diff --git a/spec3.json b/spec3.json
index 1b7f759..2cf09bd 100644
--- a/spec3.json
+++ b/spec3.json
@@ -13889,6 +13889,19 @@
           "permission": {
             "$ref": "#/components/schemas/Permission"
           },
+          "createdById": {
+            "type": "string",
+            "description": "Identifier for the user who created this membership.",
+            "readOnly": true,
+            "format": "uuid",
+            "nullable": true
+          },
+          "createdAt": {
+            "type": "string",
+            "description": "The date and time that this membership was created.",
+            "readOnly": true,
+            "format": "date-time"
+          },
           "sourceId": {
             "type": "string",
             "description": "Identifier for the membership this one was inherited from, if any.",
diff --git a/spec3.yml b/spec3.yml
index fe6fbd6..9c54e74 100644
--- a/spec3.yml
+++ b/spec3.yml
@@ -9896,6 +9896,17 @@ components:
           nullable: true
         permission:
           "$ref": "#/components/schemas/Permission"
+        createdById:
+          type: string
+          description: Identifier for the user who created this membership.
+          readOnly: true
+          format: uuid
+          nullable: true
+        createdAt:
+          type: string
+          description: The date and time that this membership was created.
+          readOnly: true
+          format: date-time
         sourceId:
           type: string
           description: Identifier for the membership this one was inherited from, if any.