Updated changelog.
diff --git a/CHANGES.txt b/CHANGES.txt
index d73ef27..14b9b3a 100644
--- a/CHANGES.txt
+++ b/CHANGES.txt
@@ -1,3 +1,18 @@
+Unreleased Changes (C++/Java/Python/PHP/Objective-C/C#/Ruby/JavaScript)
+
+ C++
+ * Allow MessageDifferencer::TreatAsSet() (and friends) to override previous
+ calls instead of crashing.
+ * Reduce the size of generated proto headers for protos with `string` or
+ `bytes` fields.
+ * Move arena() operation on uncommon path to out-of-line routine
+ * For iterator-pair function parameter types, take both iterators by value.
+ * Code-space savings and perhaps some modest performance improvements in
+ RepeatedPtrField.
+
+ Java:
+ * Exceptions thrown while reading from an InputStream in parseFrom are now included as causes.
+
2021-02-25 version 3.15.3 (C++/Java/Python/PHP/Objective-C/C#/Ruby/JavaScript)
Ruby
