diff --git a/RELEASE.md b/RELEASE.md
index ded22a7..6ab24e4 100644
--- a/RELEASE.md
+++ b/RELEASE.md
@@ -6,6 +6,7 @@ Features:
 
 - max_sum_2x2 including index of subcluster with highest energy is now available from Python API 
 - eta stores corner as enum class cTopLeft, cTopRight, BottomLeft, cBottomRight indicating 2x2 subcluster with largest energy relative to cluster center 
+- max_sum_2x2 returns corner as index
 
 ### 2025.10.1