diff --git a/CHANGELOG.md b/CHANGELOG.md
index 03d8ccf4..10f1c2df 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,9 +1,15 @@
 # Changelog
 
-## 22.0-SNAPSHOT - unreleased
+## 21.0.1 - 2024-09-05
+
+### 🐞 Bug Fixes
+
+* Resolved issue where connected clients would not display the upgrade prompt banner when an app was
+  first released with an update to `hoist-core >= 21.0.0`.
 
 ### ⚙️ Technical
-* Improvements to serialization efficiency of replicated `Cache` and `CachedValue`
+
+* Improved serialization efficiency of replicated `Cache` and `CachedValue`.
 
 ## 21.0.0 - 2024-09-03
 
diff --git a/grails-app/controllers/io/xh/hoist/impl/XhController.groovy b/grails-app/controllers/io/xh/hoist/impl/XhController.groovy
index 5822f875..d55c33db 100644
--- a/grails-app/controllers/io/xh/hoist/impl/XhController.groovy
+++ b/grails-app/controllers/io/xh/hoist/impl/XhController.groovy
@@ -285,7 +285,12 @@ class XhController extends BaseController {
             appVersion: Utils.appVersion,
             appBuild: Utils.appBuild,
             timestamp: System.currentTimeMillis(),
-            success: true
+            success: true,
+            // TODO - this is a temporary measure to ensure that clients running hoist-react < 67
+            //      prompt for upgrade when a new app release is deployed with hoist-core >= 21.
+            //      Going forward clients will read these instructions from `xh/environmentPoll`.
+            //      Once a majority of key apps have been upgraded, we should remove this key.
+            mode: configService.getMap('xhEnvPollConfig').onVersionChange
         )
     }