diff --git a/dotnet/src/Microsoft.Agents.AI.AGUI/AGUIChatClient.cs b/dotnet/src/Microsoft.Agents.AI.AGUI/AGUIChatClient.cs
index ddaf6bd5929..0f4f1c290c6 100644
--- a/dotnet/src/Microsoft.Agents.AI.AGUI/AGUIChatClient.cs
+++ b/dotnet/src/Microsoft.Agents.AI.AGUI/AGUIChatClient.cs
@@ -214,6 +214,7 @@ public async IAsyncEnumerable<ChatResponseUpdate> GetStreamingResponseAsync(
                 RunId = runId,
                 Messages = messagesList.AsAGUIMessages(this._jsonSerializerOptions),
                 State = state,
+                ForwardedProperties = ExtractForwardedPropertiesFromOptions(options),
             };
 
             // Add tools if provided
@@ -288,6 +289,18 @@ public async IAsyncEnumerable<ChatResponseUpdate> GetStreamingResponseAsync(
             return threadId;
         }
 
+        private static JsonElement ExtractForwardedPropertiesFromOptions(ChatOptions? options)
+        {
+            if (options?.AdditionalProperties is null ||
+              !options.AdditionalProperties.TryGetValue("ag_ui_forwarded_properties", out object? forwardedProperties) ||
+              forwardedProperties is not JsonElement jsonElement)
+            {
+                return default;
+            }
+
+            return jsonElement;
+        }
+
         // Extract the session id from the second last message's function call content additional properties
         private static string? ExtractTemporaryThreadId(List<ChatMessage> messagesList)
         {
diff --git a/dotnet/tests/Microsoft.Agents.AI.AGUI.UnitTests/AGUIChatClientTests.cs b/dotnet/tests/Microsoft.Agents.AI.AGUI.UnitTests/AGUIChatClientTests.cs
index d5890bb5f20..856d7143b36 100644
--- a/dotnet/tests/Microsoft.Agents.AI.AGUI.UnitTests/AGUIChatClientTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.AGUI.UnitTests/AGUIChatClientTests.cs
@@ -1395,6 +1395,44 @@ public async Task GetStreamingResponseAsync_WithNoStateDataContent_SendsEmptySta
         Assert.Null(captureHandler.CapturedState);
     }
 
+    [Fact]
+    public async Task GetStreamingResponseAsync_ForwardsAdditionalPropertiesInRunInputAsync()
+    {
+        // Arrange
+        var forwardedProperties = new { tenant = "contoso", conversation = "abc123" };
+
+        var captureHandler = new StateCapturingTestDelegatingHandler();
+        captureHandler.AddResponse(
+        [
+            new RunStartedEvent { ThreadId = "thread1", RunId = "run1" },
+            new RunFinishedEvent { ThreadId = "thread1", RunId = "run1" }
+        ]);
+        using HttpClient httpClient = new(captureHandler);
+
+        var chatClient = new AGUIChatClient(httpClient, "http://localhost/agent", null, AGUIJsonSerializerContext.Default.Options);
+        var options = new ChatOptions
+        {
+            AdditionalProperties = new AdditionalPropertiesDictionary
+            {
+                ["ag_ui_forwarded_properties"] = JsonSerializer.SerializeToElement(forwardedProperties)
+            }
+        };
+        List<ChatMessage> messages = [new ChatMessage(ChatRole.User, "Hello")];
+
+        // Act
+        await foreach (var _ in chatClient.GetStreamingResponseAsync(messages, options))
+        {
+            // Just consume the stream
+        }
+
+        // Assert
+        Assert.True(captureHandler.RequestWasMade);
+        Assert.NotNull(captureHandler.CapturedForwardedProperties);
+        Assert.Equal(JsonValueKind.Object, captureHandler.CapturedForwardedProperties.Value.ValueKind);
+        Assert.Equal("contoso", captureHandler.CapturedForwardedProperties.Value.GetProperty("tenant").GetString());
+        Assert.Equal("abc123", captureHandler.CapturedForwardedProperties.Value.GetProperty("conversation").GetString());
+    }
+
     [Fact]
     public async Task GetStreamingResponseAsync_WithMalformedStateJson_ThrowsInvalidOperationExceptionAsync()
     {
@@ -1730,6 +1768,7 @@ internal sealed class StateCapturingTestDelegatingHandler : DelegatingHandler
 
     public bool RequestWasMade { get; private set; }
     public JsonElement? CapturedState { get; private set; }
+    public JsonElement? CapturedForwardedProperties { get; private set; }
     public int CapturedMessageCount { get; private set; }
     public IReadOnlyList<int> CapturedMessageCounts => this._capturedMessageCounts;
 
@@ -1755,6 +1794,10 @@ protected override async Task<HttpResponseMessage> SendAsync(HttpRequestMessage
             {
                 this.CapturedState = input.State;
             }
+            if (input.ForwardedProperties.ValueKind is not JsonValueKind.Undefined and not JsonValueKind.Null)
+            {
+                this.CapturedForwardedProperties = input.ForwardedProperties;
+            }
             this.CapturedMessageCount = input.Messages.Count();
             this._capturedMessageCounts.Add(this.CapturedMessageCount);
         }