/errors/experiment_error.proto 

--- v16/errors/experiment_error.proto   2024-04-18 17:10:01.000000000 +0000
+++ v16-1/errors/experiment_error.proto 2024-04-18 17:10:10.000000000 +0000
@@ -129,5 +129,8 @@
     // experiment types: SEARCH_CUSTOM, DISPLAY_CUSTOM,
     // DISPLAY_AUTOMATED_BIDDING_STRATEGY, SEARCH_AUTOMATED_BIDDING_STRATEGY.
     CANNOT_ENABLE_SYNC_FOR_UNSUPPORTED_EXPERIMENT_TYPE = 29;
+
+    // Experiment length cannot be longer than max length.
+    INVALID_DURATION_FOR_AN_EXPERIMENT = 30;
   }
 }