diff --git a/google/home/graph/v1/homegraph.proto b/google/home/graph/v1/homegraph.proto
index 7edaf73f..37cba267 100644
--- a/google/home/graph/v1/homegraph.proto
+++ b/google/home/graph/v1/homegraph.proto
@@ -82,6 +82,11 @@ message RequestSyncDevicesRequest {
   // Required. Third-party user id issued by agent's third-party identity
   // provider.
   string agent_user_id = 1;
+
+  // Optional. If set, the request will be added to a queue and a response will
+  // be returned immediately. The queue allows for de-duplication of
+  // simultaneous requests.
+  bool async = 2;
 }
 
 // Response type for RequestSyncDevices call. Intentionally empty upon success.