/errors/experiment_error.proto 

--- v23/errors/experiment_error.proto   2026-05-08 16:34:09.000000000 +0000
+++ v24/errors/experiment_error.proto   2026-05-08 16:34:18.000000000 +0000
@@ -136,5 +136,11 @@
     // The experiment's campaigns must self-declare whether they contain
     // political advertising that targets the European Union.
     MISSING_EU_POLITICAL_ADVERTISING_SELF_DECLARATION = 31;
+
+    // Cannot create an experiment with no arms.
+    MISSING_EXPERIMENT_ARMS = 32;
+
+    // The video experiment subtype is missing.
+    MISSING_VIDEO_EXPERIMENT_SUBTYPE = 34;
   }
 }