diff --git a/CHANGELOG.md b/CHANGELOG.md
index ad396cd2e..6a9e6539c 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -6,6 +6,9 @@ Format based on [Keep a Changelog](https://keepachangelog.com/).
 
 ## [Unreleased]
 
+### Added
+- Sprint 13 "Sound" briefings — 9 tickets across server, client, audio, visual teams; full audio architecture + gauntlet expansion + monologue display spec
+
 ### Fixed
 - Routine tests missing ActiveSim — 3 of 5 tests passed trivially without the required tier marker
 - `_observer_pos` misleading unused prefix renamed to `observer_pos` (used for sound event filtering)