diff --git a/CHANGELOG.md b/CHANGELOG.md
index c2027f29..df8ce2ed 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -3,6 +3,8 @@
 
 ## [Unreleased]
 
+## [v0.51.656] — 2026-06-25 — Release XL (stream writeback timing diagnostics)
+
 ### Fixed
 
 - **Final stream writeback now emits slow-stage diagnostics without changing the writeback contract.** Successful agent turns time the result merge, session save, persistent-state scan, optional `state.db` sync, and terminal `done` payload phases, logging a debug line only when the full writeback exceeds `HERMES_WEBUI_STREAM_WRITEBACK_DIAG_MS` (250 ms by default, negative disables). This gives the remaining #4918 lock-contention work a measured next step while preserving the existing active-stream lifecycle.