diff --git a/src/v3/folders_client.ts b/src/v3/folders_client.ts
index 0c4e779..36155cc 100644
--- a/src/v3/folders_client.ts
+++ b/src/v3/folders_client.ts
@@ -23,6 +23,7 @@ import {
   CallOptions,
   Descriptors,
   ClientOptions,
+  GrpcClientOptions,
   LROperation,
   PaginationCallback,
   GaxCall,
@@ -74,7 +75,7 @@ export class FoldersClient {
    *
    * @param {object} [options] - The configuration object.
    * The options accepted by the constructor are described in detail
-   * in [this document](https://github.com/googleapis/gax-nodejs/blob/master/client-libraries.md#creating-the-client-instance).
+   * in [this document](https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#creating-the-client-instance).
    * The common options are:
    * @param {object} [options.credentials] - Credentials object.
    * @param {string} [options.credentials.client_email]
@@ -97,11 +98,10 @@ export class FoldersClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean} [options.fallback] - Use HTTP fallback mode.
-   *     In fallback mode, a special browser-compatible transport implementation is used
-   *     instead of gRPC transport. In browser context (if the `window` object is defined)
-   *     the fallback mode is enabled automatically; set `options.fallback` to `false`
-   *     if you need to override this behavior.
+   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
+   *     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}.
    */
   constructor(opts?: ClientOptions) {
     // Ensure that options include all the required fields.
@@ -201,16 +201,24 @@ export class FoldersClient {
     };
 
     const protoFilesRoot = this._gaxModule.protobuf.Root.fromJSON(jsonProtos);
-
     // This API contains "long-running operations", which return a
     // an Operation object that allows for tracking of the operation,
     // rather than holding a request open.
-
+    const lroOptions: GrpcClientOptions = {
+      auth: this.auth,
+      grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
+    };
+    if (opts.fallback === 'rest') {
+      lroOptions.protoJson = protoFilesRoot;
+      lroOptions.httpRules = [
+        {
+          selector: 'google.longrunning.Operations.GetOperation',
+          get: '/v3/{name=operations/**}',
+        },
+      ];
+    }
     this.operationsClient = this._gaxModule
-      .lro({
-        auth: this.auth,
-        grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
-      })
+      .lro(lroOptions)
       .operationsClient(opts);
     const createFolderResponse = protoFilesRoot.lookup(
       '.google.cloud.resourcemanager.v3.Folder'
diff --git a/src/v3/organizations_client.ts b/src/v3/organizations_client.ts
index c1fb430..5bde9b2 100644
--- a/src/v3/organizations_client.ts
+++ b/src/v3/organizations_client.ts
@@ -70,7 +70,7 @@ export class OrganizationsClient {
    *
    * @param {object} [options] - The configuration object.
    * The options accepted by the constructor are described in detail
-   * in [this document](https://github.com/googleapis/gax-nodejs/blob/master/client-libraries.md#creating-the-client-instance).
+   * in [this document](https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#creating-the-client-instance).
    * The common options are:
    * @param {object} [options.credentials] - Credentials object.
    * @param {string} [options.credentials.client_email]
@@ -93,11 +93,10 @@ export class OrganizationsClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean} [options.fallback] - Use HTTP fallback mode.
-   *     In fallback mode, a special browser-compatible transport implementation is used
-   *     instead of gRPC transport. In browser context (if the `window` object is defined)
-   *     the fallback mode is enabled automatically; set `options.fallback` to `false`
-   *     if you need to override this behavior.
+   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
+   *     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}.
    */
   constructor(opts?: ClientOptions) {
     // Ensure that options include all the required fields.
diff --git a/src/v3/projects_client.ts b/src/v3/projects_client.ts
index 26d670a..e8f36e2 100644
--- a/src/v3/projects_client.ts
+++ b/src/v3/projects_client.ts
@@ -23,6 +23,7 @@ import {
   CallOptions,
   Descriptors,
   ClientOptions,
+  GrpcClientOptions,
   LROperation,
   PaginationCallback,
   GaxCall,
@@ -72,7 +73,7 @@ export class ProjectsClient {
    *
    * @param {object} [options] - The configuration object.
    * The options accepted by the constructor are described in detail
-   * in [this document](https://github.com/googleapis/gax-nodejs/blob/master/client-libraries.md#creating-the-client-instance).
+   * in [this document](https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#creating-the-client-instance).
    * The common options are:
    * @param {object} [options.credentials] - Credentials object.
    * @param {string} [options.credentials.client_email]
@@ -95,11 +96,10 @@ export class ProjectsClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean} [options.fallback] - Use HTTP fallback mode.
-   *     In fallback mode, a special browser-compatible transport implementation is used
-   *     instead of gRPC transport. In browser context (if the `window` object is defined)
-   *     the fallback mode is enabled automatically; set `options.fallback` to `false`
-   *     if you need to override this behavior.
+   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
+   *     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}.
    */
   constructor(opts?: ClientOptions) {
     // Ensure that options include all the required fields.
@@ -199,16 +199,24 @@ export class ProjectsClient {
     };
 
     const protoFilesRoot = this._gaxModule.protobuf.Root.fromJSON(jsonProtos);
-
     // This API contains "long-running operations", which return a
     // an Operation object that allows for tracking of the operation,
     // rather than holding a request open.
-
+    const lroOptions: GrpcClientOptions = {
+      auth: this.auth,
+      grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
+    };
+    if (opts.fallback === 'rest') {
+      lroOptions.protoJson = protoFilesRoot;
+      lroOptions.httpRules = [
+        {
+          selector: 'google.longrunning.Operations.GetOperation',
+          get: '/v3/{name=operations/**}',
+        },
+      ];
+    }
     this.operationsClient = this._gaxModule
-      .lro({
-        auth: this.auth,
-        grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
-      })
+      .lro(lroOptions)
       .operationsClient(opts);
     const createProjectResponse = protoFilesRoot.lookup(
       '.google.cloud.resourcemanager.v3.Project'
diff --git a/src/v3/tag_bindings_client.ts b/src/v3/tag_bindings_client.ts
index d039a63..76bed17 100644
--- a/src/v3/tag_bindings_client.ts
+++ b/src/v3/tag_bindings_client.ts
@@ -23,6 +23,7 @@ import {
   CallOptions,
   Descriptors,
   ClientOptions,
+  GrpcClientOptions,
   LROperation,
   PaginationCallback,
   GaxCall,
@@ -73,7 +74,7 @@ export class TagBindingsClient {
    *
    * @param {object} [options] - The configuration object.
    * The options accepted by the constructor are described in detail
-   * in [this document](https://github.com/googleapis/gax-nodejs/blob/master/client-libraries.md#creating-the-client-instance).
+   * in [this document](https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#creating-the-client-instance).
    * The common options are:
    * @param {object} [options.credentials] - Credentials object.
    * @param {string} [options.credentials.client_email]
@@ -96,11 +97,10 @@ export class TagBindingsClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean} [options.fallback] - Use HTTP fallback mode.
-   *     In fallback mode, a special browser-compatible transport implementation is used
-   *     instead of gRPC transport. In browser context (if the `window` object is defined)
-   *     the fallback mode is enabled automatically; set `options.fallback` to `false`
-   *     if you need to override this behavior.
+   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
+   *     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}.
    */
   constructor(opts?: ClientOptions) {
     // Ensure that options include all the required fields.
@@ -195,16 +195,24 @@ export class TagBindingsClient {
     };
 
     const protoFilesRoot = this._gaxModule.protobuf.Root.fromJSON(jsonProtos);
-
     // This API contains "long-running operations", which return a
     // an Operation object that allows for tracking of the operation,
     // rather than holding a request open.
-
+    const lroOptions: GrpcClientOptions = {
+      auth: this.auth,
+      grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
+    };
+    if (opts.fallback === 'rest') {
+      lroOptions.protoJson = protoFilesRoot;
+      lroOptions.httpRules = [
+        {
+          selector: 'google.longrunning.Operations.GetOperation',
+          get: '/v3/{name=operations/**}',
+        },
+      ];
+    }
     this.operationsClient = this._gaxModule
-      .lro({
-        auth: this.auth,
-        grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
-      })
+      .lro(lroOptions)
       .operationsClient(opts);
     const createTagBindingResponse = protoFilesRoot.lookup(
       '.google.cloud.resourcemanager.v3.TagBinding'
diff --git a/src/v3/tag_keys_client.ts b/src/v3/tag_keys_client.ts
index 5267433..2606a54 100644
--- a/src/v3/tag_keys_client.ts
+++ b/src/v3/tag_keys_client.ts
@@ -23,6 +23,7 @@ import {
   CallOptions,
   Descriptors,
   ClientOptions,
+  GrpcClientOptions,
   LROperation,
   PaginationCallback,
   GaxCall,
@@ -72,7 +73,7 @@ export class TagKeysClient {
    *
    * @param {object} [options] - The configuration object.
    * The options accepted by the constructor are described in detail
-   * in [this document](https://github.com/googleapis/gax-nodejs/blob/master/client-libraries.md#creating-the-client-instance).
+   * in [this document](https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#creating-the-client-instance).
    * The common options are:
    * @param {object} [options.credentials] - Credentials object.
    * @param {string} [options.credentials.client_email]
@@ -95,11 +96,10 @@ export class TagKeysClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean} [options.fallback] - Use HTTP fallback mode.
-   *     In fallback mode, a special browser-compatible transport implementation is used
-   *     instead of gRPC transport. In browser context (if the `window` object is defined)
-   *     the fallback mode is enabled automatically; set `options.fallback` to `false`
-   *     if you need to override this behavior.
+   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
+   *     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}.
    */
   constructor(opts?: ClientOptions) {
     // Ensure that options include all the required fields.
@@ -194,16 +194,24 @@ export class TagKeysClient {
     };
 
     const protoFilesRoot = this._gaxModule.protobuf.Root.fromJSON(jsonProtos);
-
     // This API contains "long-running operations", which return a
     // an Operation object that allows for tracking of the operation,
     // rather than holding a request open.
-
+    const lroOptions: GrpcClientOptions = {
+      auth: this.auth,
+      grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
+    };
+    if (opts.fallback === 'rest') {
+      lroOptions.protoJson = protoFilesRoot;
+      lroOptions.httpRules = [
+        {
+          selector: 'google.longrunning.Operations.GetOperation',
+          get: '/v3/{name=operations/**}',
+        },
+      ];
+    }
     this.operationsClient = this._gaxModule
-      .lro({
-        auth: this.auth,
-        grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
-      })
+      .lro(lroOptions)
       .operationsClient(opts);
     const createTagKeyResponse = protoFilesRoot.lookup(
       '.google.cloud.resourcemanager.v3.TagKey'
diff --git a/src/v3/tag_values_client.ts b/src/v3/tag_values_client.ts
index d0c7c66..a9c2add 100644
--- a/src/v3/tag_values_client.ts
+++ b/src/v3/tag_values_client.ts
@@ -23,6 +23,7 @@ import {
   CallOptions,
   Descriptors,
   ClientOptions,
+  GrpcClientOptions,
   LROperation,
   PaginationCallback,
   GaxCall,
@@ -72,7 +73,7 @@ export class TagValuesClient {
    *
    * @param {object} [options] - The configuration object.
    * The options accepted by the constructor are described in detail
-   * in [this document](https://github.com/googleapis/gax-nodejs/blob/master/client-libraries.md#creating-the-client-instance).
+   * in [this document](https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#creating-the-client-instance).
    * The common options are:
    * @param {object} [options.credentials] - Credentials object.
    * @param {string} [options.credentials.client_email]
@@ -95,11 +96,10 @@ export class TagValuesClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean} [options.fallback] - Use HTTP fallback mode.
-   *     In fallback mode, a special browser-compatible transport implementation is used
-   *     instead of gRPC transport. In browser context (if the `window` object is defined)
-   *     the fallback mode is enabled automatically; set `options.fallback` to `false`
-   *     if you need to override this behavior.
+   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
+   *     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}.
    */
   constructor(opts?: ClientOptions) {
     // Ensure that options include all the required fields.
@@ -194,16 +194,24 @@ export class TagValuesClient {
     };
 
     const protoFilesRoot = this._gaxModule.protobuf.Root.fromJSON(jsonProtos);
-
     // This API contains "long-running operations", which return a
     // an Operation object that allows for tracking of the operation,
     // rather than holding a request open.
-
+    const lroOptions: GrpcClientOptions = {
+      auth: this.auth,
+      grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
+    };
+    if (opts.fallback === 'rest') {
+      lroOptions.protoJson = protoFilesRoot;
+      lroOptions.httpRules = [
+        {
+          selector: 'google.longrunning.Operations.GetOperation',
+          get: '/v3/{name=operations/**}',
+        },
+      ];
+    }
     this.operationsClient = this._gaxModule
-      .lro({
-        auth: this.auth,
-        grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
-      })
+      .lro(lroOptions)
       .operationsClient(opts);
     const createTagValueResponse = protoFilesRoot.lookup(
       '.google.cloud.resourcemanager.v3.TagValue'