diff --git a/src/logging/diagnostic-stability.ts b/src/logging/diagnostic-stability.ts
index affbdff6de0..0707b6d41d1 100644
--- a/src/logging/diagnostic-stability.ts
+++ b/src/logging/diagnostic-stability.ts
@@ -254,6 +254,7 @@ function sanitizeDiagnosticEvent(event: DiagnosticEventPayload): DiagnosticStabi
       record.bytes = event.promptChars;
       record.context =
         event.contextTokenBudget !== undefined ? { limit: event.contextTokenBudget } : undefined;
+      record.bytes = event.promptChars;
       break;
     case "diagnostic.heartbeat":
       record.webhooks = { ...event.webhooks };