diff --git a/google/cloud/bigquery/storage/v1alpha2/storage.proto b/google/cloud/bigquery/storage/v1alpha2/storage.proto
index e9a893b9..431f925b 100644
--- a/google/cloud/bigquery/storage/v1alpha2/storage.proto
+++ b/google/cloud/bigquery/storage/v1alpha2/storage.proto
@@ -169,6 +169,11 @@ message AppendRowsRequest {
   oneof rows {
     ProtoData proto_rows = 4;
   }
+
+  // Only initial request setting is respected. If true, drop unknown input
+  // fields. Otherwise, the extra fields will cause append to fail. Default
+  // value is false.
+  bool ignore_unknown_fields = 5;
 }
 
 // Response message for `AppendRows`.
@@ -181,6 +186,11 @@ message AppendRowsResponse {
     // into the system. Users can retry within the same connection.
     google.rpc.Status error = 2;
   }
+
+  // If backend detects a schema update, pass it to user so that user can
+  // use it to input new type of message. It will be empty when there is no
+  // schema updates.
+  TableSchema updated_schema = 3;
 }
 
 // Request message for `GetWriteStreamRequest`.