diff --git a/src/Libraries/Microsoft.Extensions.AI.Abstractions/CHANGELOG.md b/src/Libraries/Microsoft.Extensions.AI.Abstractions/CHANGELOG.md
index 4bb67980439..cc911fd64bb 100644
--- a/src/Libraries/Microsoft.Extensions.AI.Abstractions/CHANGELOG.md
+++ b/src/Libraries/Microsoft.Extensions.AI.Abstractions/CHANGELOG.md
@@ -3,6 +3,7 @@
 ## NOT YET RELEASED
 
 - Added new `ChatResponseFormat.ForJsonSchema` overloads that export a JSON schema from a .NET type.
+- Updated `TextReasoningContent` to include `ProtectedData` for representing encrypted/redacted content.
 
 ## 9.9.0
 
diff --git a/src/Libraries/Microsoft.Extensions.AI.Abstractions/ChatCompletion/ChatResponseExtensions.cs b/src/Libraries/Microsoft.Extensions.AI.Abstractions/ChatCompletion/ChatResponseExtensions.cs
index b9909857be2..933c6412c20 100644
--- a/src/Libraries/Microsoft.Extensions.AI.Abstractions/ChatCompletion/ChatResponseExtensions.cs
+++ b/src/Libraries/Microsoft.Extensions.AI.Abstractions/ChatCompletion/ChatResponseExtensions.cs
@@ -186,17 +186,17 @@ static async Task<ChatResponse> ToChatResponseAsync(
     /// <summary>Coalesces sequential <see cref="AIContent"/> content elements.</summary>
     internal static void CoalesceTextContent(IList<AIContent> contents)
     {
-        Coalesce<TextContent>(contents, mergeSingle: false, static (contents, start, end) =>
-            new(MergeText(contents, start, end))
-            {
-                AdditionalProperties = contents[start].AdditionalProperties?.Clone()
-            });
-
-        Coalesce<TextReasoningContent>(contents, mergeSingle: false, static (contents, start, end) =>
-            new(MergeText(contents, start, end))
-            {
-                AdditionalProperties = contents[start].AdditionalProperties?.Clone()
-            });
+        Coalesce<TextContent>(
+            contents,
+            mergeSingle: false,
+            canMerge: null,
+            static (contents, start, end) => new(MergeText(contents, start, end)) { AdditionalProperties = contents[start].AdditionalProperties?.Clone() });
+
+        Coalesce<TextReasoningContent>(
+            contents,
+            mergeSingle: false,
+            canMerge: static (r1, r2) => string.IsNullOrEmpty(r1.ProtectedData), // we allow merging if the first item has no ProtectedData, even if the second does
+            static (contents, start, end) => new(MergeText(contents, start, end)) { AdditionalProperties = contents[start].AdditionalProperties?.Clone() });
 
         static string MergeText(IList<AIContent> contents, int start, int end)
         {
@@ -209,7 +209,11 @@ static string MergeText(IList<AIContent> contents, int start, int end)
             return sb.ToString();
         }
 
-        static void Coalesce<TContent>(IList<AIContent> contents, bool mergeSingle, Func<IList<AIContent>, int, int, TContent> merge)
+        static void Coalesce<TContent>(
+            IList<AIContent> contents,
+            bool mergeSingle,
+            Func<TContent, TContent, bool>? canMerge,
+            Func<IList<AIContent>, int, int, TContent> merge)
             where TContent : AIContent
         {
             // Iterate through all of the items in the list looking for contiguous items that can be coalesced.
@@ -224,9 +228,11 @@ static void Coalesce<TContent>(IList<AIContent> contents, bool mergeSingle, Func
 
                 // Iterate until we find a non-coalescable item.
                 int i = start + 1;
-                while (i < contents.Count && TryAsCoalescable(contents[i], out _))
+                TContent prev = firstContent;
+                while (i < contents.Count && TryAsCoalescable(contents[i], out TContent? next) && (canMerge is null || canMerge(prev, next)))
                 {
                     i++;
+                    prev = next;
                 }
 
                 // If there's only one item in the run, and we don't want to merge single items, skip it.
diff --git a/src/Libraries/Microsoft.Extensions.AI.Abstractions/Contents/TextReasoningContent.cs b/src/Libraries/Microsoft.Extensions.AI.Abstractions/Contents/TextReasoningContent.cs
index ccf84af2e3d..345cb430dbd 100644
--- a/src/Libraries/Microsoft.Extensions.AI.Abstractions/Contents/TextReasoningContent.cs
+++ b/src/Libraries/Microsoft.Extensions.AI.Abstractions/Contents/TextReasoningContent.cs
@@ -38,6 +38,22 @@ public string Text
         set => _text = value;
     }
 
+    /// <summary>Gets or sets an optional opaque blob of data associated with this reasoning content.</summary>
+    /// <remarks>
+    /// <para>
+    /// This property is used to store data from a provider that should be roundtripped back to the provider but that is not
+    /// intended for human consumption. It is often encrypted or otherwise redacted information that is only intended to be
+    /// sent back to the provider and not displayed to the user. It's possible for a <see cref="TextReasoningContent"/> to contain
+    /// only <see cref="ProtectedData"/> and have an empty <see cref="Text"/> property. This data also may be associated with
+    /// the corresponding <see cref="Text"/>, acting as a validation signature for it.
+    /// </para>
+    /// <para>
+    /// Note that whereas <see cref="Text"/> can be provider agnostic, <see cref="ProtectedData"/>
+    /// is provider-specific, and is likely to only be understood by the provider that created it.
+    /// </para>
+    /// </remarks>
+    public string? ProtectedData { get; set; }
+
     /// <inheritdoc/>
     public override string ToString() => Text;
 
diff --git a/src/Libraries/Microsoft.Extensions.AI.Abstractions/Microsoft.Extensions.AI.Abstractions.json b/src/Libraries/Microsoft.Extensions.AI.Abstractions/Microsoft.Extensions.AI.Abstractions.json
index 034b5787eab..24239ee52b3 100644
--- a/src/Libraries/Microsoft.Extensions.AI.Abstractions/Microsoft.Extensions.AI.Abstractions.json
+++ b/src/Libraries/Microsoft.Extensions.AI.Abstractions/Microsoft.Extensions.AI.Abstractions.json
@@ -2430,6 +2430,10 @@
         {
           "Member": "string Microsoft.Extensions.AI.TextReasoningContent.Text { get; set; }",
           "Stage": "Stable"
+        },
+        {
+          "Member": "string? Microsoft.Extensions.AI.TextReasoningContent.ProtectedData { get; set; }",
+          "Stage": "Stable"
         }
       ]
     },
diff --git a/src/Libraries/Microsoft.Extensions.AI.OpenAI/OpenAIResponsesChatClient.cs b/src/Libraries/Microsoft.Extensions.AI.OpenAI/OpenAIResponsesChatClient.cs
index c025ae14d8a..0849b0c414f 100644
--- a/src/Libraries/Microsoft.Extensions.AI.OpenAI/OpenAIResponsesChatClient.cs
+++ b/src/Libraries/Microsoft.Extensions.AI.OpenAI/OpenAIResponsesChatClient.cs
@@ -17,6 +17,7 @@
 #pragma warning disable S907 // "goto" statement should not be used
 #pragma warning disable S1067 // Expressions should not be too complex
 #pragma warning disable S3011 // Reflection should not be used to increase accessibility of classes, methods, or fields
+#pragma warning disable S3254 // Default parameter values should not be passed as arguments
 #pragma warning disable S3604 // Member initializer values should not be redundant
 #pragma warning disable SA1202 // Elements should be ordered by access
 #pragma warning disable SA1204 // Static elements should appear before instance elements
@@ -149,8 +150,12 @@ internal static IEnumerable<ChatMessage> ToChatMessages(IEnumerable<ResponseItem
                     ((List<AIContent>)message.Contents).AddRange(ToAIContents(messageItem.Content));
                     break;
 
-                case ReasoningResponseItem reasoningItem when reasoningItem.GetSummaryText() is string summary:
-                    message.Contents.Add(new TextReasoningContent(summary) { RawRepresentation = outputItem });
+                case ReasoningResponseItem reasoningItem:
+                    message.Contents.Add(new TextReasoningContent(reasoningItem.GetSummaryText())
+                    {
+                        ProtectedData = reasoningItem.EncryptedContent,
+                        RawRepresentation = outputItem,
+                    });
                     break;
 
                 case FunctionCallResponseItem functionCall:
@@ -627,7 +632,9 @@ internal static IEnumerable<ResponseItem> ToOpenAIResponseItems(IEnumerable<Chat
                             break;
 
                         case TextReasoningContent reasoningContent:
-                            yield return ResponseItem.CreateReasoningItem(reasoningContent.Text);
+                            yield return OpenAIResponsesModelFactory.ReasoningResponseItem(
+                                encryptedContent: reasoningContent.ProtectedData,
+                                summaryText: reasoningContent.Text);
                             break;
 
                         case FunctionCallContent callContent:
diff --git a/test/Libraries/Microsoft.Extensions.AI.Abstractions.Tests/Contents/TextReasoningContentTests.cs b/test/Libraries/Microsoft.Extensions.AI.Abstractions.Tests/Contents/TextReasoningContentTests.cs
index 9d2e238a068..f64827e903b 100644
--- a/test/Libraries/Microsoft.Extensions.AI.Abstractions.Tests/Contents/TextReasoningContentTests.cs
+++ b/test/Libraries/Microsoft.Extensions.AI.Abstractions.Tests/Contents/TextReasoningContentTests.cs
@@ -16,6 +16,7 @@ public void Constructor_String_PropsDefault(string? text)
         TextReasoningContent c = new(text);
         Assert.Null(c.RawRepresentation);
         Assert.Null(c.AdditionalProperties);
+        Assert.Null(c.ProtectedData);
         Assert.Equal(text ?? string.Empty, c.Text);
     }
 
@@ -46,5 +47,11 @@ public void Constructor_PropsRoundtrip()
         c.Text = string.Empty;
         Assert.Equal(string.Empty, c.Text);
         Assert.Equal(string.Empty, c.ToString());
+
+        Assert.Null(c.ProtectedData);
+        c.ProtectedData = "protected";
+        Assert.Equal("protected", c.ProtectedData);
+        c.ProtectedData = null;
+        Assert.Null(c.ProtectedData);
     }
 }