diff --git a/google/spanner/adapter/v1/adapter.proto b/google/spanner/adapter/v1/adapter.proto
index bc3afa35af..9c24e17799 100644
--- a/google/spanner/adapter/v1/adapter.proto
+++ b/google/spanner/adapter/v1/adapter.proto
@@ -92,6 +92,12 @@ message AdaptMessageResponse {
   // Optional. Opaque state updates to be applied by the client.
   map<string, string> state_updates = 2
       [(google.api.field_behavior) = OPTIONAL];
+
+  // Optional. Indicates whether this is the last
+  // [AdaptMessageResponse][google.spanner.adapter.v1.AdaptMessageResponse] in
+  // the stream. This field may be optionally set by the server. Clients should
+  // not rely on this field being set in all cases.
+  bool last = 3 [(google.api.field_behavior) = OPTIONAL];
 }
 
 // A session in the Cloud Spanner Adapter API.