diff --git a/shell/agents/AIShell.OpenAI.Agent/GPT.cs b/shell/agents/AIShell.OpenAI.Agent/GPT.cs
index 8d726cec..239f286b 100644
--- a/shell/agents/AIShell.OpenAI.Agent/GPT.cs
+++ b/shell/agents/AIShell.OpenAI.Agent/GPT.cs
@@ -9,6 +9,7 @@ internal enum EndpointType
 {
     AzureOpenAI,
     OpenAI,
+    CompatibleThirdParty,
 }
 
 public class GPT
@@ -56,9 +57,16 @@ public GPT(
         bool noDeployment = string.IsNullOrEmpty(Deployment);
         Type = noEndpoint && noDeployment
             ? EndpointType.OpenAI
-            : !noEndpoint && !noDeployment
-                ? EndpointType.AzureOpenAI
-                : throw new InvalidOperationException($"Invalid setting: {(noEndpoint ? "Endpoint" : "Deployment")} key is missing. To use Azure OpenAI service, please specify both the 'Endpoint' and 'Deployment' keys. To use OpenAI service, please ignore both keys.");
+            : !noEndpoint && noDeployment
+                ? EndpointType.CompatibleThirdParty
+                : !noEndpoint && !noDeployment
+                    ? EndpointType.AzureOpenAI
+                    : throw new InvalidOperationException($"Invalid setting: 'Deployment' key present but 'Endpoint' key is missing. To use Azure OpenAI service, please specify both the 'Endpoint' and 'Deployment' keys. To use OpenAI service, please ignore both keys.");
+
+        if (ModelInfo is null && Type is EndpointType.CompatibleThirdParty)
+        {
+            ModelInfo = ModelInfo.ThirdPartyModel;
+        }
     }
 
     /// <summary>
@@ -142,11 +150,18 @@ private void ShowEndpointInfo(IHost host)
                     new(label: "  Model", m => m.ModelName),
                 },
 
-            EndpointType.OpenAI => new CustomElement<GPT>[]
-                {
+            EndpointType.OpenAI =>
+                [
                     new(label: "  Type", m => m.Type.ToString()),
                     new(label: "  Model", m => m.ModelName),
-                },
+                ],
+
+            EndpointType.CompatibleThirdParty =>
+                [
+                    new(label: "  Type", m => m.Type.ToString()),
+                    new(label: "  Endpoint", m => m.Endpoint),
+                    new(label: "  Model", m => m.ModelName),
+                ],
 
             _ => throw new UnreachableException(),
         };
diff --git a/shell/agents/AIShell.OpenAI.Agent/ModelInfo.cs b/shell/agents/AIShell.OpenAI.Agent/ModelInfo.cs
index 654f090d..79674e85 100644
--- a/shell/agents/AIShell.OpenAI.Agent/ModelInfo.cs
+++ b/shell/agents/AIShell.OpenAI.Agent/ModelInfo.cs
@@ -13,6 +13,11 @@ internal class ModelInfo
     private static readonly Dictionary<string, ModelInfo> s_modelMap;
     private static readonly Dictionary<string, Task<Tokenizer>> s_encodingMap;
 
+    // A rough estimate to cover all third-party models.
+    //  - most popular models today support 32K+ context length;
+    //  - use the gpt-4o encoding as an estimate for token count.
+    internal static readonly ModelInfo ThirdPartyModel = new(32_000, encoding: Gpt4oEncoding);
+
     static ModelInfo()
     {
         // For reference, see https://platform.openai.com/docs/models and the "Counting tokens" section in
diff --git a/shell/agents/AIShell.OpenAI.Agent/Service.cs b/shell/agents/AIShell.OpenAI.Agent/Service.cs
index 583a90d6..9251a6f6 100644
--- a/shell/agents/AIShell.OpenAI.Agent/Service.cs
+++ b/shell/agents/AIShell.OpenAI.Agent/Service.cs
@@ -122,9 +122,10 @@ private void RefreshOpenAIClient()
             return;
         }
 
+        EndpointType type = _gptToUse.Type;
         string userKey = Utils.ConvertFromSecureString(_gptToUse.Key);
 
-        if (_gptToUse.Type is EndpointType.AzureOpenAI)
+        if (type is EndpointType.AzureOpenAI)
         {
             // Create a client that targets Azure OpenAI service or Azure API Management service.
             var clientOptions = new AzureOpenAIClientOptions() { RetryPolicy = new ChatRetryPolicy() };
@@ -152,6 +153,11 @@ private void RefreshOpenAIClient()
         {
             // Create a client that targets the non-Azure OpenAI service.
             var clientOptions = new OpenAIClientOptions() { RetryPolicy = new ChatRetryPolicy() };
+            if (type is EndpointType.CompatibleThirdParty)
+            {
+                clientOptions.Endpoint = new(_gptToUse.Endpoint);
+            }
+
             var aiClient = new OpenAIClient(new ApiKeyCredential(userKey), clientOptions);
             _client = aiClient.GetChatClient(_gptToUse.ModelName);
         }