diff --git a/CHANGELOG.md b/CHANGELOG.md
index e0817055..9e44f3a6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,6 +1,14 @@
 Arduino JSON: change log
 ========================
 
+v4.0
+----
+
+* Unified parser and generator API (issue #23)
+
+**BREAKING CHANGE**: API changed significantly, see `doc/Migrating to the new API.md`.
+
+
 v3.4
 ----