diff --git a/proto/src/metrics_constants.proto b/proto/src/metrics_constants.proto
index 8a3b9af..f06c8dcf 100644
--- a/proto/src/metrics_constants.proto
+++ b/proto/src/metrics_constants.proto
@@ -3777,6 +3777,9 @@
     // Package: Package of app that was autofilled
     AUTOFILL_SESSION_FINISHED = 919;
 
+    // meta-event: a reader has checkpointed the log here.
+    METRICS_CHECKPOINT = 920;
+
     // ---- End O Constants, all O constants go above this line ----
 
     // Add new aosp constants above this line.