesChatClient..ctor which calls responseClient.Model, causing the
// MissingMethodException at runtime even though the code compiles fine.

var responsesClient = new OpenAIClient("dummy-key").GetResponsesClient();

try
{
    // This throws MissingMethodException at runtime:
    AIAgent agent = responsesClient.AsAIAgent(
        instructions: "You are a helpful assistant.",
        name: "TestAgent");

    Console.WriteLine("No exception — packages are compatible.");
}
catch (MissingMethodException ex)
{
    Console.WriteLine("MissingMethodException (expected with OpenAI 2.9.0):");
    Console.WriteLine(ex.Message);
}

Error Messages / Stack Traces

MissingMethodException (expected with OpenAI 2.9.0):
Method not found: 'System.String OpenAI.Responses.ResponsesClient.get_Model()'.

Package Versions

Microsoft.Agents.AI.OpenAI: 1.0.0-rc2, OpenAI: 2.9.0, Microsoft.Extensions.AI.OpenAI: 10.3.0

.NET Version

.NET 10

Additional Context

No response

[rogeriorfp]

Description

The following code sample compiles without problems, but shows the following error during runtime:

MissingMethodException (expected with OpenAI 2.9.0):
Method not found: 'System.String OpenAI.Responses.ResponsesClient.get_Model()'.
Works with GetChatClient.

Code Sample

using Microsoft.Agents.AI;
using Microsoft.Extensions.AI;
using OpenAI;
using OpenAI.Responses;

// Minimal repro for:
// System.MissingMethodException: Method not found:
// 'System.String OpenAI.Responses.ResponsesClient.get_Model()'
//
// Guess: Microsoft.Extensions.AI.OpenAI 10.3.0 was compiled against a future version
// of the OpenAI SDK that exposes ResponsesClient.Model, but OpenAI 2.9.0 (the
// latest public release) does not have that property.
//
// Calling AsAIAgent() on the ResponsesClient triggers the bridge code inside
// OpenAIResponsesChatClient..ctor which calls responseClient.Model, causing the
// MissingMethodException at runtime even though the code compiles fine.

var responsesClient = new OpenAIClient("dummy-key").GetResponsesClient();

try
{
// This throws MissingMethodException at runtime:
AIAgent agent = responsesClient.AsAIAgent(
instructions: "You are a helpful assistant.",
name: "TestAgent");

Console.WriteLine("No exception — packages are compatible.");

}
catch (MissingMethodException ex)
{
Console.WriteLine("MissingMethodException (expected with OpenAI 2.9.0):");
Console.WriteLine(ex.Message);
}

Error Messages / Stack Traces

MissingMethodException (expected with OpenAI 2.9.0):
Method not found: 'System.String OpenAI.Responses.ResponsesClient.get_Model()'.

Package Versions

Microsoft.Agents.AI.OpenAI: 1.0.0-rc2, OpenAI: 2.9.0, Microsoft.Extensions.AI.OpenAI: 10.3.0

.NET Version

.NET 10

Additional Context

No response

Since you are explicitly referencing OpenAI in your project, you are overriding the version against which Microsoft.Extensions.AI was compiled.

Microsoft.Extensions.AI was compiled against OpenAI version 2.8.0, while your project is directly referencing version 2.9.0.

You can either reference version 2.8.0 to match the expected dependency, or remove the explicit reference and allow the correct version to be resolved transitively.

[rstropek]

Thanks for the clarification. I could solve the problem by downgrading to 2.8.0.

In my project, I’m using both “traditional” AI integration with OpenAI directly and the Agent Framework side by side. That’s the reason for the explicit reference.

That said, I’m wondering whether the observed behavior might actually be considered a bug (in whichever library is responsible). From my understanding, changing only a minor version should not introduce breaking changes that result in a runtime exception.

[rogerbarreto]

@rstropek As you stated in the issue header, the problem happens in the Microsoft.Extensions.AI.OpenAI attempting to retrieve an experimental field

https://github.com/openai/openai-dotnet/blob/8639c48b359cb3b6b5b9e072116db68e73954717/src/Custom/Responses/ResponsesClient.cs#L118

Experimental features are allowed to break and that's exactly what happened, a new release of MEAI will soon resolve the issue and for now the recommendation is to stick with the 2.8.0 until we can update our packages downstream.

Tracking here to update as soon Microsoft Extensions AI OpenAI releases their next update with the 2.9.1 support.

• [BREAKING] Update OpenAI SDK to 2.9.1 #4424