diff --git a/packages/google-cloud-networksecurity/samples/quickstart.js b/packages/google-cloud-networksecurity/samples/quickstart.js
index 878d4efdc6f..183929c5840 100644
--- a/packages/google-cloud-networksecurity/samples/quickstart.js
+++ b/packages/google-cloud-networksecurity/samples/quickstart.js
@@ -50,8 +50,9 @@ function main(parent) {
     };
 
     // Run request
-    const iterable =
-      await networksecurityClient.listClientTlsPoliciesAsync(request);
+    const iterable = await networksecurityClient.listClientTlsPoliciesAsync(
+      request
+    );
     for await (const response of iterable) {
       console.log(response);
     }
diff --git a/packages/google-cloud-networksecurity/src/v1/network_security_client.ts b/packages/google-cloud-networksecurity/src/v1/network_security_client.ts
index 76a20f84839..ae976508867 100644
--- a/packages/google-cloud-networksecurity/src/v1/network_security_client.ts
+++ b/packages/google-cloud-networksecurity/src/v1/network_security_client.ts
@@ -101,8 +101,7 @@ export class NetworkSecurityClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -110,7 +109,7 @@ export class NetworkSecurityClient {
    *     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 NetworkSecurityClient({fallback: 'rest'}, gax);
+   *     const client = new NetworkSecurityClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -182,7 +181,7 @@ export class NetworkSecurityClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -235,7 +234,7 @@ export class NetworkSecurityClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-networksecurity/src/v1beta1/network_security_client.ts b/packages/google-cloud-networksecurity/src/v1beta1/network_security_client.ts
index 99acea71eae..b263e53d42f 100644
--- a/packages/google-cloud-networksecurity/src/v1beta1/network_security_client.ts
+++ b/packages/google-cloud-networksecurity/src/v1beta1/network_security_client.ts
@@ -101,8 +101,7 @@ export class NetworkSecurityClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -110,7 +109,7 @@ export class NetworkSecurityClient {
    *     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 NetworkSecurityClient({fallback: 'rest'}, gax);
+   *     const client = new NetworkSecurityClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -182,7 +181,7 @@ export class NetworkSecurityClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -235,7 +234,7 @@ export class NetworkSecurityClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-notebooks/src/v1/managed_notebook_service_client.ts b/packages/google-cloud-notebooks/src/v1/managed_notebook_service_client.ts
index b3d1f2b613e..60d3a3a2c56 100644
--- a/packages/google-cloud-notebooks/src/v1/managed_notebook_service_client.ts
+++ b/packages/google-cloud-notebooks/src/v1/managed_notebook_service_client.ts
@@ -99,8 +99,7 @@ export class ManagedNotebookServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -108,7 +107,7 @@ export class ManagedNotebookServiceClient {
    *     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 ManagedNotebookServiceClient({fallback: 'rest'}, gax);
+   *     const client = new ManagedNotebookServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -181,7 +180,7 @@ export class ManagedNotebookServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -236,7 +235,7 @@ export class ManagedNotebookServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-notebooks/src/v1/notebook_service_client.ts b/packages/google-cloud-notebooks/src/v1/notebook_service_client.ts
index dc5c30946ed..233fdd7ddbd 100644
--- a/packages/google-cloud-notebooks/src/v1/notebook_service_client.ts
+++ b/packages/google-cloud-notebooks/src/v1/notebook_service_client.ts
@@ -99,8 +99,7 @@ export class NotebookServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -108,7 +107,7 @@ export class NotebookServiceClient {
    *     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 NotebookServiceClient({fallback: 'rest'}, gax);
+   *     const client = new NotebookServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -180,7 +179,7 @@ export class NotebookServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -244,7 +243,7 @@ export class NotebookServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-notebooks/src/v1beta1/notebook_service_client.ts b/packages/google-cloud-notebooks/src/v1beta1/notebook_service_client.ts
index ff877d97c9e..b01a4a50b00 100644
--- a/packages/google-cloud-notebooks/src/v1beta1/notebook_service_client.ts
+++ b/packages/google-cloud-notebooks/src/v1beta1/notebook_service_client.ts
@@ -99,8 +99,7 @@ export class NotebookServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -108,7 +107,7 @@ export class NotebookServiceClient {
    *     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 NotebookServiceClient({fallback: 'rest'}, gax);
+   *     const client = new NotebookServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -180,7 +179,7 @@ export class NotebookServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -225,7 +224,7 @@ export class NotebookServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-notebooks/src/v2/notebook_service_client.ts b/packages/google-cloud-notebooks/src/v2/notebook_service_client.ts
index 36c8d1b5616..72caae6ab56 100644
--- a/packages/google-cloud-notebooks/src/v2/notebook_service_client.ts
+++ b/packages/google-cloud-notebooks/src/v2/notebook_service_client.ts
@@ -99,8 +99,7 @@ export class NotebookServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -108,7 +107,7 @@ export class NotebookServiceClient {
    *     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 NotebookServiceClient({fallback: 'rest'}, gax);
+   *     const client = new NotebookServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -180,7 +179,7 @@ export class NotebookServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -223,7 +222,7 @@ export class NotebookServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-optimization/src/v1/fleet_routing_client.ts b/packages/google-cloud-optimization/src/v1/fleet_routing_client.ts
index 0f144dd07ac..3e783af1a08 100644
--- a/packages/google-cloud-optimization/src/v1/fleet_routing_client.ts
+++ b/packages/google-cloud-optimization/src/v1/fleet_routing_client.ts
@@ -106,8 +106,7 @@ export class FleetRoutingClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -115,7 +114,7 @@ export class FleetRoutingClient {
    *     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 FleetRoutingClient({fallback: 'rest'}, gax);
+   *     const client = new FleetRoutingClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -181,7 +180,7 @@ export class FleetRoutingClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -198,7 +197,7 @@ export class FleetRoutingClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-orchestration-airflow-service/src/v1/environments_client.ts b/packages/google-cloud-orchestration-airflow-service/src/v1/environments_client.ts
index aaac321e76c..2a8d210271a 100644
--- a/packages/google-cloud-orchestration-airflow-service/src/v1/environments_client.ts
+++ b/packages/google-cloud-orchestration-airflow-service/src/v1/environments_client.ts
@@ -93,8 +93,7 @@ export class EnvironmentsClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -102,7 +101,7 @@ export class EnvironmentsClient {
    *     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 EnvironmentsClient({fallback: 'rest'}, gax);
+   *     const client = new EnvironmentsClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -168,7 +167,7 @@ export class EnvironmentsClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -205,7 +204,7 @@ export class EnvironmentsClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-orchestration-airflow-service/src/v1/image_versions_client.ts b/packages/google-cloud-orchestration-airflow-service/src/v1/image_versions_client.ts
index a7c071825d1..f9b67725b6e 100644
--- a/packages/google-cloud-orchestration-airflow-service/src/v1/image_versions_client.ts
+++ b/packages/google-cloud-orchestration-airflow-service/src/v1/image_versions_client.ts
@@ -90,8 +90,7 @@ export class ImageVersionsClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -99,7 +98,7 @@ export class ImageVersionsClient {
    *     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 ImageVersionsClient({fallback: 'rest'}, gax);
+   *     const client = new ImageVersionsClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -165,7 +164,7 @@ export class ImageVersionsClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
diff --git a/packages/google-cloud-orchestration-airflow-service/src/v1beta1/environments_client.ts b/packages/google-cloud-orchestration-airflow-service/src/v1beta1/environments_client.ts
index d8b56b8d2b4..f54e6bf1d10 100644
--- a/packages/google-cloud-orchestration-airflow-service/src/v1beta1/environments_client.ts
+++ b/packages/google-cloud-orchestration-airflow-service/src/v1beta1/environments_client.ts
@@ -93,8 +93,7 @@ export class EnvironmentsClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -102,7 +101,7 @@ export class EnvironmentsClient {
    *     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 EnvironmentsClient({fallback: 'rest'}, gax);
+   *     const client = new EnvironmentsClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -168,7 +167,7 @@ export class EnvironmentsClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -205,7 +204,7 @@ export class EnvironmentsClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-orchestration-airflow-service/src/v1beta1/image_versions_client.ts b/packages/google-cloud-orchestration-airflow-service/src/v1beta1/image_versions_client.ts
index bd515298179..470d956ef15 100644
--- a/packages/google-cloud-orchestration-airflow-service/src/v1beta1/image_versions_client.ts
+++ b/packages/google-cloud-orchestration-airflow-service/src/v1beta1/image_versions_client.ts
@@ -90,8 +90,7 @@ export class ImageVersionsClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -99,7 +98,7 @@ export class ImageVersionsClient {
    *     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 ImageVersionsClient({fallback: 'rest'}, gax);
+   *     const client = new ImageVersionsClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -165,7 +164,7 @@ export class ImageVersionsClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
diff --git a/packages/google-cloud-orgpolicy/src/v2/org_policy_client.ts b/packages/google-cloud-orgpolicy/src/v2/org_policy_client.ts
index f09920a22d5..816385b84d2 100644
--- a/packages/google-cloud-orgpolicy/src/v2/org_policy_client.ts
+++ b/packages/google-cloud-orgpolicy/src/v2/org_policy_client.ts
@@ -109,8 +109,7 @@ export class OrgPolicyClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -118,7 +117,7 @@ export class OrgPolicyClient {
    *     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 OrgPolicyClient({fallback: 'rest'}, gax);
+   *     const client = new OrgPolicyClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -184,7 +183,7 @@ export class OrgPolicyClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
diff --git a/packages/google-cloud-osconfig/src/v1/os_config_service_client.ts b/packages/google-cloud-osconfig/src/v1/os_config_service_client.ts
index 8d7244562b4..749679b89d3 100644
--- a/packages/google-cloud-osconfig/src/v1/os_config_service_client.ts
+++ b/packages/google-cloud-osconfig/src/v1/os_config_service_client.ts
@@ -93,8 +93,7 @@ export class OsConfigServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -102,7 +101,7 @@ export class OsConfigServiceClient {
    *     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 OsConfigServiceClient({fallback: 'rest'}, gax);
+   *     const client = new OsConfigServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -168,7 +167,7 @@ export class OsConfigServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
diff --git a/packages/google-cloud-osconfig/src/v1/os_config_zonal_service_client.ts b/packages/google-cloud-osconfig/src/v1/os_config_zonal_service_client.ts
index 9cc9479d153..56fba8181fb 100644
--- a/packages/google-cloud-osconfig/src/v1/os_config_zonal_service_client.ts
+++ b/packages/google-cloud-osconfig/src/v1/os_config_zonal_service_client.ts
@@ -96,8 +96,7 @@ export class OsConfigZonalServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -105,7 +104,7 @@ export class OsConfigZonalServiceClient {
    *     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 OsConfigZonalServiceClient({fallback: 'rest'}, gax);
+   *     const client = new OsConfigZonalServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -171,7 +170,7 @@ export class OsConfigZonalServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -243,7 +242,7 @@ export class OsConfigZonalServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-osconfig/src/v1alpha/os_config_zonal_service_client.ts b/packages/google-cloud-osconfig/src/v1alpha/os_config_zonal_service_client.ts
index 0064d16b354..2e332a336de 100644
--- a/packages/google-cloud-osconfig/src/v1alpha/os_config_zonal_service_client.ts
+++ b/packages/google-cloud-osconfig/src/v1alpha/os_config_zonal_service_client.ts
@@ -96,8 +96,7 @@ export class OsConfigZonalServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -105,7 +104,7 @@ export class OsConfigZonalServiceClient {
    *     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 OsConfigZonalServiceClient({fallback: 'rest'}, gax);
+   *     const client = new OsConfigZonalServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -171,7 +170,7 @@ export class OsConfigZonalServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -246,7 +245,7 @@ export class OsConfigZonalServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-osconfig/src/v1beta/os_config_service_client.ts b/packages/google-cloud-osconfig/src/v1beta/os_config_service_client.ts
index 1f8e9841b6e..faffb20265b 100644
--- a/packages/google-cloud-osconfig/src/v1beta/os_config_service_client.ts
+++ b/packages/google-cloud-osconfig/src/v1beta/os_config_service_client.ts
@@ -93,8 +93,7 @@ export class OsConfigServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -102,7 +101,7 @@ export class OsConfigServiceClient {
    *     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 OsConfigServiceClient({fallback: 'rest'}, gax);
+   *     const client = new OsConfigServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -168,7 +167,7 @@ export class OsConfigServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
diff --git a/packages/google-cloud-osconfig/test/gapic_os_config_zonal_service_v1alpha.ts b/packages/google-cloud-osconfig/test/gapic_os_config_zonal_service_v1alpha.ts
index 81edb933426..35cb3304303 100644
--- a/packages/google-cloud-osconfig/test/gapic_os_config_zonal_service_v1alpha.ts
+++ b/packages/google-cloud-osconfig/test/gapic_os_config_zonal_service_v1alpha.ts
@@ -2360,8 +2360,9 @@ describe('v1alpha.OsConfigZonalServiceClient', () => {
       ];
       client.innerApiCalls.listInstanceOsPoliciesCompliances =
         stubSimpleCall(expectedResponse);
-      const [response] =
-        await client.listInstanceOSPoliciesCompliances(request);
+      const [response] = await client.listInstanceOSPoliciesCompliances(
+        request
+      );
       assert(stub.calledOnce);
       assert.deepStrictEqual(response, expectedResponse);
       const actualRequest = (
diff --git a/packages/google-cloud-oslogin/src/v1/os_login_service_client.ts b/packages/google-cloud-oslogin/src/v1/os_login_service_client.ts
index e88d1762fce..f6ee17bdbf2 100644
--- a/packages/google-cloud-oslogin/src/v1/os_login_service_client.ts
+++ b/packages/google-cloud-oslogin/src/v1/os_login_service_client.ts
@@ -91,8 +91,7 @@ export class OsLoginServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -100,7 +99,7 @@ export class OsLoginServiceClient {
    *     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 OsLoginServiceClient({fallback: 'rest'}, gax);
+   *     const client = new OsLoginServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -166,7 +165,7 @@ export class OsLoginServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
diff --git a/packages/google-cloud-oslogin/src/v1beta/os_login_service_client.ts b/packages/google-cloud-oslogin/src/v1beta/os_login_service_client.ts
index 684bc8e540f..fb4ea735d23 100644
--- a/packages/google-cloud-oslogin/src/v1beta/os_login_service_client.ts
+++ b/packages/google-cloud-oslogin/src/v1beta/os_login_service_client.ts
@@ -91,8 +91,7 @@ export class OsLoginServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -100,7 +99,7 @@ export class OsLoginServiceClient {
    *     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 OsLoginServiceClient({fallback: 'rest'}, gax);
+   *     const client = new OsLoginServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -166,7 +165,7 @@ export class OsLoginServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
diff --git a/packages/google-cloud-phishingprotection/src/v1beta1/phishing_protection_service_v1_beta1_client.ts b/packages/google-cloud-phishingprotection/src/v1beta1/phishing_protection_service_v1_beta1_client.ts
index 3488aac0d16..f4466b6c014 100644
--- a/packages/google-cloud-phishingprotection/src/v1beta1/phishing_protection_service_v1_beta1_client.ts
+++ b/packages/google-cloud-phishingprotection/src/v1beta1/phishing_protection_service_v1_beta1_client.ts
@@ -88,8 +88,7 @@ export class PhishingProtectionServiceV1Beta1Client {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -97,7 +96,7 @@ export class PhishingProtectionServiceV1Beta1Client {
    *     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 PhishingProtectionServiceV1Beta1Client({fallback: 'rest'}, gax);
+   *     const client = new PhishingProtectionServiceV1Beta1Client({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -164,7 +163,7 @@ export class PhishingProtectionServiceV1Beta1Client {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
diff --git a/packages/google-cloud-policytroubleshooter-iam/src/v3/policy_troubleshooter_client.ts b/packages/google-cloud-policytroubleshooter-iam/src/v3/policy_troubleshooter_client.ts
index bb6f5e62357..8c9534731f3 100644
--- a/packages/google-cloud-policytroubleshooter-iam/src/v3/policy_troubleshooter_client.ts
+++ b/packages/google-cloud-policytroubleshooter-iam/src/v3/policy_troubleshooter_client.ts
@@ -89,8 +89,7 @@ export class PolicyTroubleshooterClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -98,7 +97,7 @@ export class PolicyTroubleshooterClient {
    *     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 PolicyTroubleshooterClient({fallback: 'rest'}, gax);
+   *     const client = new PolicyTroubleshooterClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -164,7 +163,7 @@ export class PolicyTroubleshooterClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
diff --git a/packages/google-cloud-policytroubleshooter-iam/src/v3beta/policy_troubleshooter_client.ts b/packages/google-cloud-policytroubleshooter-iam/src/v3beta/policy_troubleshooter_client.ts
index 7e6085598a2..06718c7b3cb 100644
--- a/packages/google-cloud-policytroubleshooter-iam/src/v3beta/policy_troubleshooter_client.ts
+++ b/packages/google-cloud-policytroubleshooter-iam/src/v3beta/policy_troubleshooter_client.ts
@@ -89,8 +89,7 @@ export class PolicyTroubleshooterClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -98,7 +97,7 @@ export class PolicyTroubleshooterClient {
    *     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 PolicyTroubleshooterClient({fallback: 'rest'}, gax);
+   *     const client = new PolicyTroubleshooterClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -164,7 +163,7 @@ export class PolicyTroubleshooterClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
diff --git a/packages/google-cloud-policytroubleshooter/src/v1/iam_checker_client.ts b/packages/google-cloud-policytroubleshooter/src/v1/iam_checker_client.ts
index 927145ad462..09015006ef8 100644
--- a/packages/google-cloud-policytroubleshooter/src/v1/iam_checker_client.ts
+++ b/packages/google-cloud-policytroubleshooter/src/v1/iam_checker_client.ts
@@ -89,8 +89,7 @@ export class IamCheckerClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -98,7 +97,7 @@ export class IamCheckerClient {
    *     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 IamCheckerClient({fallback: 'rest'}, gax);
+   *     const client = new IamCheckerClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -164,7 +163,7 @@ export class IamCheckerClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
diff --git a/packages/google-cloud-privatecatalog/src/v1beta1/private_catalog_client.ts b/packages/google-cloud-privatecatalog/src/v1beta1/private_catalog_client.ts
index 13515cc5a38..8643eaf9d69 100644
--- a/packages/google-cloud-privatecatalog/src/v1beta1/private_catalog_client.ts
+++ b/packages/google-cloud-privatecatalog/src/v1beta1/private_catalog_client.ts
@@ -110,8 +110,7 @@ export class PrivateCatalogClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -119,7 +118,7 @@ export class PrivateCatalogClient {
    *     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 PrivateCatalogClient({fallback: 'rest'}, gax);
+   *     const client = new PrivateCatalogClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -185,7 +184,7 @@ export class PrivateCatalogClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
diff --git a/packages/google-cloud-rapidmigrationassessment/samples/quickstart.js b/packages/google-cloud-rapidmigrationassessment/samples/quickstart.js
index da9365b0314..6abe5d90d11 100644
--- a/packages/google-cloud-rapidmigrationassessment/samples/quickstart.js
+++ b/packages/google-cloud-rapidmigrationassessment/samples/quickstart.js
@@ -50,8 +50,9 @@ function main() {
       };
 
       // Run request
-      const iterable =
-        await rapidMigrationAssessmentClient.listCollectorsAsync(request);
+      const iterable = await rapidMigrationAssessmentClient.listCollectorsAsync(
+        request
+      );
       console.log(`Listing collectors for location ${location}:`);
       let count = 0;
       for await (const response of iterable) {
diff --git a/packages/google-cloud-rapidmigrationassessment/src/v1/rapid_migration_assessment_client.ts b/packages/google-cloud-rapidmigrationassessment/src/v1/rapid_migration_assessment_client.ts
index a0cc7d743b0..2a62e3a25df 100644
--- a/packages/google-cloud-rapidmigrationassessment/src/v1/rapid_migration_assessment_client.ts
+++ b/packages/google-cloud-rapidmigrationassessment/src/v1/rapid_migration_assessment_client.ts
@@ -96,8 +96,7 @@ export class RapidMigrationAssessmentClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -105,7 +104,7 @@ export class RapidMigrationAssessmentClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new RapidMigrationAssessmentClient({fallback: 'rest'}, gax);
+   *     const client = new RapidMigrationAssessmentClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -176,7 +175,7 @@ export class RapidMigrationAssessmentClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -219,7 +218,7 @@ export class RapidMigrationAssessmentClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-recaptchaenterprise/src/v1/recaptcha_enterprise_service_client.ts b/packages/google-cloud-recaptchaenterprise/src/v1/recaptcha_enterprise_service_client.ts
index eb537a509f2..85465a3336c 100644
--- a/packages/google-cloud-recaptchaenterprise/src/v1/recaptcha_enterprise_service_client.ts
+++ b/packages/google-cloud-recaptchaenterprise/src/v1/recaptcha_enterprise_service_client.ts
@@ -90,8 +90,7 @@ export class RecaptchaEnterpriseServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -99,7 +98,7 @@ export class RecaptchaEnterpriseServiceClient {
    *     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 RecaptchaEnterpriseServiceClient({fallback: 'rest'}, gax);
+   *     const client = new RecaptchaEnterpriseServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -166,7 +165,7 @@ export class RecaptchaEnterpriseServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
diff --git a/packages/google-cloud-recaptchaenterprise/src/v1beta1/recaptcha_enterprise_service_v1_beta1_client.ts b/packages/google-cloud-recaptchaenterprise/src/v1beta1/recaptcha_enterprise_service_v1_beta1_client.ts
index 4500aed63fe..ea3041c9f4f 100644
--- a/packages/google-cloud-recaptchaenterprise/src/v1beta1/recaptcha_enterprise_service_v1_beta1_client.ts
+++ b/packages/google-cloud-recaptchaenterprise/src/v1beta1/recaptcha_enterprise_service_v1_beta1_client.ts
@@ -88,8 +88,7 @@ export class RecaptchaEnterpriseServiceV1Beta1Client {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -97,7 +96,7 @@ export class RecaptchaEnterpriseServiceV1Beta1Client {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new RecaptchaEnterpriseServiceV1Beta1Client({fallback: 'rest'}, gax);
+   *     const client = new RecaptchaEnterpriseServiceV1Beta1Client({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -164,7 +163,7 @@ export class RecaptchaEnterpriseServiceV1Beta1Client {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
diff --git a/packages/google-cloud-recaptchaenterprise/test/gapic_recaptcha_enterprise_service_v1.ts b/packages/google-cloud-recaptchaenterprise/test/gapic_recaptcha_enterprise_service_v1.ts
index 85675c380fc..fcd953cd2cc 100644
--- a/packages/google-cloud-recaptchaenterprise/test/gapic_recaptcha_enterprise_service_v1.ts
+++ b/packages/google-cloud-recaptchaenterprise/test/gapic_recaptcha_enterprise_service_v1.ts
@@ -2285,8 +2285,9 @@ describe('v1.RecaptchaEnterpriseServiceClient', () => {
       ];
       client.innerApiCalls.listRelatedAccountGroupMemberships =
         stubSimpleCall(expectedResponse);
-      const [response] =
-        await client.listRelatedAccountGroupMemberships(request);
+      const [response] = await client.listRelatedAccountGroupMemberships(
+        request
+      );
       assert.deepStrictEqual(response, expectedResponse);
       const actualRequest = (
         client.innerApiCalls.listRelatedAccountGroupMemberships as SinonStub
@@ -2672,8 +2673,9 @@ describe('v1.RecaptchaEnterpriseServiceClient', () => {
       ];
       client.innerApiCalls.searchRelatedAccountGroupMemberships =
         stubSimpleCall(expectedResponse);
-      const [response] =
-        await client.searchRelatedAccountGroupMemberships(request);
+      const [response] = await client.searchRelatedAccountGroupMemberships(
+        request
+      );
       assert.deepStrictEqual(response, expectedResponse);
       const actualRequest = (
         client.innerApiCalls.searchRelatedAccountGroupMemberships as SinonStub
diff --git a/packages/google-cloud-recommender/src/v1/recommender_client.ts b/packages/google-cloud-recommender/src/v1/recommender_client.ts
index 07032bf1a43..4af5921abfe 100644
--- a/packages/google-cloud-recommender/src/v1/recommender_client.ts
+++ b/packages/google-cloud-recommender/src/v1/recommender_client.ts
@@ -93,8 +93,7 @@ export class RecommenderClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -102,7 +101,7 @@ export class RecommenderClient {
    *     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 RecommenderClient({fallback: 'rest'}, gax);
+   *     const client = new RecommenderClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -168,7 +167,7 @@ export class RecommenderClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
diff --git a/packages/google-cloud-recommender/src/v1beta1/recommender_client.ts b/packages/google-cloud-recommender/src/v1beta1/recommender_client.ts
index ba957e0f695..ebfedbfdddd 100644
--- a/packages/google-cloud-recommender/src/v1beta1/recommender_client.ts
+++ b/packages/google-cloud-recommender/src/v1beta1/recommender_client.ts
@@ -93,8 +93,7 @@ export class RecommenderClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -102,7 +101,7 @@ export class RecommenderClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new RecommenderClient({fallback: 'rest'}, gax);
+   *     const client = new RecommenderClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -168,7 +167,7 @@ export class RecommenderClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
diff --git a/packages/google-cloud-redis/src/v1/cloud_redis_client.ts b/packages/google-cloud-redis/src/v1/cloud_redis_client.ts
index 48361366c32..efb244d208b 100644
--- a/packages/google-cloud-redis/src/v1/cloud_redis_client.ts
+++ b/packages/google-cloud-redis/src/v1/cloud_redis_client.ts
@@ -110,8 +110,7 @@ export class CloudRedisClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -119,7 +118,7 @@ export class CloudRedisClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new CloudRedisClient({fallback: 'rest'}, gax);
+   *     const client = new CloudRedisClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -189,7 +188,7 @@ export class CloudRedisClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -229,7 +228,7 @@ export class CloudRedisClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-redis/src/v1beta1/cloud_redis_client.ts b/packages/google-cloud-redis/src/v1beta1/cloud_redis_client.ts
index ba4546c13a5..0b4f9050e52 100644
--- a/packages/google-cloud-redis/src/v1beta1/cloud_redis_client.ts
+++ b/packages/google-cloud-redis/src/v1beta1/cloud_redis_client.ts
@@ -107,8 +107,7 @@ export class CloudRedisClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -116,7 +115,7 @@ export class CloudRedisClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new CloudRedisClient({fallback: 'rest'}, gax);
+   *     const client = new CloudRedisClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -182,7 +181,7 @@ export class CloudRedisClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -222,7 +221,7 @@ export class CloudRedisClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-resourcemanager/src/v3/folders_client.ts b/packages/google-cloud-resourcemanager/src/v3/folders_client.ts
index ed01ef15bdd..99d616268f7 100644
--- a/packages/google-cloud-resourcemanager/src/v3/folders_client.ts
+++ b/packages/google-cloud-resourcemanager/src/v3/folders_client.ts
@@ -95,8 +95,7 @@ export class FoldersClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -104,7 +103,7 @@ export class FoldersClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new FoldersClient({fallback: 'rest'}, gax);
+   *     const client = new FoldersClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -170,7 +169,7 @@ export class FoldersClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -226,7 +225,7 @@ export class FoldersClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-resourcemanager/src/v3/organizations_client.ts b/packages/google-cloud-resourcemanager/src/v3/organizations_client.ts
index 1d2c3d8286f..8f384bf18ee 100644
--- a/packages/google-cloud-resourcemanager/src/v3/organizations_client.ts
+++ b/packages/google-cloud-resourcemanager/src/v3/organizations_client.ts
@@ -90,8 +90,7 @@ export class OrganizationsClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -99,7 +98,7 @@ export class OrganizationsClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new OrganizationsClient({fallback: 'rest'}, gax);
+   *     const client = new OrganizationsClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -165,7 +164,7 @@ export class OrganizationsClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
diff --git a/packages/google-cloud-resourcemanager/src/v3/projects_client.ts b/packages/google-cloud-resourcemanager/src/v3/projects_client.ts
index 1aa37d49376..a6fe69dd066 100644
--- a/packages/google-cloud-resourcemanager/src/v3/projects_client.ts
+++ b/packages/google-cloud-resourcemanager/src/v3/projects_client.ts
@@ -93,8 +93,7 @@ export class ProjectsClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -102,7 +101,7 @@ export class ProjectsClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new ProjectsClient({fallback: 'rest'}, gax);
+   *     const client = new ProjectsClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -168,7 +167,7 @@ export class ProjectsClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -224,7 +223,7 @@ export class ProjectsClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-resourcemanager/src/v3/tag_bindings_client.ts b/packages/google-cloud-resourcemanager/src/v3/tag_bindings_client.ts
index 65105fd63ef..7ceaf0fc8e4 100644
--- a/packages/google-cloud-resourcemanager/src/v3/tag_bindings_client.ts
+++ b/packages/google-cloud-resourcemanager/src/v3/tag_bindings_client.ts
@@ -94,8 +94,7 @@ export class TagBindingsClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -103,7 +102,7 @@ export class TagBindingsClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new TagBindingsClient({fallback: 'rest'}, gax);
+   *     const client = new TagBindingsClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -169,7 +168,7 @@ export class TagBindingsClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -225,7 +224,7 @@ export class TagBindingsClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-resourcemanager/src/v3/tag_holds_client.ts b/packages/google-cloud-resourcemanager/src/v3/tag_holds_client.ts
index 4d3b87f556e..6464e53760e 100644
--- a/packages/google-cloud-resourcemanager/src/v3/tag_holds_client.ts
+++ b/packages/google-cloud-resourcemanager/src/v3/tag_holds_client.ts
@@ -97,8 +97,7 @@ export class TagHoldsClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -106,7 +105,7 @@ export class TagHoldsClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new TagHoldsClient({fallback: 'rest'}, gax);
+   *     const client = new TagHoldsClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -172,7 +171,7 @@ export class TagHoldsClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -223,7 +222,7 @@ export class TagHoldsClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-resourcemanager/src/v3/tag_keys_client.ts b/packages/google-cloud-resourcemanager/src/v3/tag_keys_client.ts
index 630ceef32b3..adf3dc46560 100644
--- a/packages/google-cloud-resourcemanager/src/v3/tag_keys_client.ts
+++ b/packages/google-cloud-resourcemanager/src/v3/tag_keys_client.ts
@@ -93,8 +93,7 @@ export class TagKeysClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -102,7 +101,7 @@ export class TagKeysClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new TagKeysClient({fallback: 'rest'}, gax);
+   *     const client = new TagKeysClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -168,7 +167,7 @@ export class TagKeysClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -219,7 +218,7 @@ export class TagKeysClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-resourcemanager/src/v3/tag_values_client.ts b/packages/google-cloud-resourcemanager/src/v3/tag_values_client.ts
index 8a7774a1701..79cbe33108f 100644
--- a/packages/google-cloud-resourcemanager/src/v3/tag_values_client.ts
+++ b/packages/google-cloud-resourcemanager/src/v3/tag_values_client.ts
@@ -93,8 +93,7 @@ export class TagValuesClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -102,7 +101,7 @@ export class TagValuesClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new TagValuesClient({fallback: 'rest'}, gax);
+   *     const client = new TagValuesClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -168,7 +167,7 @@ export class TagValuesClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -219,7 +218,7 @@ export class TagValuesClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-resourcesettings/src/v1/resource_settings_service_client.ts b/packages/google-cloud-resourcesettings/src/v1/resource_settings_service_client.ts
index 9e297c40423..eb0d9272249 100644
--- a/packages/google-cloud-resourcesettings/src/v1/resource_settings_service_client.ts
+++ b/packages/google-cloud-resourcesettings/src/v1/resource_settings_service_client.ts
@@ -101,8 +101,7 @@ export class ResourceSettingsServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -110,7 +109,7 @@ export class ResourceSettingsServiceClient {
    *     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 ResourceSettingsServiceClient({fallback: 'rest'}, gax);
+   *     const client = new ResourceSettingsServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class ResourceSettingsServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
diff --git a/packages/google-cloud-retail/src/v2/catalog_service_client.ts b/packages/google-cloud-retail/src/v2/catalog_service_client.ts
index af689c2cfef..4295d10a92a 100644
--- a/packages/google-cloud-retail/src/v2/catalog_service_client.ts
+++ b/packages/google-cloud-retail/src/v2/catalog_service_client.ts
@@ -95,8 +95,7 @@ export class CatalogServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -104,7 +103,7 @@ export class CatalogServiceClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new CatalogServiceClient({fallback: 'rest'}, gax);
+   *     const client = new CatalogServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -174,7 +173,7 @@ export class CatalogServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -235,7 +234,7 @@ export class CatalogServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2/completion_service_client.ts b/packages/google-cloud-retail/src/v2/completion_service_client.ts
index 7a84fd9af5a..7fd17b3dc98 100644
--- a/packages/google-cloud-retail/src/v2/completion_service_client.ts
+++ b/packages/google-cloud-retail/src/v2/completion_service_client.ts
@@ -97,8 +97,7 @@ export class CompletionServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -106,7 +105,7 @@ export class CompletionServiceClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new CompletionServiceClient({fallback: 'rest'}, gax);
+   *     const client = new CompletionServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -176,7 +175,7 @@ export class CompletionServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -220,7 +219,7 @@ export class CompletionServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2/control_service_client.ts b/packages/google-cloud-retail/src/v2/control_service_client.ts
index 75b65e900e9..d1c35afc9c2 100644
--- a/packages/google-cloud-retail/src/v2/control_service_client.ts
+++ b/packages/google-cloud-retail/src/v2/control_service_client.ts
@@ -95,8 +95,7 @@ export class ControlServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -104,7 +103,7 @@ export class ControlServiceClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new ControlServiceClient({fallback: 'rest'}, gax);
+   *     const client = new ControlServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -174,7 +173,7 @@ export class ControlServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -229,7 +228,7 @@ export class ControlServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2/model_service_client.ts b/packages/google-cloud-retail/src/v2/model_service_client.ts
index 176f53a1c2a..ebe3f79e326 100644
--- a/packages/google-cloud-retail/src/v2/model_service_client.ts
+++ b/packages/google-cloud-retail/src/v2/model_service_client.ts
@@ -107,8 +107,7 @@ export class ModelServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -116,7 +115,7 @@ export class ModelServiceClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new ModelServiceClient({fallback: 'rest'}, gax);
+   *     const client = new ModelServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -186,7 +185,7 @@ export class ModelServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -241,7 +240,7 @@ export class ModelServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2/prediction_service_client.ts b/packages/google-cloud-retail/src/v2/prediction_service_client.ts
index cfa9de0d5fb..758ab693a08 100644
--- a/packages/google-cloud-retail/src/v2/prediction_service_client.ts
+++ b/packages/google-cloud-retail/src/v2/prediction_service_client.ts
@@ -93,8 +93,7 @@ export class PredictionServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -102,7 +101,7 @@ export class PredictionServiceClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new PredictionServiceClient({fallback: 'rest'}, gax);
+   *     const client = new PredictionServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -172,7 +171,7 @@ export class PredictionServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -216,7 +215,7 @@ export class PredictionServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2/product_service_client.ts b/packages/google-cloud-retail/src/v2/product_service_client.ts
index be0933b3772..55db9b357e4 100644
--- a/packages/google-cloud-retail/src/v2/product_service_client.ts
+++ b/packages/google-cloud-retail/src/v2/product_service_client.ts
@@ -97,8 +97,7 @@ export class ProductServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -106,7 +105,7 @@ export class ProductServiceClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new ProductServiceClient({fallback: 'rest'}, gax);
+   *     const client = new ProductServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -176,7 +175,7 @@ export class ProductServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -234,7 +233,7 @@ export class ProductServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2/search_service_client.ts b/packages/google-cloud-retail/src/v2/search_service_client.ts
index c8e543df531..eb4e9b1ee24 100644
--- a/packages/google-cloud-retail/src/v2/search_service_client.ts
+++ b/packages/google-cloud-retail/src/v2/search_service_client.ts
@@ -98,8 +98,7 @@ export class SearchServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -107,7 +106,7 @@ export class SearchServiceClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new SearchServiceClient({fallback: 'rest'}, gax);
+   *     const client = new SearchServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class SearchServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -238,7 +237,7 @@ export class SearchServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2/serving_config_service_client.ts b/packages/google-cloud-retail/src/v2/serving_config_service_client.ts
index b93f51fe54b..07e2b9b4de5 100644
--- a/packages/google-cloud-retail/src/v2/serving_config_service_client.ts
+++ b/packages/google-cloud-retail/src/v2/serving_config_service_client.ts
@@ -95,8 +95,7 @@ export class ServingConfigServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -104,7 +103,7 @@ export class ServingConfigServiceClient {
    *     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 ServingConfigServiceClient({fallback: 'rest'}, gax);
+   *     const client = new ServingConfigServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -174,7 +173,7 @@ export class ServingConfigServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -229,7 +228,7 @@ export class ServingConfigServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2/user_event_service_client.ts b/packages/google-cloud-retail/src/v2/user_event_service_client.ts
index 39070ef62bd..fea39714637 100644
--- a/packages/google-cloud-retail/src/v2/user_event_service_client.ts
+++ b/packages/google-cloud-retail/src/v2/user_event_service_client.ts
@@ -94,8 +94,7 @@ export class UserEventServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -103,7 +102,7 @@ export class UserEventServiceClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new UserEventServiceClient({fallback: 'rest'}, gax);
+   *     const client = new UserEventServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -173,7 +172,7 @@ export class UserEventServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -217,7 +216,7 @@ export class UserEventServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2alpha/catalog_service_client.ts b/packages/google-cloud-retail/src/v2alpha/catalog_service_client.ts
index 36ca640159d..50bef1d244e 100644
--- a/packages/google-cloud-retail/src/v2alpha/catalog_service_client.ts
+++ b/packages/google-cloud-retail/src/v2alpha/catalog_service_client.ts
@@ -95,8 +95,7 @@ export class CatalogServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -104,7 +103,7 @@ export class CatalogServiceClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new CatalogServiceClient({fallback: 'rest'}, gax);
+   *     const client = new CatalogServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -174,7 +173,7 @@ export class CatalogServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -238,7 +237,7 @@ export class CatalogServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2alpha/completion_service_client.ts b/packages/google-cloud-retail/src/v2alpha/completion_service_client.ts
index 9c0658571f3..856594fa292 100644
--- a/packages/google-cloud-retail/src/v2alpha/completion_service_client.ts
+++ b/packages/google-cloud-retail/src/v2alpha/completion_service_client.ts
@@ -97,8 +97,7 @@ export class CompletionServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -106,7 +105,7 @@ export class CompletionServiceClient {
    *     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 CompletionServiceClient({fallback: 'rest'}, gax);
+   *     const client = new CompletionServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -176,7 +175,7 @@ export class CompletionServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -223,7 +222,7 @@ export class CompletionServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2alpha/control_service_client.ts b/packages/google-cloud-retail/src/v2alpha/control_service_client.ts
index a9e5f611f1c..4b3d0593fa1 100644
--- a/packages/google-cloud-retail/src/v2alpha/control_service_client.ts
+++ b/packages/google-cloud-retail/src/v2alpha/control_service_client.ts
@@ -95,8 +95,7 @@ export class ControlServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -104,7 +103,7 @@ export class ControlServiceClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new ControlServiceClient({fallback: 'rest'}, gax);
+   *     const client = new ControlServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -174,7 +173,7 @@ export class ControlServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -232,7 +231,7 @@ export class ControlServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2alpha/merchant_center_account_link_service_client.ts b/packages/google-cloud-retail/src/v2alpha/merchant_center_account_link_service_client.ts
index 936b834342d..1916719d1e8 100644
--- a/packages/google-cloud-retail/src/v2alpha/merchant_center_account_link_service_client.ts
+++ b/packages/google-cloud-retail/src/v2alpha/merchant_center_account_link_service_client.ts
@@ -94,8 +94,7 @@ export class MerchantCenterAccountLinkServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -103,7 +102,7 @@ export class MerchantCenterAccountLinkServiceClient {
    *     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 MerchantCenterAccountLinkServiceClient({fallback: 'rest'}, gax);
+   *     const client = new MerchantCenterAccountLinkServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -174,7 +173,7 @@ export class MerchantCenterAccountLinkServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -221,7 +220,7 @@ export class MerchantCenterAccountLinkServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2alpha/model_service_client.ts b/packages/google-cloud-retail/src/v2alpha/model_service_client.ts
index 27dea1669b2..8c70c9f85cf 100644
--- a/packages/google-cloud-retail/src/v2alpha/model_service_client.ts
+++ b/packages/google-cloud-retail/src/v2alpha/model_service_client.ts
@@ -107,8 +107,7 @@ export class ModelServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -116,7 +115,7 @@ export class ModelServiceClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new ModelServiceClient({fallback: 'rest'}, gax);
+   *     const client = new ModelServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -186,7 +185,7 @@ export class ModelServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -244,7 +243,7 @@ export class ModelServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2alpha/prediction_service_client.ts b/packages/google-cloud-retail/src/v2alpha/prediction_service_client.ts
index 3abab007376..162bfb5522e 100644
--- a/packages/google-cloud-retail/src/v2alpha/prediction_service_client.ts
+++ b/packages/google-cloud-retail/src/v2alpha/prediction_service_client.ts
@@ -93,8 +93,7 @@ export class PredictionServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -102,7 +101,7 @@ export class PredictionServiceClient {
    *     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 PredictionServiceClient({fallback: 'rest'}, gax);
+   *     const client = new PredictionServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -172,7 +171,7 @@ export class PredictionServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -219,7 +218,7 @@ export class PredictionServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2alpha/product_service_client.ts b/packages/google-cloud-retail/src/v2alpha/product_service_client.ts
index 18d5479e136..36663491d6f 100644
--- a/packages/google-cloud-retail/src/v2alpha/product_service_client.ts
+++ b/packages/google-cloud-retail/src/v2alpha/product_service_client.ts
@@ -97,8 +97,7 @@ export class ProductServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -106,7 +105,7 @@ export class ProductServiceClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new ProductServiceClient({fallback: 'rest'}, gax);
+   *     const client = new ProductServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -176,7 +175,7 @@ export class ProductServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -237,7 +236,7 @@ export class ProductServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2alpha/search_service_client.ts b/packages/google-cloud-retail/src/v2alpha/search_service_client.ts
index 7c3b893d7e5..f544c45c10b 100644
--- a/packages/google-cloud-retail/src/v2alpha/search_service_client.ts
+++ b/packages/google-cloud-retail/src/v2alpha/search_service_client.ts
@@ -98,8 +98,7 @@ export class SearchServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -107,7 +106,7 @@ export class SearchServiceClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new SearchServiceClient({fallback: 'rest'}, gax);
+   *     const client = new SearchServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class SearchServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -241,7 +240,7 @@ export class SearchServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2alpha/serving_config_service_client.ts b/packages/google-cloud-retail/src/v2alpha/serving_config_service_client.ts
index 9d55ecd95f5..3b68fcc528c 100644
--- a/packages/google-cloud-retail/src/v2alpha/serving_config_service_client.ts
+++ b/packages/google-cloud-retail/src/v2alpha/serving_config_service_client.ts
@@ -95,8 +95,7 @@ export class ServingConfigServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -104,7 +103,7 @@ export class ServingConfigServiceClient {
    *     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 ServingConfigServiceClient({fallback: 'rest'}, gax);
+   *     const client = new ServingConfigServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -174,7 +173,7 @@ export class ServingConfigServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -232,7 +231,7 @@ export class ServingConfigServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2alpha/user_event_service_client.ts b/packages/google-cloud-retail/src/v2alpha/user_event_service_client.ts
index 2d9d4db496b..bd9267dcec8 100644
--- a/packages/google-cloud-retail/src/v2alpha/user_event_service_client.ts
+++ b/packages/google-cloud-retail/src/v2alpha/user_event_service_client.ts
@@ -94,8 +94,7 @@ export class UserEventServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -103,7 +102,7 @@ export class UserEventServiceClient {
    *     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 UserEventServiceClient({fallback: 'rest'}, gax);
+   *     const client = new UserEventServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -173,7 +172,7 @@ export class UserEventServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -220,7 +219,7 @@ export class UserEventServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2beta/catalog_service_client.ts b/packages/google-cloud-retail/src/v2beta/catalog_service_client.ts
index ab932a8caf3..ec9f784eb41 100644
--- a/packages/google-cloud-retail/src/v2beta/catalog_service_client.ts
+++ b/packages/google-cloud-retail/src/v2beta/catalog_service_client.ts
@@ -95,8 +95,7 @@ export class CatalogServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -104,7 +103,7 @@ export class CatalogServiceClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new CatalogServiceClient({fallback: 'rest'}, gax);
+   *     const client = new CatalogServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -174,7 +173,7 @@ export class CatalogServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -235,7 +234,7 @@ export class CatalogServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2beta/completion_service_client.ts b/packages/google-cloud-retail/src/v2beta/completion_service_client.ts
index 6ea6fbc398a..1e5f9463b5b 100644
--- a/packages/google-cloud-retail/src/v2beta/completion_service_client.ts
+++ b/packages/google-cloud-retail/src/v2beta/completion_service_client.ts
@@ -97,8 +97,7 @@ export class CompletionServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -106,7 +105,7 @@ export class CompletionServiceClient {
    *     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 CompletionServiceClient({fallback: 'rest'}, gax);
+   *     const client = new CompletionServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -176,7 +175,7 @@ export class CompletionServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -220,7 +219,7 @@ export class CompletionServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2beta/control_service_client.ts b/packages/google-cloud-retail/src/v2beta/control_service_client.ts
index d436ae5516b..8d48005069a 100644
--- a/packages/google-cloud-retail/src/v2beta/control_service_client.ts
+++ b/packages/google-cloud-retail/src/v2beta/control_service_client.ts
@@ -95,8 +95,7 @@ export class ControlServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -104,7 +103,7 @@ export class ControlServiceClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new ControlServiceClient({fallback: 'rest'}, gax);
+   *     const client = new ControlServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -174,7 +173,7 @@ export class ControlServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -229,7 +228,7 @@ export class ControlServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2beta/model_service_client.ts b/packages/google-cloud-retail/src/v2beta/model_service_client.ts
index e005e3e0fcb..806eabb91b4 100644
--- a/packages/google-cloud-retail/src/v2beta/model_service_client.ts
+++ b/packages/google-cloud-retail/src/v2beta/model_service_client.ts
@@ -107,8 +107,7 @@ export class ModelServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -116,7 +115,7 @@ export class ModelServiceClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new ModelServiceClient({fallback: 'rest'}, gax);
+   *     const client = new ModelServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -186,7 +185,7 @@ export class ModelServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -241,7 +240,7 @@ export class ModelServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2beta/prediction_service_client.ts b/packages/google-cloud-retail/src/v2beta/prediction_service_client.ts
index 029e967a948..07a7ff9dd9b 100644
--- a/packages/google-cloud-retail/src/v2beta/prediction_service_client.ts
+++ b/packages/google-cloud-retail/src/v2beta/prediction_service_client.ts
@@ -93,8 +93,7 @@ export class PredictionServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -102,7 +101,7 @@ export class PredictionServiceClient {
    *     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 PredictionServiceClient({fallback: 'rest'}, gax);
+   *     const client = new PredictionServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -172,7 +171,7 @@ export class PredictionServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -216,7 +215,7 @@ export class PredictionServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2beta/product_service_client.ts b/packages/google-cloud-retail/src/v2beta/product_service_client.ts
index 6bce5b9d28f..7b11908e655 100644
--- a/packages/google-cloud-retail/src/v2beta/product_service_client.ts
+++ b/packages/google-cloud-retail/src/v2beta/product_service_client.ts
@@ -97,8 +97,7 @@ export class ProductServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -106,7 +105,7 @@ export class ProductServiceClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new ProductServiceClient({fallback: 'rest'}, gax);
+   *     const client = new ProductServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -176,7 +175,7 @@ export class ProductServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -234,7 +233,7 @@ export class ProductServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2beta/search_service_client.ts b/packages/google-cloud-retail/src/v2beta/search_service_client.ts
index 83dad1ab9a0..a4f3d61afb4 100644
--- a/packages/google-cloud-retail/src/v2beta/search_service_client.ts
+++ b/packages/google-cloud-retail/src/v2beta/search_service_client.ts
@@ -98,8 +98,7 @@ export class SearchServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -107,7 +106,7 @@ export class SearchServiceClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new SearchServiceClient({fallback: 'rest'}, gax);
+   *     const client = new SearchServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class SearchServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -238,7 +237,7 @@ export class SearchServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2beta/serving_config_service_client.ts b/packages/google-cloud-retail/src/v2beta/serving_config_service_client.ts
index 79b0d0be013..54d39627233 100644
--- a/packages/google-cloud-retail/src/v2beta/serving_config_service_client.ts
+++ b/packages/google-cloud-retail/src/v2beta/serving_config_service_client.ts
@@ -95,8 +95,7 @@ export class ServingConfigServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -104,7 +103,7 @@ export class ServingConfigServiceClient {
    *     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 ServingConfigServiceClient({fallback: 'rest'}, gax);
+   *     const client = new ServingConfigServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -174,7 +173,7 @@ export class ServingConfigServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -229,7 +228,7 @@ export class ServingConfigServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-retail/src/v2beta/user_event_service_client.ts b/packages/google-cloud-retail/src/v2beta/user_event_service_client.ts
index 601919fc73e..00351ba45c7 100644
--- a/packages/google-cloud-retail/src/v2beta/user_event_service_client.ts
+++ b/packages/google-cloud-retail/src/v2beta/user_event_service_client.ts
@@ -94,8 +94,7 @@ export class UserEventServiceClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     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
@@ -103,7 +102,7 @@ export class UserEventServiceClient {
    *     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 UserEventServiceClient({fallback: 'rest'}, gax);
+   *     const client = new UserEventServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -173,7 +172,7 @@ export class UserEventServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -217,7 +216,7 @@ export class UserEventServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-run/src/v2/executions_client.ts b/packages/google-cloud-run/src/v2/executions_client.ts
index a1bb5444769..d28a99d42e7 100644
--- a/packages/google-cloud-run/src/v2/executions_client.ts
+++ b/packages/google-cloud-run/src/v2/executions_client.ts
@@ -96,8 +96,7 @@ export class ExecutionsClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -105,7 +104,7 @@ export class ExecutionsClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new ExecutionsClient({fallback: 'rest'}, gax);
+   *     const client = new ExecutionsClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -175,7 +174,7 @@ export class ExecutionsClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -230,7 +229,7 @@ export class ExecutionsClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-run/src/v2/jobs_client.ts b/packages/google-cloud-run/src/v2/jobs_client.ts
index f79108184e5..9b665b00499 100644
--- a/packages/google-cloud-run/src/v2/jobs_client.ts
+++ b/packages/google-cloud-run/src/v2/jobs_client.ts
@@ -96,8 +96,7 @@ export class JobsClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -105,7 +104,7 @@ export class JobsClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new JobsClient({fallback: 'rest'}, gax);
+   *     const client = new JobsClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -175,7 +174,7 @@ export class JobsClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -230,7 +229,7 @@ export class JobsClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-run/src/v2/revisions_client.ts b/packages/google-cloud-run/src/v2/revisions_client.ts
index e740427b7e7..a90243f340d 100644
--- a/packages/google-cloud-run/src/v2/revisions_client.ts
+++ b/packages/google-cloud-run/src/v2/revisions_client.ts
@@ -96,8 +96,7 @@ export class RevisionsClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -105,7 +104,7 @@ export class RevisionsClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new RevisionsClient({fallback: 'rest'}, gax);
+   *     const client = new RevisionsClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -175,7 +174,7 @@ export class RevisionsClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -233,7 +232,7 @@ export class RevisionsClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-run/src/v2/services_client.ts b/packages/google-cloud-run/src/v2/services_client.ts
index 11862ebd810..ac8a888a312 100644
--- a/packages/google-cloud-run/src/v2/services_client.ts
+++ b/packages/google-cloud-run/src/v2/services_client.ts
@@ -96,8 +96,7 @@ export class ServicesClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -105,7 +104,7 @@ export class ServicesClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new ServicesClient({fallback: 'rest'}, gax);
+   *     const client = new ServicesClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -175,7 +174,7 @@ export class ServicesClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -230,7 +229,7 @@ export class ServicesClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/packages/google-cloud-run/src/v2/tasks_client.ts b/packages/google-cloud-run/src/v2/tasks_client.ts
index 8381ca6acef..db81f350017 100644
--- a/packages/google-cloud-run/src/v2/tasks_client.ts
+++ b/packages/google-cloud-run/src/v2/tasks_client.ts
@@ -93,8 +93,7 @@ export class TasksClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -102,7 +101,7 @@ export class TasksClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new TasksClient({fallback: 'rest'}, gax);
+   *     const client = new TasksClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -172,7 +171,7 @@ export class TasksClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
diff --git a/packages/google-cloud-scheduler/src/v1/cloud_scheduler_client.ts b/packages/google-cloud-scheduler/src/v1/cloud_scheduler_client.ts
index ddbab13fc2d..8be38fbca1a 100644
--- a/packages/google-cloud-scheduler/src/v1/cloud_scheduler_client.ts
+++ b/packages/google-cloud-scheduler/src/v1/cloud_scheduler_client.ts
@@ -94,8 +94,7 @@ export class CloudSchedulerClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -103,7 +102,7 @@ export class CloudSchedulerClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new CloudSchedulerClient({fallback: 'rest'}, gax);
+   *     const client = new CloudSchedulerClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -173,7 +172,7 @@ export class CloudSchedulerClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
diff --git a/packages/google-cloud-scheduler/src/v1beta1/cloud_scheduler_client.ts b/packages/google-cloud-scheduler/src/v1beta1/cloud_scheduler_client.ts
index 2bff0efb040..5e34d871e08 100644
--- a/packages/google-cloud-scheduler/src/v1beta1/cloud_scheduler_client.ts
+++ b/packages/google-cloud-scheduler/src/v1beta1/cloud_scheduler_client.ts
@@ -94,8 +94,7 @@ export class CloudSchedulerClient {
    *     API remote host.
    * @param {gax.ClientConfig} [options.clientConfig] - Client configuration override.
    *     Follows the structure of {@link gapicConfig}.
-   * @param {boolean | "rest"} [options.fallback] - Use HTTP fallback mode.
-   *     Pass "rest" to use HTTP/1.1 REST API instead of gRPC.
+   * @param {boolean} [options.fallback] - Use HTTP/1.1 REST mode.
    *     For more information, please check the
    *     {@link https://github.com/googleapis/gax-nodejs/blob/main/client-libraries.md#http11-rest-api-mode documentation}.
    * @param {gax} [gaxInstance]: loaded instance of `google-gax`. Useful if you
@@ -103,7 +102,7 @@ export class CloudSchedulerClient {
    *     HTTP implementation. Load only fallback version and pass it to the constructor:
    *     ```
    *     const gax = require('google-gax/build/src/fallback'); // avoids loading google-gax with gRPC
-   *     const client = new CloudSchedulerClient({fallback: 'rest'}, gax);
+   *     const client = new CloudSchedulerClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -173,7 +172,7 @@ export class CloudSchedulerClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {