diff --git a/src/Extensions/ReasoningEffort.cs b/src/Extensions/ReasoningEffort.cs
index 09c7cd9..8b7438c 100644
--- a/src/Extensions/ReasoningEffort.cs
+++ b/src/Extensions/ReasoningEffort.cs
@@ -1,4 +1,6 @@
-namespace Devlooped.Extensions.AI;
+using System.ComponentModel;
+
+namespace Devlooped.Extensions.AI;
 
 /// <summary>
 /// Effort a reasoning model should apply when generating a response.
@@ -12,7 +14,9 @@ public enum ReasoningEffort
     None,
     /// <summary>
     /// Minimal reasoning effort, which may result in faster responses. Support depends on the model.
+    /// Unsupported as of gpt-5.1+
     /// </summary>
+    [EditorBrowsable(EditorBrowsableState.Never)]
     Minimal,
     /// <summary>
     /// Low effort reasoning, which may result in faster responses but less detailed or accurate answers.
@@ -25,5 +29,9 @@ public enum ReasoningEffort
     /// <summary>
     /// High effort reasoning, which may take longer but provides more detailed and accurate responses.
     /// </summary>
-    High
+    High,
+    /// <summary>
+    /// New highest reasoning level as of gpt-5.2+.
+    /// </summary>
+    XHigh
 }
\ No newline at end of file
diff --git a/src/Tests/OpenAITests.cs b/src/Tests/OpenAITests.cs
index 9fd1880..c7985ac 100644
--- a/src/Tests/OpenAITests.cs
+++ b/src/Tests/OpenAITests.cs
@@ -121,12 +121,13 @@ public async Task GPT5_ThinksFast()
     }
 
     [SecretsTheory("OPENAI_API_KEY")]
+    [InlineData(ReasoningEffort.Minimal, "gpt-5")] // Obsolete as of 5.1
     [InlineData(ReasoningEffort.None)]
-    [InlineData(ReasoningEffort.Minimal)]
     [InlineData(ReasoningEffort.Low)]
     [InlineData(ReasoningEffort.Medium)]
     [InlineData(ReasoningEffort.High)]
-    public async Task GPT5_ThinkingTime(ReasoningEffort effort)
+    [InlineData(ReasoningEffort.XHigh)]
+    public async Task GPT5_ThinkingTime(ReasoningEffort effort, string modelId = "gpt-5.2")
     {
         var messages = new Chat()
         {
@@ -136,7 +137,7 @@ public async Task GPT5_ThinkingTime(ReasoningEffort effort)
 
         var requests = new List<JsonNode>();
 
-        var chat = new OpenAIChatClient(Configuration["OPENAI_API_KEY"]!, "gpt-5.2",
+        var chat = new OpenAIChatClient(Configuration["OPENAI_API_KEY"]!, modelId,
             OpenAIClientOptions.Observable(requests.Add).WriteTo(output));
 
         var options = new ChatOptions