[Microsoft.Extensions.AI.OpenAI] Streaming throws on Azure content-filter chunks with null delta (10.10.1)

Start in src/Libraries/Microsoft.Extensions.AI.OpenAI/OpenAIChatClient.cs, specifically TryGetReasoningContent and its callers, then run the credential-free dotnet run --project Repro.csproj reproduction. Done means annotation-only streaming choices with a null delta no longer throw, and the sequence prints TEXT: OK, FINISH: stop, and COMPLETED while remaining stream events stay consumable.

Description

Microsoft.Extensions.AI.OpenAI throws InvalidOperationException while reading Azure OpenAI Chat Completions streams when a content-filter annotation has a choice but no delta.

Azure can send these annotation-only events both between text chunks and after the finish_reason: "stop" chunk. Consequently, an application can display the complete answer and then fail while finishing enumeration. These are normal filter results (filtered: false, severity: "safe"), not failed requests or blocked content.

Reproduced with the latest NuGet packages:

• Microsoft.Extensions.AI.OpenAI 10.10.1
• OpenAI 2.14.0

Also observed with Microsoft.Extensions.AI.OpenAI 10.10.0 + OpenAI 2.13.0. A live Azure call using 10.10.1 + 2.14.0 returned HTTP 200 and emitted 994 text characters before failing with this exception. The credential-free reproduction below demonstrates the failure after the final text and stop chunk.

Reproduction Steps

No Azure resource, credentials, or network request is required. The handler supplies a minimal SSE sequence reproducing the annotation shape observed on Azure.

Create Repro.csproj:

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net10.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>
  <ItemGroup>
    <PackageReference Include="Microsoft.Extensions.AI.OpenAI" Version="10.10.1" />
    <PackageReference Include="OpenAI" Version="2.14.0" />
  </ItemGroup>
</Project>

Create Program.cs:

using System.ClientModel;
using System.ClientModel.Primitives;
using System.Net;
using System.Text;
using Microsoft.Extensions.AI;
using OpenAI;
using OpenAI.Chat;

using var http = new HttpClient(new SseHandler());
var sdk = new ChatClient("example-model", new ApiKeyCredential("not-a-real-key"), new OpenAIClientOptions
{
    Endpoint = new Uri("https://example.invalid/openai/v1"),
    Transport = new HttpClientPipelineTransport(http)
});
using var client = sdk.AsIChatClient();

try
{
    await foreach (var update in client.GetStreamingResponseAsync("Hello"))
    {
        if (update.Text.Length > 0)
            Console.WriteLine("TEXT: " + update.Text);
        if (update.FinishReason is not null)
            Console.WriteLine("FINISH: " + update.FinishReason);
    }
    Console.WriteLine("COMPLETED");
}
catch (Exception error)
{
    Console.WriteLine(error.GetType().FullName + ": " + error.Message);
    Console.WriteLine(error.StackTrace);
    Environment.ExitCode = 1;
}

sealed class SseHandler : HttpMessageHandler
{
    protected override Task<HttpResponseMessage> SendAsync(HttpRequestMessage request, CancellationToken cancellationToken)
    {
        const string sse = """
            data: {"id":"chatcmpl-example","object":"chat.completion.chunk","created":0,"model":"example-model","choices":[{"index":0,"delta":{"role":"assistant","content":"OK"},"finish_reason":null}]}

            data: {"id":"chatcmpl-example","object":"chat.completion.chunk","created":0,"model":"example-model","choices":[{"index":0,"delta":{},"finish_reason":"stop"}]}

            data: {"choices":[{"content_filter_offsets":{"check_offset":2,"start_offset":0,"end_offset":2},"content_filter_results":{"hate":{"filtered":false,"severity":"safe"}},"finish_reason":null,"index":0}],"created":0,"id":"","model":"","object":""}

            data: [DONE]


            """;
        return Task.FromResult(new HttpResponseMessage(HttpStatusCode.OK)
        {
            Content = new StringContent(sse, Encoding.UTF8, "text/event-stream")
        });
    }
}

Run:

dotnet run --project Repro.csproj

Expected behavior

The adapter should treat an annotation-only choice as containing no reasoning delta and continue enumeration normally. The reproduction should print TEXT: OK, FINISH: stop, and COMPLETED.

In real streams, later text, content-filter annotations, and the final usage chunk should remain consumable. Stopping enumeration at the first finish reason would lose trailing filter/usage events and would not handle annotations occurring mid-response.

Actual behavior

The reproduction prints:

TEXT: OK
FINISH: stop
System.InvalidOperationException: The requested operation requires an element of type 'Object', but the target element has type 'Null'.
   at System.Text.Json.ThrowHelper.ThrowJsonElementWrongTypeException(JsonTokenType expectedType, JsonTokenType actualType)
   at System.Text.Json.JsonDocument.TryGetNamedPropertyValue(Int32 index, ReadOnlySpan`1 propertyName, JsonElement& value)
   at Microsoft.Extensions.AI.OpenAIChatClient.TryGetReasoningContent(JsonPatch& patch, ReadOnlySpan`1 container, String& reasoningText)
   at Microsoft.Extensions.AI.OpenAIChatClient.TryGetReasoningDelta(StreamingChatCompletionUpdate update, String& reasoningText)

COMPLETED is never printed; the process exits with code 1. No reasoning options are needed to trigger the exception.

Root cause / suggested fix

In TryGetReasoningContent in the 10.10.1 source, the adapter checks that choices is a nonempty array and the delta property exists, but does not check that the property's value is an object before calling TryGetProperty on it.

The underlying OpenAI SDK represents the missing delta as "delta": null when exposing the choice through JsonPatch. Consequently, this condition succeeds:

doc.RootElement[0].TryGetProperty(container, out JsonElement containerElement)

but the next condition throws:

containerElement.TryGetProperty("reasoning_content"u8, out JsonElement reasoningElement)

Suggested change: require an object before examining reasoning fields:

doc.RootElement[0].TryGetProperty(container, out JsonElement containerElement) &&
containerElement.ValueKind == JsonValueKind.Object &&
containerElement.TryGetProperty("reasoning_content"u8, out JsonElement reasoningElement)

This guard was also absent from main when checked. The change above is a suggested fix; this report verifies the failing released packages, not a patched build.

Related issues / regression context

• #7726 introduced this helper as a workaround for openai/openai-dotnet#1281. That issue concerns an empty choices array; this report concerns a nonempty choices array with a null delta.
• openai/openai-dotnet#198 documents the same Azure annotation shape, but the historical fix was in the underlying OpenAI SDK. The exception reported here is in the Extensions AI adapter.

Configuration

• .NET SDK 10.0.401, target framework net10.0
• macOS, arm64
• Microsoft.Extensions.AI.OpenAI 10.10.1 (source commit 59e1741f6fb45cf7ae08e2df088aef71537a7bc4)
• OpenAI 2.14.0
• Live scenario: Azure OpenAI v1 Chat Completions, streaming with asynchronous content-filter annotations