diff --git a/protos/backend_service.proto b/protos/backend_service.proto
index b7cb601..5a8c62b 100644
--- a/protos/backend_service.proto
+++ b/protos/backend_service.proto
@@ -26,6 +26,9 @@ service BackendService {
     // and for sending orchestration lifecycle events, such as terminate, suspend, resume, etc.
     rpc AddEvent (AddEventRequest) returns (AddEventResponse);
 
+    // The same as the AddEvent API, except for sending events to multiple orchestration instances at once.
+    rpc AddEvents (AddEventsRequest) returns (AddEventsResponse);
+
     // Returns metadata about an orchestration instance.
     rpc GetInstance (GetInstanceRequest) returns (GetInstanceResponse);
 
@@ -101,6 +104,19 @@ message AddEventResponse {
     // No fields
 }
 
+// Request payload for adding new orchestration events to multiple instances.
+message AddEventsRequest {
+    // A map from instance IDs to the event to add to each.
+    map<string, HistoryEvent> events = 1;
+}
+
+// Response payload for adding new orchestration events to multiple instances.
+message AddEventsResponse {
+    // Those instances for which events were not successfully added.
+    // Events may not be successfully added due to capacity issues, or if the target instance does not exist.
+    repeated string unsuccessfulInstanceIds = 1;
+}
+
 // Request payload for waiting for instance completion.
 message WaitForInstanceRequest {
     string instanceId = 1;