diff --git a/api/v3/api_proto/issue_objects.proto b/api/v3/api_proto/issue_objects.proto
index 790ea4b..b866cea 100644
--- a/api/v3/api_proto/issue_objects.proto
+++ b/api/v3/api_proto/issue_objects.proto
@@ -1,7 +1,6 @@
-// Copyright 2020 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style
-// license that can be found in the LICENSE file or at
-// https://developers.google.com/open-source/licenses/bsd
+// Copyright 2020 The Chromium Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
 
 // This file defines protobufs for issues and related business
 // objects, e.g., field values, comments, and attachments.
@@ -146,7 +145,7 @@
 }
 
 // Documents and tracks a bug, task, or feature request within a Project.
-// Next available tag: 23
+// Next available tag: 24
 message Issue {
   option (google.api.resource) = {
     type: "api.crbug.com/Issue"
@@ -253,6 +252,8 @@
   // See monorail/doc/userguide/concepts.md#issue-approvals-and-gates
   repeated string phases = 22 [
       (google.api.field_behavior) = OUTPUT_ONLY];
+  // The issue tracker ID this Monorail issue migrated to.
+  string migrated_id = 23;
 }
 
 // States that an issue or its comments can be in (aip.dev/216).
@@ -346,4 +347,4 @@
       (google.api.field_behavior) = OUTPUT_ONLY];
   // FieldValues with `approval_def` as their parent.
   repeated FieldValue field_values = 8;
-}
\ No newline at end of file
+}