diff --git a/specification/eventgrid/data-plane/Microsoft.Communication/stable/2018-01-01/AzureCommunicationServices.json b/specification/eventgrid/data-plane/Microsoft.Communication/stable/2018-01-01/AzureCommunicationServices.json
index 41a1140046ba..d352755c3a5e 100644
--- a/specification/eventgrid/data-plane/Microsoft.Communication/stable/2018-01-01/AzureCommunicationServices.json
+++ b/specification/eventgrid/data-plane/Microsoft.Communication/stable/2018-01-01/AzureCommunicationServices.json
@@ -18,6 +18,13 @@
         "messageBody": {
           "description": "The body of the chat message",
           "type": "string"
+        },
+        "metadata": {
+          "description": "The chat message metadata",
+          "type": "object",
+          "additionalProperties": {
+            "type": "string"
+          }
         }
       }
     },
@@ -32,6 +39,13 @@
         "messageBody": {
           "description": "The body of the chat message",
           "type": "string"
+        },
+        "metadata": {
+          "description": "The chat message metadata",
+          "type": "object",
+          "additionalProperties": {
+            "type": "string"
+          }
         }
       }
     },
@@ -47,6 +61,13 @@
           "description": "The body of the chat message",
           "type": "string"
         },
+        "metadata": {
+          "description": "The chat message metadata",
+          "type": "object",
+          "additionalProperties": {
+            "type": "string"
+          }
+        },
         "editTime": {
           "description": "The time at which the message was edited",
           "format": "date-time",
@@ -66,6 +87,13 @@
           "description": "The body of the chat message",
           "type": "string"
         },
+        "metadata": {
+          "description": "The chat message metadata",
+          "type": "object",
+          "additionalProperties": {
+            "type": "string"
+          }
+        },
         "editTime": {
           "description": "The time at which the message was edited",
           "format": "date-time",