diff --git a/dotnet/src/Agents/Abstractions/AgentInvokeOptions.cs b/dotnet/src/Agents/Abstractions/AgentInvokeOptions.cs
index 6aff36e0fc64..57d27652ab02 100644
--- a/dotnet/src/Agents/Abstractions/AgentInvokeOptions.cs
+++ b/dotnet/src/Agents/Abstractions/AgentInvokeOptions.cs
@@ -5,7 +5,7 @@ namespace Microsoft.SemanticKernel.Agents;
 /// <summary>
 /// Optional parameters for agent invocation.
 /// </summary>
-public class AgentInvokeOptions
+public sealed class AgentInvokeOptions
 {
     /// <summary>
     /// Gets or sets optional arguments to pass to the agent's invocation, including any <see cref="PromptExecutionSettings"/>
diff --git a/dotnet/src/Agents/Abstractions/AgentThread.cs b/dotnet/src/Agents/Abstractions/AgentThread.cs
index 9fe3ba7fa6b7..e229db0088f3 100644
--- a/dotnet/src/Agents/Abstractions/AgentThread.cs
+++ b/dotnet/src/Agents/Abstractions/AgentThread.cs
@@ -30,8 +30,8 @@ public abstract class AgentThread
     /// Creates the thread and returns the thread id.
     /// </summary>
     /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
-    /// <returns>The id of the new thread.</returns>
-    public virtual async Task<string> CreateAsync(CancellationToken cancellationToken = default)
+    /// <returns>A task that completes when the thread has been created.</returns>
+    public virtual async Task CreateAsync(CancellationToken cancellationToken = default)
     {
         if (this.IsDeleted)
         {
@@ -40,11 +40,10 @@ public virtual async Task<string> CreateAsync(CancellationToken cancellationToke
 
         if (this.Id is not null)
         {
-            return this.Id;
+            return;
         }
 
         this.Id = await this.CreateInternalAsync(cancellationToken: cancellationToken).ConfigureAwait(false);
-        return this.Id;
     }
 
     /// <summary>
@@ -98,8 +97,8 @@ public virtual async Task OnNewMessageAsync(ChatMessageContent newMessage, Cance
     /// Checks have already been completed in the <see cref="CreateAsync"/> method to ensure that the thread can be created.
     /// </summary>
     /// <param name="cancellationToken">The <see cref="CancellationToken"/> to monitor for cancellation requests. The default is <see cref="CancellationToken.None"/>.</param>
-    /// <returns>The id of the thread that was created.</returns>
-    protected abstract Task<string> CreateInternalAsync(CancellationToken cancellationToken);
+    /// <returns>The id of the thread that was created if one is available.</returns>
+    protected abstract Task<string?> CreateInternalAsync(CancellationToken cancellationToken);
 
     /// <summary>
     /// Deletes the current thread.
diff --git a/dotnet/src/Agents/AzureAI/AzureAIAgentThread.cs b/dotnet/src/Agents/AzureAI/AzureAIAgentThread.cs
index 519dec3ec43d..39bbcce4fbba 100644
--- a/dotnet/src/Agents/AzureAI/AzureAIAgentThread.cs
+++ b/dotnet/src/Agents/AzureAI/AzureAIAgentThread.cs
@@ -62,7 +62,7 @@ public AzureAIAgentThread(AgentsClient client, string id)
     }
 
     /// <inheritdoc />
-    protected async override Task<string> CreateInternalAsync(CancellationToken cancellationToken)
+    protected async override Task<string?> CreateInternalAsync(CancellationToken cancellationToken)
     {
         const string ErrorMessage = "The thread could not be created due to an error response from the service.";
 
diff --git a/dotnet/src/Agents/Core/ChatHistoryAgentThread.cs b/dotnet/src/Agents/Core/ChatHistoryAgentThread.cs
index 653f3b6e423f..313bdff31fcb 100644
--- a/dotnet/src/Agents/Core/ChatHistoryAgentThread.cs
+++ b/dotnet/src/Agents/Core/ChatHistoryAgentThread.cs
@@ -37,9 +37,9 @@ public ChatHistoryAgentThread(ChatHistory chatHistory, string? id = null)
     }
 
     /// <inheritdoc />
-    protected override Task<string> CreateInternalAsync(CancellationToken cancellationToken)
+    protected override Task<string?> CreateInternalAsync(CancellationToken cancellationToken)
     {
-        return Task.FromResult(Guid.NewGuid().ToString("N"));
+        return Task.FromResult<string?>(Guid.NewGuid().ToString("N"));
     }
 
     /// <inheritdoc />
diff --git a/dotnet/src/Agents/OpenAI/OpenAIAssistantAgentThread.cs b/dotnet/src/Agents/OpenAI/OpenAIAssistantAgentThread.cs
index 37e95a763407..97952a8f1fed 100644
--- a/dotnet/src/Agents/OpenAI/OpenAIAssistantAgentThread.cs
+++ b/dotnet/src/Agents/OpenAI/OpenAIAssistantAgentThread.cs
@@ -48,7 +48,7 @@ public OpenAIAssistantAgentThread(AssistantClient client, string id)
     }
 
     /// <inheritdoc />
-    protected async override Task<string> CreateInternalAsync(CancellationToken cancellationToken)
+    protected async override Task<string?> CreateInternalAsync(CancellationToken cancellationToken)
     {
         const string ErrorMessage = "The thread could not be created due to an error response from the service.";