diff --git a/dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/ChatCompletions/Models/StopSequences.cs b/dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/ChatCompletions/Models/StopSequences.cs
index bed3b2a3206..3a97f2f19b0 100644
--- a/dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/ChatCompletions/Models/StopSequences.cs
+++ b/dotnet/src/Microsoft.Agents.AI.Hosting.OpenAI/ChatCompletions/Models/StopSequences.cs
@@ -183,7 +183,7 @@ public override void Write(Utf8JsonWriter writer, StopSequences? value, JsonSeri
         }
         else if (value.IsSequences)
         {
-            JsonSerializer.Serialize(writer, value.Sequences, ChatCompletionsJsonContext.Default.IReadOnlyListMessageContentPart);
+            JsonSerializer.Serialize(writer, value.Sequences, ChatCompletionsJsonContext.Default.IListString);
         }
         else
         {
diff --git a/dotnet/tests/Microsoft.Agents.AI.Hosting.OpenAI.UnitTests/OpenAIChatCompletionsSerializationTests.cs b/dotnet/tests/Microsoft.Agents.AI.Hosting.OpenAI.UnitTests/OpenAIChatCompletionsSerializationTests.cs
index edf11fbf6bb..86e9292d62b 100644
--- a/dotnet/tests/Microsoft.Agents.AI.Hosting.OpenAI.UnitTests/OpenAIChatCompletionsSerializationTests.cs
+++ b/dotnet/tests/Microsoft.Agents.AI.Hosting.OpenAI.UnitTests/OpenAIChatCompletionsSerializationTests.cs
@@ -54,6 +54,25 @@ public void Deserialize_BasicRequest_RoundTrip()
         Assert.Equal(request.Messages.Count, roundtripped.Messages.Count);
     }
 
+    [Fact]
+    public void Serialize_RequestWithMultipleStopSequences_WritesStringArray()
+    {
+        // Arrange
+        string originalJson = LoadChatCompletionsTraceFile("basic/request.json");
+        CreateChatCompletion request = JsonSerializer.Deserialize(originalJson, ChatCompletions.ChatCompletionsJsonContext.Default.CreateChatCompletion)!;
+        request.Stop = StopSequences.FromSequences(["END", "STOP"]);
+
+        // Act
+        string json = JsonSerializer.Serialize(request, ChatCompletions.ChatCompletionsJsonContext.Default.CreateChatCompletion);
+        using JsonDocument document = JsonDocument.Parse(json);
+
+        // Assert
+JsonElement stop = document.RootElement.GetProperty("stop");
+Assert.Equal(JsonValueKind.Array, stop.ValueKind);
+string[] stopValues = stop.EnumerateArray().Select(static e => e.GetString()!).ToArray();
+Assert.Equal(["END", "STOP"], stopValues);
+    }
+
     [Fact]
     public void Deserialize_BasicRequest_HasMessages()
     {