diff --git a/docs/USAGE.md b/docs/USAGE.md
index 82586e49..d227d9d4 100644
--- a/docs/USAGE.md
+++ b/docs/USAGE.md
@@ -24,9 +24,32 @@ If you have any issues, questions or an idea for additional features, please tak
 ## Latest Changes
 
 ::: tip State of this document
-This documentation refers to release [v3.9.0](https://github.com/openhab/openhab-google-assistant/releases/tag/v3.9.0) of [openHAB Google Assistant](https://github.com/openhab/openhab-google-assistant) published on 2024-01-29
+This documentation refers to release [v4.0.0](https://github.com/openhab/openhab-google-assistant/releases/tag/v4.0.0) of [openHAB Google Assistant](https://github.com/openhab/openhab-google-assistant) published on 2024-05-31
 :::
 
+### v4.0.0
+
+- **Breaking Changes**
+  - Group members are now stored in customData. This means existing (group) devices will only work after a new SYNC
+  - The `modes` configuration for Thermostats has been renamed to `thermostatModes`
+  - The `speeds` configuration for Fans will be renamed to `fanSpeeds`
+  - As item types of group members will then be validated, users might see devices disappearing in Google Home if they used an unsupported item within a group device
+  - Please take a look at [Migration Guide](https://github.com/openhab/openhab-google-assistant/discussions/558) and check your configuration against the new constraints
+- **More details and other changes**
+  - Item names for group members will be stored in customData to save a query request to openHAB when executing commands
+    - For commands that need the current state the query request is still needed (thermostat commands or relative volume)
+    - Also some other configuration options are stored in customData
+    - Item types of group members will now be validated
+  - Add a lot of new functionality to Fan devices (AirPurifier, Fan, Hood)
+    - OnOff (separate power switch if used as a group)
+    - FanSpeed (separate fan speed if used as a group)
+    - Modes (yes, for the first time modes are available)
+    - SensorState (for FilterLifeTime and PM2.5 - no clue how to query those)
+  - Add AC Unit device
+    - Basically just a combination of the extended Fan and the Thermostat with all control and config options of both
+- **Potential Issues**
+  - As customData is limited to 512 bytes it could be an issue to store very long item names e.g. for devices with a lot of members like thermostat
+
 ### v3.9.0
 
 - Prepared available configuration options for the upcoming rollout of v4
diff --git a/functions/package-lock.json b/functions/package-lock.json
index 432b3d03..156f7b6d 100644
--- a/functions/package-lock.json
+++ b/functions/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "openhab.google-assistant-smarthome.cloud-function",
-  "version": "3.9.0",
+  "version": "4.0.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "openhab.google-assistant-smarthome.cloud-function",
-      "version": "3.9.0",
+      "version": "4.0.0",
       "license": "EPL-2.0",
       "dependencies": {
         "actions-on-google": "^3.0.0"
diff --git a/functions/package.json b/functions/package.json
index 7b1bb9c7..7f1d733b 100644
--- a/functions/package.json
+++ b/functions/package.json
@@ -1,6 +1,6 @@
 {
   "name": "openhab.google-assistant-smarthome.cloud-function",
-  "version": "3.9.0",
+  "version": "4.0.0",
   "description": "A Google Assistant, Actions on Google based implementation for openHAB",
   "repository": {
     "type": "git",
diff --git a/package-lock.json b/package-lock.json
index 810c3e97..58ac74b0 100644
--- a/package-lock.json
+++ b/package-lock.json
@@ -1,12 +1,12 @@
 {
   "name": "openhab.google-assistant-smarthome",
-  "version": "3.9.0",
+  "version": "4.0.0",
   "lockfileVersion": 3,
   "requires": true,
   "packages": {
     "": {
       "name": "openhab.google-assistant-smarthome",
-      "version": "3.9.0",
+      "version": "4.0.0",
       "license": "EPL-2.0",
       "dependencies": {
         "express": "^4.19.2"
diff --git a/package.json b/package.json
index bc897547..8e3249c9 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "openhab.google-assistant-smarthome",
-  "version": "3.9.0",
+  "version": "4.0.0",
   "description": "A Google Assistant, Actions on Google based implementation for openHAB",
   "main": "functions/index.js",
   "repository": {