diff --git a/sharing/proto/wire_format.proto b/sharing/proto/wire_format.proto
index 01f5a4d1..a3187cd5 100644
--- a/sharing/proto/wire_format.proto
+++ b/sharing/proto/wire_format.proto
@@ -233,6 +233,7 @@ message IntroductionFrame {
   repeated StreamMetadata stream_metadata = 7;
   optional SharingUseCase use_case = 8;
   repeated int64 preview_payload_ids = 9;
+  optional string transfer_id = 10;
 }
 
 // A progress update packet sent by the sending side. Contains transfer progress