diff --git a/sdk/subscription/arm-subscriptions/src/models/index.ts b/sdk/subscription/arm-subscriptions/src/models/index.ts
index 0b9eb62dcb39..56b1e85b1b45 100644
--- a/sdk/subscription/arm-subscriptions/src/models/index.ts
+++ b/sdk/subscription/arm-subscriptions/src/models/index.ts
@@ -160,6 +160,10 @@ export interface SubscriptionCreationParameters {
    * 'MS-AZR-0148P'
    */
   offerType?: OfferType;
+  /**
+   * Additional, untyped parameters to support custom subscription creation scenarios.
+   */
+  additionalParameters?: { [propertyName: string]: any };
 }
 
 /**
@@ -189,6 +193,10 @@ export interface ModernSubscriptionCreationParameters {
    * The identifier of the management group to which this subscription will be associated.
    */
   managementGroupId?: string;
+  /**
+   * Additional, untyped parameters to support custom subscription creation scenarios.
+   */
+  additionalParameters?: { [propertyName: string]: any };
 }
 
 /**
diff --git a/sdk/subscription/arm-subscriptions/src/models/mappers.ts b/sdk/subscription/arm-subscriptions/src/models/mappers.ts
index b753250be37a..6ce8d2762cbd 100644
--- a/sdk/subscription/arm-subscriptions/src/models/mappers.ts
+++ b/sdk/subscription/arm-subscriptions/src/models/mappers.ts
@@ -248,6 +248,17 @@ export const SubscriptionCreationParameters: msRest.CompositeMapper = {
         type: {
           name: "String"
         }
+      },
+      additionalParameters: {
+        serializedName: "additionalParameters",
+        type: {
+          name: "Dictionary",
+          value: {
+            type: {
+              name: "Object"
+            }
+          }
+        }
       }
     }
   }
@@ -291,6 +302,17 @@ export const ModernSubscriptionCreationParameters: msRest.CompositeMapper = {
         type: {
           name: "String"
         }
+      },
+      additionalParameters: {
+        serializedName: "additionalParameters",
+        type: {
+          name: "Dictionary",
+          value: {
+            type: {
+              name: "Object"
+            }
+          }
+        }
       }
     }
   }