diff --git a/specification/storage/Microsoft.BlobStorage/models.tsp b/specification/storage/Microsoft.BlobStorage/models.tsp
index 267a74622cda..2ff205b9b620 100644
--- a/specification/storage/Microsoft.BlobStorage/models.tsp
+++ b/specification/storage/Microsoft.BlobStorage/models.tsp
@@ -2008,6 +2008,22 @@ alias EncryptionKeyParameter = {
   encryptionKey?: string;
 };
 
+alias AccessTierIfModifiedSinceParameter = {
+  /** Specify this header value to operate only on a blob if the access-tier has been modified since the specified date/time. */
+  @added(Versions.v2026_04_06)
+  @header("x-ms-access-tier-if-modified-since")
+  @encode("rfc7231")
+  accessTierIfModifiedSince?: utcDateTime;
+};
+
+alias AccessTierIfUnmodifiedSinceParameter = {
+  /** Specify this header value to operate only on a blob if the access-tier has not been modified since the specified date/time. */
+  @added(Versions.v2026_04_06)
+  @header("x-ms-access-tier-if-unmodified-since")
+  @encode("rfc7231")
+  accessTierIfUnmodifiedSince?: utcDateTime;
+};
+
 /** The If-Tags parameters. */
 alias IfTagsParameter = {
   /** Specify a SQL where clause on blob tags to operate only on blobs with a matching value. */
diff --git a/specification/storage/Microsoft.BlobStorage/routes.tsp b/specification/storage/Microsoft.BlobStorage/routes.tsp
index 6a1f7b1e8180..4438848f05ea 100644
--- a/specification/storage/Microsoft.BlobStorage/routes.tsp
+++ b/specification/storage/Microsoft.BlobStorage/routes.tsp
@@ -915,6 +915,9 @@ namespace Storage.Blob {
           @query
           @clientName("blobDeleteType")
           deletetype?: BlobDeleteType;
+
+          ...AccessTierIfModifiedSinceParameter;
+          ...AccessTierIfUnmodifiedSinceParameter;
         },
         {
           @statusCode statusCode: 202;
diff --git a/specification/storage/data-plane/Microsoft.BlobStorage/stable/2026-04-06/generated_blob.json b/specification/storage/data-plane/Microsoft.BlobStorage/stable/2026-04-06/generated_blob.json
index 2d435da760f5..af353f5a6d70 100644
--- a/specification/storage/data-plane/Microsoft.BlobStorage/stable/2026-04-06/generated_blob.json
+++ b/specification/storage/data-plane/Microsoft.BlobStorage/stable/2026-04-06/generated_blob.json
@@ -1599,6 +1599,24 @@
               ]
             },
             "x-ms-client-name": "blobDeleteType"
+          },
+          {
+            "name": "x-ms-access-tier-if-modified-since",
+            "in": "header",
+            "description": "Specify this header value to operate only on a blob if the access-tier has been modified since the specified date/time.",
+            "required": false,
+            "type": "string",
+            "format": "date-time-rfc7231",
+            "x-ms-client-name": "accessTierIfModifiedSince"
+          },
+          {
+            "name": "x-ms-access-tier-if-unmodified-since",
+            "in": "header",
+            "description": "Specify this header value to operate only on a blob if the access-tier has not been modified since the specified date/time.",
+            "required": false,
+            "type": "string",
+            "format": "date-time-rfc7231",
+            "x-ms-client-name": "accessTierIfUnmodifiedSince"
           }
         ],
         "responses": {