diff --git a/packages/google-cloud-managedidentities/src/v1/managed_identities_service_client.ts b/packages/google-cloud-managedidentities/src/v1/managed_identities_service_client.ts
index 943b486c353..e3411aa2bd5 100644
--- a/packages/google-cloud-managedidentities/src/v1/managed_identities_service_client.ts
+++ b/packages/google-cloud-managedidentities/src/v1/managed_identities_service_client.ts
@@ -17,8 +17,8 @@
 // ** All changes to this file may be overwritten. **
 
 /* global window */
-import * as gax from 'google-gax';
-import {
+import type * as gax from 'google-gax';
+import type {
   Callback,
   CallOptions,
   Descriptors,
@@ -28,7 +28,6 @@ import {
   PaginationCallback,
   GaxCall,
 } from 'google-gax';
-
 import {Transform} from 'stream';
 import * as protos from '../../protos/protos';
 import jsonProtos = require('../../protos/protos.json');
@@ -38,7 +37,6 @@ import jsonProtos = require('../../protos/protos.json');
  * This file defines retry strategy and timeouts for all API methods in this library.
  */
 import * as gapicConfig from './managed_identities_service_client_config.json';
-import {operationsProtos} from 'google-gax';
 const version = require('../../../package.json').version;
 
 /**
@@ -130,8 +128,18 @@ export class ManagedIdentitiesServiceClient {
    *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
+   * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
+   *     need to avoid loading the default gRPC version and want to use the fallback
+   *     HTTP implementation. Load only fallback version and pass it to the constructor:
+   *     ```
+   *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
+   *     const client = new ManagedIdentitiesServiceClient({fallback: 'rest'}, gax);
+   *     ```
    */
-  constructor(opts?: ClientOptions) {
+  constructor(
+    opts?: ClientOptions,
+    gaxInstance?: typeof gax | typeof gax.fallback
+  ) {
     // Ensure that options include all the required fields.
     const staticMembers = this
       .constructor as typeof ManagedIdentitiesServiceClient;
@@ -152,8 +160,13 @@ export class ManagedIdentitiesServiceClient {
       opts['scopes'] = staticMembers.scopes;
     }
 
+    // Load google-gax module synchronously if needed
+    if (!gaxInstance) {
+      gaxInstance = require('google-gax') as typeof gax;
+    }
+
     // Choose either gRPC or proto-over-HTTP implementation of google-gax.
-    this._gaxModule = opts.fallback ? gax.fallback : gax;
+    this._gaxModule = opts.fallback ? gaxInstance.fallback : gaxInstance;
 
     // Create a `gaxGrpc` object, with any grpc-specific options sent to the client.
     this._gaxGrpc = new this._gaxModule.GrpcClient(opts);
@@ -401,7 +414,7 @@ export class ManagedIdentitiesServiceClient {
     this.innerApiCalls = {};
 
     // Add a warn function to the client constructor so it can be easily tested.
-    this.warn = gax.warn;
+    this.warn = this._gaxModule.warn;
   }
 
   /**
@@ -626,7 +639,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         name: request.name || '',
       });
     this.initialize();
@@ -718,7 +731,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         name: request.name || '',
       });
     this.initialize();
@@ -838,7 +851,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         parent: request.parent || '',
       });
     this.initialize();
@@ -868,11 +881,12 @@ export class ManagedIdentitiesServiceClient {
       protos.google.cloud.managedidentities.v1.OpMetadata
     >
   > {
-    const request = new operationsProtos.google.longrunning.GetOperationRequest(
-      {name}
-    );
+    const request =
+      new this._gaxModule.operationsProtos.google.longrunning.GetOperationRequest(
+        {name}
+      );
     const [operation] = await this.operationsClient.getOperation(request);
-    const decodeOperation = new gax.Operation(
+    const decodeOperation = new this._gaxModule.Operation(
       operation,
       this.descriptors.longrunning.createMicrosoftAdDomain,
       this._gaxModule.createDefaultBackoffSettings()
@@ -987,7 +1001,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         'domain.name': request.domain!.name || '',
       });
     this.initialize();
@@ -1013,11 +1027,12 @@ export class ManagedIdentitiesServiceClient {
       protos.google.cloud.managedidentities.v1.OpMetadata
     >
   > {
-    const request = new operationsProtos.google.longrunning.GetOperationRequest(
-      {name}
-    );
+    const request =
+      new this._gaxModule.operationsProtos.google.longrunning.GetOperationRequest(
+        {name}
+      );
     const [operation] = await this.operationsClient.getOperation(request);
-    const decodeOperation = new gax.Operation(
+    const decodeOperation = new this._gaxModule.Operation(
       operation,
       this.descriptors.longrunning.updateDomain,
       this._gaxModule.createDefaultBackoffSettings()
@@ -1125,7 +1140,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         name: request.name || '',
       });
     this.initialize();
@@ -1151,11 +1166,12 @@ export class ManagedIdentitiesServiceClient {
       protos.google.cloud.managedidentities.v1.OpMetadata
     >
   > {
-    const request = new operationsProtos.google.longrunning.GetOperationRequest(
-      {name}
-    );
+    const request =
+      new this._gaxModule.operationsProtos.google.longrunning.GetOperationRequest(
+        {name}
+      );
     const [operation] = await this.operationsClient.getOperation(request);
-    const decodeOperation = new gax.Operation(
+    const decodeOperation = new this._gaxModule.Operation(
       operation,
       this.descriptors.longrunning.deleteDomain,
       this._gaxModule.createDefaultBackoffSettings()
@@ -1265,7 +1281,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         name: request.name || '',
       });
     this.initialize();
@@ -1291,11 +1307,12 @@ export class ManagedIdentitiesServiceClient {
       protos.google.cloud.managedidentities.v1.OpMetadata
     >
   > {
-    const request = new operationsProtos.google.longrunning.GetOperationRequest(
-      {name}
-    );
+    const request =
+      new this._gaxModule.operationsProtos.google.longrunning.GetOperationRequest(
+        {name}
+      );
     const [operation] = await this.operationsClient.getOperation(request);
-    const decodeOperation = new gax.Operation(
+    const decodeOperation = new this._gaxModule.Operation(
       operation,
       this.descriptors.longrunning.attachTrust,
       this._gaxModule.createDefaultBackoffSettings()
@@ -1409,7 +1426,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         name: request.name || '',
       });
     this.initialize();
@@ -1435,11 +1452,12 @@ export class ManagedIdentitiesServiceClient {
       protos.google.cloud.managedidentities.v1.OpMetadata
     >
   > {
-    const request = new operationsProtos.google.longrunning.GetOperationRequest(
-      {name}
-    );
+    const request =
+      new this._gaxModule.operationsProtos.google.longrunning.GetOperationRequest(
+        {name}
+      );
     const [operation] = await this.operationsClient.getOperation(request);
-    const decodeOperation = new gax.Operation(
+    const decodeOperation = new this._gaxModule.Operation(
       operation,
       this.descriptors.longrunning.reconfigureTrust,
       this._gaxModule.createDefaultBackoffSettings()
@@ -1549,7 +1567,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         name: request.name || '',
       });
     this.initialize();
@@ -1575,11 +1593,12 @@ export class ManagedIdentitiesServiceClient {
       protos.google.cloud.managedidentities.v1.OpMetadata
     >
   > {
-    const request = new operationsProtos.google.longrunning.GetOperationRequest(
-      {name}
-    );
+    const request =
+      new this._gaxModule.operationsProtos.google.longrunning.GetOperationRequest(
+        {name}
+      );
     const [operation] = await this.operationsClient.getOperation(request);
-    const decodeOperation = new gax.Operation(
+    const decodeOperation = new this._gaxModule.Operation(
       operation,
       this.descriptors.longrunning.detachTrust,
       this._gaxModule.createDefaultBackoffSettings()
@@ -1690,7 +1709,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         name: request.name || '',
       });
     this.initialize();
@@ -1716,11 +1735,12 @@ export class ManagedIdentitiesServiceClient {
       protos.google.cloud.managedidentities.v1.OpMetadata
     >
   > {
-    const request = new operationsProtos.google.longrunning.GetOperationRequest(
-      {name}
-    );
+    const request =
+      new this._gaxModule.operationsProtos.google.longrunning.GetOperationRequest(
+        {name}
+      );
     const [operation] = await this.operationsClient.getOperation(request);
-    const decodeOperation = new gax.Operation(
+    const decodeOperation = new this._gaxModule.Operation(
       operation,
       this.descriptors.longrunning.validateTrust,
       this._gaxModule.createDefaultBackoffSettings()
@@ -1837,7 +1857,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         parent: request.parent || '',
       });
     this.initialize();
@@ -1890,7 +1910,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         parent: request.parent || '',
       });
     const defaultCallSettings = this._defaults['listDomains'];
@@ -1952,7 +1972,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         parent: request.parent || '',
       });
     const defaultCallSettings = this._defaults['listDomains'];
diff --git a/packages/google-cloud-managedidentities/src/v1beta1/managed_identities_service_client.ts b/packages/google-cloud-managedidentities/src/v1beta1/managed_identities_service_client.ts
index 86580383c84..0950457564a 100644
--- a/packages/google-cloud-managedidentities/src/v1beta1/managed_identities_service_client.ts
+++ b/packages/google-cloud-managedidentities/src/v1beta1/managed_identities_service_client.ts
@@ -17,8 +17,8 @@
 // ** All changes to this file may be overwritten. **
 
 /* global window */
-import * as gax from 'google-gax';
-import {
+import type * as gax from 'google-gax';
+import type {
   Callback,
   CallOptions,
   Descriptors,
@@ -28,7 +28,6 @@ import {
   PaginationCallback,
   GaxCall,
 } from 'google-gax';
-
 import {Transform} from 'stream';
 import * as protos from '../../protos/protos';
 import jsonProtos = require('../../protos/protos.json');
@@ -38,7 +37,6 @@ import jsonProtos = require('../../protos/protos.json');
  * This file defines retry strategy and timeouts for all API methods in this library.
  */
 import * as gapicConfig from './managed_identities_service_client_config.json';
-import {operationsProtos} from 'google-gax';
 const version = require('../../../package.json').version;
 
 /**
@@ -98,8 +96,18 @@ export class ManagedIdentitiesServiceClient {
    *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
+   * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
+   *     need to avoid loading the default gRPC version and want to use the fallback
+   *     HTTP implementation. Load only fallback version and pass it to the constructor:
+   *     ```
+   *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
+   *     const client = new ManagedIdentitiesServiceClient({fallback: 'rest'}, gax);
+   *     ```
    */
-  constructor(opts?: ClientOptions) {
+  constructor(
+    opts?: ClientOptions,
+    gaxInstance?: typeof gax | typeof gax.fallback
+  ) {
     // Ensure that options include all the required fields.
     const staticMembers = this
       .constructor as typeof ManagedIdentitiesServiceClient;
@@ -120,8 +128,13 @@ export class ManagedIdentitiesServiceClient {
       opts['scopes'] = staticMembers.scopes;
     }
 
+    // Load google-gax module synchronously if needed
+    if (!gaxInstance) {
+      gaxInstance = require('google-gax') as typeof gax;
+    }
+
     // Choose either gRPC or proto-over-HTTP implementation of google-gax.
-    this._gaxModule = opts.fallback ? gax.fallback : gax;
+    this._gaxModule = opts.fallback ? gaxInstance.fallback : gaxInstance;
 
     // Create a `gaxGrpc` object, with any grpc-specific options sent to the client.
     this._gaxGrpc = new this._gaxModule.GrpcClient(opts);
@@ -369,7 +382,7 @@ export class ManagedIdentitiesServiceClient {
     this.innerApiCalls = {};
 
     // Add a warn function to the client constructor so it can be easily tested.
-    this.warn = gax.warn;
+    this.warn = this._gaxModule.warn;
   }
 
   /**
@@ -594,7 +607,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         name: request.name || '',
       });
     this.initialize();
@@ -692,7 +705,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         name: request.name || '',
       });
     this.initialize();
@@ -810,7 +823,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         parent: request.parent || '',
       });
     this.initialize();
@@ -840,11 +853,12 @@ export class ManagedIdentitiesServiceClient {
       protos.google.cloud.managedidentities.v1beta1.OpMetadata
     >
   > {
-    const request = new operationsProtos.google.longrunning.GetOperationRequest(
-      {name}
-    );
+    const request =
+      new this._gaxModule.operationsProtos.google.longrunning.GetOperationRequest(
+        {name}
+      );
     const [operation] = await this.operationsClient.getOperation(request);
-    const decodeOperation = new gax.Operation(
+    const decodeOperation = new this._gaxModule.Operation(
       operation,
       this.descriptors.longrunning.createMicrosoftAdDomain,
       this._gaxModule.createDefaultBackoffSettings()
@@ -960,7 +974,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         'domain.name': request.domain!.name || '',
       });
     this.initialize();
@@ -986,11 +1000,12 @@ export class ManagedIdentitiesServiceClient {
       protos.google.cloud.managedidentities.v1beta1.OpMetadata
     >
   > {
-    const request = new operationsProtos.google.longrunning.GetOperationRequest(
-      {name}
-    );
+    const request =
+      new this._gaxModule.operationsProtos.google.longrunning.GetOperationRequest(
+        {name}
+      );
     const [operation] = await this.operationsClient.getOperation(request);
-    const decodeOperation = new gax.Operation(
+    const decodeOperation = new this._gaxModule.Operation(
       operation,
       this.descriptors.longrunning.updateDomain,
       this._gaxModule.createDefaultBackoffSettings()
@@ -1098,7 +1113,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         name: request.name || '',
       });
     this.initialize();
@@ -1124,11 +1139,12 @@ export class ManagedIdentitiesServiceClient {
       protos.google.cloud.managedidentities.v1beta1.OpMetadata
     >
   > {
-    const request = new operationsProtos.google.longrunning.GetOperationRequest(
-      {name}
-    );
+    const request =
+      new this._gaxModule.operationsProtos.google.longrunning.GetOperationRequest(
+        {name}
+      );
     const [operation] = await this.operationsClient.getOperation(request);
-    const decodeOperation = new gax.Operation(
+    const decodeOperation = new this._gaxModule.Operation(
       operation,
       this.descriptors.longrunning.deleteDomain,
       this._gaxModule.createDefaultBackoffSettings()
@@ -1238,7 +1254,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         name: request.name || '',
       });
     this.initialize();
@@ -1264,11 +1280,12 @@ export class ManagedIdentitiesServiceClient {
       protos.google.cloud.managedidentities.v1beta1.OpMetadata
     >
   > {
-    const request = new operationsProtos.google.longrunning.GetOperationRequest(
-      {name}
-    );
+    const request =
+      new this._gaxModule.operationsProtos.google.longrunning.GetOperationRequest(
+        {name}
+      );
     const [operation] = await this.operationsClient.getOperation(request);
-    const decodeOperation = new gax.Operation(
+    const decodeOperation = new this._gaxModule.Operation(
       operation,
       this.descriptors.longrunning.attachTrust,
       this._gaxModule.createDefaultBackoffSettings()
@@ -1382,7 +1399,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         name: request.name || '',
       });
     this.initialize();
@@ -1408,11 +1425,12 @@ export class ManagedIdentitiesServiceClient {
       protos.google.cloud.managedidentities.v1beta1.OpMetadata
     >
   > {
-    const request = new operationsProtos.google.longrunning.GetOperationRequest(
-      {name}
-    );
+    const request =
+      new this._gaxModule.operationsProtos.google.longrunning.GetOperationRequest(
+        {name}
+      );
     const [operation] = await this.operationsClient.getOperation(request);
-    const decodeOperation = new gax.Operation(
+    const decodeOperation = new this._gaxModule.Operation(
       operation,
       this.descriptors.longrunning.reconfigureTrust,
       this._gaxModule.createDefaultBackoffSettings()
@@ -1522,7 +1540,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         name: request.name || '',
       });
     this.initialize();
@@ -1548,11 +1566,12 @@ export class ManagedIdentitiesServiceClient {
       protos.google.cloud.managedidentities.v1beta1.OpMetadata
     >
   > {
-    const request = new operationsProtos.google.longrunning.GetOperationRequest(
-      {name}
-    );
+    const request =
+      new this._gaxModule.operationsProtos.google.longrunning.GetOperationRequest(
+        {name}
+      );
     const [operation] = await this.operationsClient.getOperation(request);
-    const decodeOperation = new gax.Operation(
+    const decodeOperation = new this._gaxModule.Operation(
       operation,
       this.descriptors.longrunning.detachTrust,
       this._gaxModule.createDefaultBackoffSettings()
@@ -1663,7 +1682,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         name: request.name || '',
       });
     this.initialize();
@@ -1689,11 +1708,12 @@ export class ManagedIdentitiesServiceClient {
       protos.google.cloud.managedidentities.v1beta1.OpMetadata
     >
   > {
-    const request = new operationsProtos.google.longrunning.GetOperationRequest(
-      {name}
-    );
+    const request =
+      new this._gaxModule.operationsProtos.google.longrunning.GetOperationRequest(
+        {name}
+      );
     const [operation] = await this.operationsClient.getOperation(request);
-    const decodeOperation = new gax.Operation(
+    const decodeOperation = new this._gaxModule.Operation(
       operation,
       this.descriptors.longrunning.validateTrust,
       this._gaxModule.createDefaultBackoffSettings()
@@ -1810,7 +1830,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         parent: request.parent || '',
       });
     this.initialize();
@@ -1863,7 +1883,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         parent: request.parent || '',
       });
     const defaultCallSettings = this._defaults['listDomains'];
@@ -1925,7 +1945,7 @@ export class ManagedIdentitiesServiceClient {
     options.otherArgs = options.otherArgs || {};
     options.otherArgs.headers = options.otherArgs.headers || {};
     options.otherArgs.headers['x-goog-request-params'] =
-      gax.routingHeader.fromParams({
+      this._gaxModule.routingHeader.fromParams({
         parent: request.parent || '',
       });
     const defaultCallSettings = this._defaults['listDomains'];