diff --git a/changelog/3947.added.md b/changelog/3947.added.md
new file mode 100644
index 000000000..175cb87bd
--- /dev/null
+++ b/changelog/3947.added.md
@@ -0,0 +1 @@
+- Exposed `on_summary_applied` event on `LLMAssistantAggregator`, allowing users to listen for context summarization events without accessing private members.