diff --git a/packages/google-ai-generativelanguage/src/v1beta2/discuss_service_client.ts b/packages/google-ai-generativelanguage/src/v1beta2/discuss_service_client.ts
index d090592aadb..47e279d6760 100644
--- a/packages/google-ai-generativelanguage/src/v1beta2/discuss_service_client.ts
+++ b/packages/google-ai-generativelanguage/src/v1beta2/discuss_service_client.ts
@@ -91,8 +91,7 @@ export class DiscussServiceClient {
    *     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 DiscussServiceClient {
    *     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 DiscussServiceClient({fallback: 'rest'}, gax);
+   *     const client = new DiscussServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -166,7 +165,7 @@ export class DiscussServiceClient {
     }
     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-ai-generativelanguage/src/v1beta2/model_service_client.ts b/packages/google-ai-generativelanguage/src/v1beta2/model_service_client.ts
index 0aa245ff0a9..81c442b8160 100644
--- a/packages/google-ai-generativelanguage/src/v1beta2/model_service_client.ts
+++ b/packages/google-ai-generativelanguage/src/v1beta2/model_service_client.ts
@@ -90,8 +90,7 @@ 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
@@ -99,7 +98,7 @@ 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(
@@ -165,7 +164,7 @@ 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) {
diff --git a/packages/google-ai-generativelanguage/src/v1beta2/text_service_client.ts b/packages/google-ai-generativelanguage/src/v1beta2/text_service_client.ts
index 3822dd50311..c57f2b8d7a4 100644
--- a/packages/google-ai-generativelanguage/src/v1beta2/text_service_client.ts
+++ b/packages/google-ai-generativelanguage/src/v1beta2/text_service_client.ts
@@ -91,8 +91,7 @@ export class TextServiceClient {
    *     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 TextServiceClient {
    *     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 TextServiceClient({fallback: 'rest'}, gax);
+   *     const client = new TextServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -166,7 +165,7 @@ export class TextServiceClient {
     }
     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-analytics-admin/src/v1alpha/analytics_admin_service_client.ts b/packages/google-analytics-admin/src/v1alpha/analytics_admin_service_client.ts
index b1e6bcf4e1a..7f054f2303e 100644
--- a/packages/google-analytics-admin/src/v1alpha/analytics_admin_service_client.ts
+++ b/packages/google-analytics-admin/src/v1alpha/analytics_admin_service_client.ts
@@ -90,8 +90,7 @@ export class AnalyticsAdminServiceClient {
    *     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 AnalyticsAdminServiceClient {
    *     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 AnalyticsAdminServiceClient({fallback: 'rest'}, gax);
+   *     const client = new AnalyticsAdminServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -166,7 +165,7 @@ export class AnalyticsAdminServiceClient {
     }
     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-analytics-admin/src/v1beta/analytics_admin_service_client.ts b/packages/google-analytics-admin/src/v1beta/analytics_admin_service_client.ts
index 73f0bfe0e0d..72cbd5c4061 100644
--- a/packages/google-analytics-admin/src/v1beta/analytics_admin_service_client.ts
+++ b/packages/google-analytics-admin/src/v1beta/analytics_admin_service_client.ts
@@ -90,8 +90,7 @@ export class AnalyticsAdminServiceClient {
    *     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 AnalyticsAdminServiceClient {
    *     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 AnalyticsAdminServiceClient({fallback: 'rest'}, gax);
+   *     const client = new AnalyticsAdminServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -166,7 +165,7 @@ export class AnalyticsAdminServiceClient {
     }
     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-analytics-data/src/v1alpha/alpha_analytics_data_client.ts b/packages/google-analytics-data/src/v1alpha/alpha_analytics_data_client.ts
index d25a0d176d7..0d2505f05c7 100644
--- a/packages/google-analytics-data/src/v1alpha/alpha_analytics_data_client.ts
+++ b/packages/google-analytics-data/src/v1alpha/alpha_analytics_data_client.ts
@@ -93,8 +93,7 @@ export class AlphaAnalyticsDataClient {
    *     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 AlphaAnalyticsDataClient {
    *     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 AlphaAnalyticsDataClient({fallback: 'rest'}, gax);
+   *     const client = new AlphaAnalyticsDataClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -168,7 +167,7 @@ export class AlphaAnalyticsDataClient {
     }
     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) {
@@ -208,7 +207,7 @@ export class AlphaAnalyticsDataClient {
       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-analytics-data/src/v1beta/beta_analytics_data_client.ts b/packages/google-analytics-data/src/v1beta/beta_analytics_data_client.ts
index 2abacff9d93..3ca491dda7a 100644
--- a/packages/google-analytics-data/src/v1beta/beta_analytics_data_client.ts
+++ b/packages/google-analytics-data/src/v1beta/beta_analytics_data_client.ts
@@ -88,8 +88,7 @@ export class BetaAnalyticsDataClient {
    *     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 BetaAnalyticsDataClient {
    *     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 BetaAnalyticsDataClient({fallback: 'rest'}, gax);
+   *     const client = new BetaAnalyticsDataClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -163,7 +162,7 @@ export class BetaAnalyticsDataClient {
     }
     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-api-apikeys/src/v2/api_keys_client.ts b/packages/google-api-apikeys/src/v2/api_keys_client.ts
index 4933d736b78..8ad780530c6 100644
--- a/packages/google-api-apikeys/src/v2/api_keys_client.ts
+++ b/packages/google-api-apikeys/src/v2/api_keys_client.ts
@@ -93,8 +93,7 @@ export class ApiKeysClient {
    *     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 ApiKeysClient {
    *     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 ApiKeysClient({fallback: 'rest'}, gax);
+   *     const client = new ApiKeysClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -168,7 +167,7 @@ export class ApiKeysClient {
     }
     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) {
@@ -211,7 +210,7 @@ export class ApiKeysClient {
       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-api-servicecontrol/src/v1/quota_controller_client.ts b/packages/google-api-servicecontrol/src/v1/quota_controller_client.ts
index dedbe5d3600..017b3357fac 100644
--- a/packages/google-api-servicecontrol/src/v1/quota_controller_client.ts
+++ b/packages/google-api-servicecontrol/src/v1/quota_controller_client.ts
@@ -90,8 +90,7 @@ export class QuotaControllerClient {
    *     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 QuotaControllerClient {
    *     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 QuotaControllerClient({fallback: 'rest'}, gax);
+   *     const client = new QuotaControllerClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -165,7 +164,7 @@ export class QuotaControllerClient {
     }
     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-api-servicecontrol/src/v1/service_controller_client.ts b/packages/google-api-servicecontrol/src/v1/service_controller_client.ts
index 8cfb6d8eccb..6964b790621 100644
--- a/packages/google-api-servicecontrol/src/v1/service_controller_client.ts
+++ b/packages/google-api-servicecontrol/src/v1/service_controller_client.ts
@@ -90,8 +90,7 @@ export class ServiceControllerClient {
    *     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 ServiceControllerClient {
    *     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 ServiceControllerClient({fallback: 'rest'}, gax);
+   *     const client = new ServiceControllerClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -165,7 +164,7 @@ export class ServiceControllerClient {
     }
     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-api-servicecontrol/src/v2/service_controller_client.ts b/packages/google-api-servicecontrol/src/v2/service_controller_client.ts
index e86db2ec559..eb1162342ad 100644
--- a/packages/google-api-servicecontrol/src/v2/service_controller_client.ts
+++ b/packages/google-api-servicecontrol/src/v2/service_controller_client.ts
@@ -94,8 +94,7 @@ export class ServiceControllerClient {
    *     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 ServiceControllerClient {
    *     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 ServiceControllerClient({fallback: 'rest'}, gax);
+   *     const client = new ServiceControllerClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -169,7 +168,7 @@ export class ServiceControllerClient {
     }
     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-api-servicemanagement/src/v1/service_manager_client.ts b/packages/google-api-servicemanagement/src/v1/service_manager_client.ts
index ef6a8d0c27e..fcf40738166 100644
--- a/packages/google-api-servicemanagement/src/v1/service_manager_client.ts
+++ b/packages/google-api-servicemanagement/src/v1/service_manager_client.ts
@@ -96,8 +96,7 @@ export class ServiceManagerClient {
    *     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 ServiceManagerClient {
    *     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 ServiceManagerClient({fallback: 'rest'}, gax);
+   *     const client = new ServiceManagerClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -172,7 +171,7 @@ export class ServiceManagerClient {
     }
     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) {
@@ -210,7 +209,7 @@ export class ServiceManagerClient {
       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-api-serviceusage/src/v1/service_usage_client.ts b/packages/google-api-serviceusage/src/v1/service_usage_client.ts
index 4c952286bc8..165dc524ce0 100644
--- a/packages/google-api-serviceusage/src/v1/service_usage_client.ts
+++ b/packages/google-api-serviceusage/src/v1/service_usage_client.ts
@@ -96,8 +96,7 @@ export class ServiceUsageClient {
    *     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 ServiceUsageClient {
    *     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 ServiceUsageClient({fallback: 'rest'}, gax);
+   *     const client = new ServiceUsageClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -171,7 +170,7 @@ export class ServiceUsageClient {
     }
     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) {
@@ -199,7 +198,7 @@ export class ServiceUsageClient {
       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-api-serviceusage/src/v1beta1/service_usage_client.ts b/packages/google-api-serviceusage/src/v1beta1/service_usage_client.ts
index d1e0e48ff11..ea62bc06a68 100644
--- a/packages/google-api-serviceusage/src/v1beta1/service_usage_client.ts
+++ b/packages/google-api-serviceusage/src/v1beta1/service_usage_client.ts
@@ -92,8 +92,7 @@ export class ServiceUsageClient {
    *     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
@@ -101,7 +100,7 @@ export class ServiceUsageClient {
    *     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 ServiceUsageClient({fallback: 'rest'}, gax);
+   *     const client = new ServiceUsageClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -167,7 +166,7 @@ export class ServiceUsageClient {
     }
     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) {
@@ -210,7 +209,7 @@ export class ServiceUsageClient {
       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-appengine/src/v1/applications_client.ts b/packages/google-appengine/src/v1/applications_client.ts
index af17726ddcb..1786e28c32f 100644
--- a/packages/google-appengine/src/v1/applications_client.ts
+++ b/packages/google-appengine/src/v1/applications_client.ts
@@ -91,8 +91,7 @@ export class ApplicationsClient {
    *     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 ApplicationsClient {
    *     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 ApplicationsClient({fallback: 'rest'}, gax);
+   *     const client = new ApplicationsClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -166,7 +165,7 @@ export class ApplicationsClient {
     }
     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) {
@@ -192,7 +191,7 @@ export class ApplicationsClient {
       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-appengine/src/v1/authorized_certificates_client.ts b/packages/google-appengine/src/v1/authorized_certificates_client.ts
index c150779452d..994ea208b1d 100644
--- a/packages/google-appengine/src/v1/authorized_certificates_client.ts
+++ b/packages/google-appengine/src/v1/authorized_certificates_client.ts
@@ -91,8 +91,7 @@ export class AuthorizedCertificatesClient {
    *     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 AuthorizedCertificatesClient {
    *     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 AuthorizedCertificatesClient({fallback: 'rest'}, gax);
+   *     const client = new AuthorizedCertificatesClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -167,7 +166,7 @@ export class AuthorizedCertificatesClient {
     }
     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-appengine/src/v1/authorized_domains_client.ts b/packages/google-appengine/src/v1/authorized_domains_client.ts
index a7a5b809e1d..7382db05487 100644
--- a/packages/google-appengine/src/v1/authorized_domains_client.ts
+++ b/packages/google-appengine/src/v1/authorized_domains_client.ts
@@ -92,8 +92,7 @@ export class AuthorizedDomainsClient {
    *     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
@@ -101,7 +100,7 @@ export class AuthorizedDomainsClient {
    *     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 AuthorizedDomainsClient({fallback: 'rest'}, gax);
+   *     const client = new AuthorizedDomainsClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -167,7 +166,7 @@ export class AuthorizedDomainsClient {
     }
     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-appengine/src/v1/domain_mappings_client.ts b/packages/google-appengine/src/v1/domain_mappings_client.ts
index 1f70535c0ae..18ad4c3bd7b 100644
--- a/packages/google-appengine/src/v1/domain_mappings_client.ts
+++ b/packages/google-appengine/src/v1/domain_mappings_client.ts
@@ -93,8 +93,7 @@ export class DomainMappingsClient {
    *     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 DomainMappingsClient {
    *     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 DomainMappingsClient({fallback: 'rest'}, gax);
+   *     const client = new DomainMappingsClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -168,7 +167,7 @@ export class DomainMappingsClient {
     }
     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 DomainMappingsClient {
       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-appengine/src/v1/firewall_client.ts b/packages/google-appengine/src/v1/firewall_client.ts
index cf7c9cbb0e3..922c874d40f 100644
--- a/packages/google-appengine/src/v1/firewall_client.ts
+++ b/packages/google-appengine/src/v1/firewall_client.ts
@@ -99,8 +99,7 @@ export class FirewallClient {
    *     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 FirewallClient {
    *     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 FirewallClient({fallback: 'rest'}, gax);
+   *     const client = new FirewallClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -174,7 +173,7 @@ export class FirewallClient {
     }
     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-appengine/src/v1/instances_client.ts b/packages/google-appengine/src/v1/instances_client.ts
index 28c82dad520..b119e074ac5 100644
--- a/packages/google-appengine/src/v1/instances_client.ts
+++ b/packages/google-appengine/src/v1/instances_client.ts
@@ -93,8 +93,7 @@ export class InstancesClient {
    *     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 InstancesClient {
    *     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 InstancesClient({fallback: 'rest'}, gax);
+   *     const client = new InstancesClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -168,7 +167,7 @@ export class InstancesClient {
     }
     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 InstancesClient {
       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-appengine/src/v1/services_client.ts b/packages/google-appengine/src/v1/services_client.ts
index 4fd30d84c40..6b542acea71 100644
--- a/packages/google-appengine/src/v1/services_client.ts
+++ b/packages/google-appengine/src/v1/services_client.ts
@@ -93,8 +93,7 @@ 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
@@ -102,7 +101,7 @@ 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(
@@ -168,7 +167,7 @@ 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) {
@@ -205,7 +204,7 @@ 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-appengine/src/v1/versions_client.ts b/packages/google-appengine/src/v1/versions_client.ts
index 0f69b76b6c5..2633c2234ce 100644
--- a/packages/google-appengine/src/v1/versions_client.ts
+++ b/packages/google-appengine/src/v1/versions_client.ts
@@ -93,8 +93,7 @@ export class VersionsClient {
    *     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 VersionsClient {
    *     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 VersionsClient({fallback: 'rest'}, gax);
+   *     const client = new VersionsClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -168,7 +167,7 @@ export class VersionsClient {
     }
     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 VersionsClient {
       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-area120-tables/src/v1alpha1/tables_service_client.ts b/packages/google-area120-tables/src/v1alpha1/tables_service_client.ts
index d8cf9b6f55c..03eb9eb3e4c 100644
--- a/packages/google-area120-tables/src/v1alpha1/tables_service_client.ts
+++ b/packages/google-area120-tables/src/v1alpha1/tables_service_client.ts
@@ -101,8 +101,7 @@ export class TablesServiceClient {
    *     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 TablesServiceClient {
    *     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 TablesServiceClient({fallback: 'rest'}, gax);
+   *     const client = new TablesServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -176,7 +175,7 @@ export class TablesServiceClient {
     }
     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-accessapproval/src/v1/access_approval_client.ts b/packages/google-cloud-accessapproval/src/v1/access_approval_client.ts
index 71cc259131b..2444e8e6155 100644
--- a/packages/google-cloud-accessapproval/src/v1/access_approval_client.ts
+++ b/packages/google-cloud-accessapproval/src/v1/access_approval_client.ts
@@ -122,8 +122,7 @@ export class AccessApprovalClient {
    *     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
@@ -131,7 +130,7 @@ export class AccessApprovalClient {
    *     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 AccessApprovalClient({fallback: 'rest'}, gax);
+   *     const client = new AccessApprovalClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -197,7 +196,7 @@ export class AccessApprovalClient {
     }
     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-advisorynotifications/samples/quickstart.js b/packages/google-cloud-advisorynotifications/samples/quickstart.js
index 59d7169f784..e5727ea61c4 100644
--- a/packages/google-cloud-advisorynotifications/samples/quickstart.js
+++ b/packages/google-cloud-advisorynotifications/samples/quickstart.js
@@ -72,8 +72,9 @@ function main(parent) {
     };
 
     // Run request
-    const iterable =
-      await advisorynotificationsClient.listNotificationsAsync(request);
+    const iterable = await advisorynotificationsClient.listNotificationsAsync(
+      request
+    );
     for await (const response of iterable) {
       console.log(response);
     }
diff --git a/packages/google-cloud-advisorynotifications/src/v1/advisory_notifications_service_client.ts b/packages/google-cloud-advisorynotifications/src/v1/advisory_notifications_service_client.ts
index f6801fccae2..cd353dcaf89 100644
--- a/packages/google-cloud-advisorynotifications/src/v1/advisory_notifications_service_client.ts
+++ b/packages/google-cloud-advisorynotifications/src/v1/advisory_notifications_service_client.ts
@@ -90,8 +90,7 @@ export class AdvisoryNotificationsServiceClient {
    *     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 AdvisoryNotificationsServiceClient {
    *     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 AdvisoryNotificationsServiceClient({fallback: 'rest'}, gax);
+   *     const client = new AdvisoryNotificationsServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -166,7 +165,7 @@ export class AdvisoryNotificationsServiceClient {
     }
     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-aiplatform/src/v1/dataset_service_client.ts b/packages/google-cloud-aiplatform/src/v1/dataset_service_client.ts
index 451e227667e..6ae89a4bbcb 100644
--- a/packages/google-cloud-aiplatform/src/v1/dataset_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1/dataset_service_client.ts
@@ -99,8 +99,7 @@ export class DatasetServiceClient {
    *     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 DatasetServiceClient {
    *     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 DatasetServiceClient({fallback: 'rest'}, gax);
+   *     const client = new DatasetServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class DatasetServiceClient {
     }
     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) {
@@ -350,7 +349,7 @@ export class DatasetServiceClient {
       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-aiplatform/src/v1/endpoint_service_client.ts b/packages/google-cloud-aiplatform/src/v1/endpoint_service_client.ts
index 16629538e89..e557587f662 100644
--- a/packages/google-cloud-aiplatform/src/v1/endpoint_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1/endpoint_service_client.ts
@@ -99,8 +99,7 @@ export class EndpointServiceClient {
    *     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 EndpointServiceClient {
    *     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 EndpointServiceClient({fallback: 'rest'}, gax);
+   *     const client = new EndpointServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class EndpointServiceClient {
     }
     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) {
@@ -330,7 +329,7 @@ export class EndpointServiceClient {
       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-aiplatform/src/v1/featurestore_online_serving_service_client.ts b/packages/google-cloud-aiplatform/src/v1/featurestore_online_serving_service_client.ts
index 9e670f05c97..7b24e91a140 100644
--- a/packages/google-cloud-aiplatform/src/v1/featurestore_online_serving_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1/featurestore_online_serving_service_client.ts
@@ -94,8 +94,7 @@ export class FeaturestoreOnlineServingServiceClient {
    *     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 FeaturestoreOnlineServingServiceClient {
    *     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 FeaturestoreOnlineServingServiceClient({fallback: 'rest'}, gax);
+   *     const client = new FeaturestoreOnlineServingServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -173,7 +172,7 @@ export class FeaturestoreOnlineServingServiceClient {
     }
     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) {
@@ -309,7 +308,7 @@ export class FeaturestoreOnlineServingServiceClient {
     this.descriptors.stream = {
       streamingReadFeatureValues: new this._gaxModule.StreamDescriptor(
         this._gaxModule.StreamType.SERVER_STREAMING,
-        opts.fallback === 'rest'
+        !!opts.fallback
       ),
     };
 
diff --git a/packages/google-cloud-aiplatform/src/v1/featurestore_service_client.ts b/packages/google-cloud-aiplatform/src/v1/featurestore_service_client.ts
index 2ae99c331f4..cfae28d8594 100644
--- a/packages/google-cloud-aiplatform/src/v1/featurestore_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1/featurestore_service_client.ts
@@ -99,8 +99,7 @@ export class FeaturestoreServiceClient {
    *     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 FeaturestoreServiceClient {
    *     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 FeaturestoreServiceClient({fallback: 'rest'}, gax);
+   *     const client = new FeaturestoreServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class FeaturestoreServiceClient {
     }
     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) {
@@ -348,7 +347,7 @@ export class FeaturestoreServiceClient {
       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-aiplatform/src/v1/index_endpoint_service_client.ts b/packages/google-cloud-aiplatform/src/v1/index_endpoint_service_client.ts
index 7920378ac68..e865059953d 100644
--- a/packages/google-cloud-aiplatform/src/v1/index_endpoint_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1/index_endpoint_service_client.ts
@@ -99,8 +99,7 @@ export class IndexEndpointServiceClient {
    *     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 IndexEndpointServiceClient {
    *     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 IndexEndpointServiceClient({fallback: 'rest'}, gax);
+   *     const client = new IndexEndpointServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class IndexEndpointServiceClient {
     }
     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) {
@@ -330,7 +329,7 @@ export class IndexEndpointServiceClient {
       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-aiplatform/src/v1/index_service_client.ts b/packages/google-cloud-aiplatform/src/v1/index_service_client.ts
index fd03461d1d6..ee92297c942 100644
--- a/packages/google-cloud-aiplatform/src/v1/index_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1/index_service_client.ts
@@ -99,8 +99,7 @@ export class IndexServiceClient {
    *     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 IndexServiceClient {
    *     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 IndexServiceClient({fallback: 'rest'}, gax);
+   *     const client = new IndexServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class IndexServiceClient {
     }
     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) {
@@ -330,7 +329,7 @@ export class IndexServiceClient {
       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-aiplatform/src/v1/job_service_client.ts b/packages/google-cloud-aiplatform/src/v1/job_service_client.ts
index 4c3e80d5a5c..883b6443364 100644
--- a/packages/google-cloud-aiplatform/src/v1/job_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1/job_service_client.ts
@@ -99,8 +99,7 @@ export class JobServiceClient {
    *     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 JobServiceClient {
    *     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 JobServiceClient({fallback: 'rest'}, gax);
+   *     const client = new JobServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class JobServiceClient {
     }
     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) {
@@ -366,7 +365,7 @@ export class JobServiceClient {
       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-aiplatform/src/v1/match_service_client.ts b/packages/google-cloud-aiplatform/src/v1/match_service_client.ts
index 4890dc0772d..f4ffa3aab85 100644
--- a/packages/google-cloud-aiplatform/src/v1/match_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1/match_service_client.ts
@@ -95,8 +95,7 @@ export class MatchServiceClient {
    *     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 MatchServiceClient {
    *     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 MatchServiceClient({fallback: 'rest'}, gax);
+   *     const client = new MatchServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -173,7 +172,7 @@ export class MatchServiceClient {
     }
     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-aiplatform/src/v1/metadata_service_client.ts b/packages/google-cloud-aiplatform/src/v1/metadata_service_client.ts
index f1bae8dcc0c..04613e68093 100644
--- a/packages/google-cloud-aiplatform/src/v1/metadata_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1/metadata_service_client.ts
@@ -99,8 +99,7 @@ export class MetadataServiceClient {
    *     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 MetadataServiceClient {
    *     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 MetadataServiceClient({fallback: 'rest'}, gax);
+   *     const client = new MetadataServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class MetadataServiceClient {
     }
     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) {
@@ -353,7 +352,7 @@ export class MetadataServiceClient {
       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-aiplatform/src/v1/migration_service_client.ts b/packages/google-cloud-aiplatform/src/v1/migration_service_client.ts
index 9809814152e..c912bd318ad 100644
--- a/packages/google-cloud-aiplatform/src/v1/migration_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1/migration_service_client.ts
@@ -100,8 +100,7 @@ export class MigrationServiceClient {
    *     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
@@ -109,7 +108,7 @@ export class MigrationServiceClient {
    *     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 MigrationServiceClient({fallback: 'rest'}, gax);
+   *     const client = new MigrationServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -178,7 +177,7 @@ export class MigrationServiceClient {
     }
     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) {
@@ -331,7 +330,7 @@ export class MigrationServiceClient {
       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-aiplatform/src/v1/model_garden_service_client.ts b/packages/google-cloud-aiplatform/src/v1/model_garden_service_client.ts
index c8e2d1eba53..d600ceae84a 100644
--- a/packages/google-cloud-aiplatform/src/v1/model_garden_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1/model_garden_service_client.ts
@@ -94,8 +94,7 @@ export class ModelGardenServiceClient {
    *     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 ModelGardenServiceClient {
    *     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 ModelGardenServiceClient({fallback: 'rest'}, gax);
+   *     const client = new ModelGardenServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -172,7 +171,7 @@ export class ModelGardenServiceClient {
     }
     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-aiplatform/src/v1/model_service_client.ts b/packages/google-cloud-aiplatform/src/v1/model_service_client.ts
index 34118ff739c..4bfdf4349bf 100644
--- a/packages/google-cloud-aiplatform/src/v1/model_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1/model_service_client.ts
@@ -99,8 +99,7 @@ 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
@@ -108,7 +107,7 @@ 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(
@@ -177,7 +176,7 @@ 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) {
@@ -345,7 +344,7 @@ 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-aiplatform/src/v1/pipeline_service_client.ts b/packages/google-cloud-aiplatform/src/v1/pipeline_service_client.ts
index 18653f5f6ac..0ca13f2bb83 100644
--- a/packages/google-cloud-aiplatform/src/v1/pipeline_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1/pipeline_service_client.ts
@@ -101,8 +101,7 @@ export class PipelineServiceClient {
    *     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 PipelineServiceClient {
    *     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 PipelineServiceClient({fallback: 'rest'}, gax);
+   *     const client = new PipelineServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -179,7 +178,7 @@ export class PipelineServiceClient {
     }
     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) {
@@ -337,7 +336,7 @@ export class PipelineServiceClient {
       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-aiplatform/src/v1/prediction_service_client.ts b/packages/google-cloud-aiplatform/src/v1/prediction_service_client.ts
index 178222076c3..242ff434586 100644
--- a/packages/google-cloud-aiplatform/src/v1/prediction_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1/prediction_service_client.ts
@@ -94,8 +94,7 @@ 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
@@ -103,7 +102,7 @@ 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) {
@@ -308,7 +307,7 @@ export class PredictionServiceClient {
     this.descriptors.stream = {
       serverStreamingPredict: new this._gaxModule.StreamDescriptor(
         this._gaxModule.StreamType.SERVER_STREAMING,
-        opts.fallback === 'rest'
+        !!opts.fallback
       ),
     };
 
diff --git a/packages/google-cloud-aiplatform/src/v1/schedule_service_client.ts b/packages/google-cloud-aiplatform/src/v1/schedule_service_client.ts
index ce04c6802d2..7d8dc481127 100644
--- a/packages/google-cloud-aiplatform/src/v1/schedule_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1/schedule_service_client.ts
@@ -100,8 +100,7 @@ export class ScheduleServiceClient {
    *     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
@@ -109,7 +108,7 @@ export class ScheduleServiceClient {
    *     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 ScheduleServiceClient({fallback: 'rest'}, gax);
+   *     const client = new ScheduleServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -178,7 +177,7 @@ export class ScheduleServiceClient {
     }
     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) {
@@ -331,7 +330,7 @@ export class ScheduleServiceClient {
       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-aiplatform/src/v1/specialist_pool_service_client.ts b/packages/google-cloud-aiplatform/src/v1/specialist_pool_service_client.ts
index c5b874a44c7..e0fdd6ce39c 100644
--- a/packages/google-cloud-aiplatform/src/v1/specialist_pool_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1/specialist_pool_service_client.ts
@@ -104,8 +104,7 @@ export class SpecialistPoolServiceClient {
    *     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
@@ -113,7 +112,7 @@ export class SpecialistPoolServiceClient {
    *     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 SpecialistPoolServiceClient({fallback: 'rest'}, gax);
+   *     const client = new SpecialistPoolServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -183,7 +182,7 @@ export class SpecialistPoolServiceClient {
     }
     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) {
@@ -336,7 +335,7 @@ export class SpecialistPoolServiceClient {
       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-aiplatform/src/v1/tensorboard_service_client.ts b/packages/google-cloud-aiplatform/src/v1/tensorboard_service_client.ts
index e95e459ffbb..b97ad45db47 100644
--- a/packages/google-cloud-aiplatform/src/v1/tensorboard_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1/tensorboard_service_client.ts
@@ -99,8 +99,7 @@ export class TensorboardServiceClient {
    *     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 TensorboardServiceClient {
    *     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 TensorboardServiceClient({fallback: 'rest'}, gax);
+   *     const client = new TensorboardServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class TensorboardServiceClient {
     }
     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) {
@@ -350,7 +349,7 @@ export class TensorboardServiceClient {
     this.descriptors.stream = {
       readTensorboardBlobData: new this._gaxModule.StreamDescriptor(
         this._gaxModule.StreamType.SERVER_STREAMING,
-        opts.fallback === 'rest'
+        !!opts.fallback
       ),
     };
 
@@ -362,7 +361,7 @@ export class TensorboardServiceClient {
       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-aiplatform/src/v1/vizier_service_client.ts b/packages/google-cloud-aiplatform/src/v1/vizier_service_client.ts
index 31872cf8842..5fb12abd98e 100644
--- a/packages/google-cloud-aiplatform/src/v1/vizier_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1/vizier_service_client.ts
@@ -103,8 +103,7 @@ export class VizierServiceClient {
    *     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
@@ -112,7 +111,7 @@ export class VizierServiceClient {
    *     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 VizierServiceClient({fallback: 'rest'}, gax);
+   *     const client = new VizierServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -181,7 +180,7 @@ export class VizierServiceClient {
     }
     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) {
@@ -339,7 +338,7 @@ export class VizierServiceClient {
       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-aiplatform/src/v1beta1/dataset_service_client.ts b/packages/google-cloud-aiplatform/src/v1beta1/dataset_service_client.ts
index b4c87ea63fe..4331a6dc3a8 100644
--- a/packages/google-cloud-aiplatform/src/v1beta1/dataset_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1beta1/dataset_service_client.ts
@@ -99,8 +99,7 @@ export class DatasetServiceClient {
    *     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 DatasetServiceClient {
    *     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 DatasetServiceClient({fallback: 'rest'}, gax);
+   *     const client = new DatasetServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class DatasetServiceClient {
     }
     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) {
@@ -356,7 +355,7 @@ export class DatasetServiceClient {
       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-aiplatform/src/v1beta1/deployment_resource_pool_service_client.ts b/packages/google-cloud-aiplatform/src/v1beta1/deployment_resource_pool_service_client.ts
index f714d01a704..27a286a3744 100644
--- a/packages/google-cloud-aiplatform/src/v1beta1/deployment_resource_pool_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1beta1/deployment_resource_pool_service_client.ts
@@ -99,8 +99,7 @@ export class DeploymentResourcePoolServiceClient {
    *     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 DeploymentResourcePoolServiceClient {
    *     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 DeploymentResourcePoolServiceClient({fallback: 'rest'}, gax);
+   *     const client = new DeploymentResourcePoolServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -178,7 +177,7 @@ export class DeploymentResourcePoolServiceClient {
     }
     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) {
@@ -345,7 +344,7 @@ export class DeploymentResourcePoolServiceClient {
       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-aiplatform/src/v1beta1/endpoint_service_client.ts b/packages/google-cloud-aiplatform/src/v1beta1/endpoint_service_client.ts
index f2bdd7bf4e7..b0e60762a10 100644
--- a/packages/google-cloud-aiplatform/src/v1beta1/endpoint_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1beta1/endpoint_service_client.ts
@@ -99,8 +99,7 @@ export class EndpointServiceClient {
    *     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 EndpointServiceClient {
    *     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 EndpointServiceClient({fallback: 'rest'}, gax);
+   *     const client = new EndpointServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class EndpointServiceClient {
     }
     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) {
@@ -336,7 +335,7 @@ export class EndpointServiceClient {
       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-aiplatform/src/v1beta1/featurestore_online_serving_service_client.ts b/packages/google-cloud-aiplatform/src/v1beta1/featurestore_online_serving_service_client.ts
index ee8b0d800e0..e5a5aaf3787 100644
--- a/packages/google-cloud-aiplatform/src/v1beta1/featurestore_online_serving_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1beta1/featurestore_online_serving_service_client.ts
@@ -94,8 +94,7 @@ export class FeaturestoreOnlineServingServiceClient {
    *     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 FeaturestoreOnlineServingServiceClient {
    *     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 FeaturestoreOnlineServingServiceClient({fallback: 'rest'}, gax);
+   *     const client = new FeaturestoreOnlineServingServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -173,7 +172,7 @@ export class FeaturestoreOnlineServingServiceClient {
     }
     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) {
@@ -315,7 +314,7 @@ export class FeaturestoreOnlineServingServiceClient {
     this.descriptors.stream = {
       streamingReadFeatureValues: new this._gaxModule.StreamDescriptor(
         this._gaxModule.StreamType.SERVER_STREAMING,
-        opts.fallback === 'rest'
+        !!opts.fallback
       ),
     };
 
diff --git a/packages/google-cloud-aiplatform/src/v1beta1/featurestore_service_client.ts b/packages/google-cloud-aiplatform/src/v1beta1/featurestore_service_client.ts
index 86a3347b857..b61638cf698 100644
--- a/packages/google-cloud-aiplatform/src/v1beta1/featurestore_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1beta1/featurestore_service_client.ts
@@ -99,8 +99,7 @@ export class FeaturestoreServiceClient {
    *     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 FeaturestoreServiceClient {
    *     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 FeaturestoreServiceClient({fallback: 'rest'}, gax);
+   *     const client = new FeaturestoreServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class FeaturestoreServiceClient {
     }
     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) {
@@ -354,7 +353,7 @@ export class FeaturestoreServiceClient {
       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-aiplatform/src/v1beta1/index_endpoint_service_client.ts b/packages/google-cloud-aiplatform/src/v1beta1/index_endpoint_service_client.ts
index 956fe32e739..b22ad00f427 100644
--- a/packages/google-cloud-aiplatform/src/v1beta1/index_endpoint_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1beta1/index_endpoint_service_client.ts
@@ -99,8 +99,7 @@ export class IndexEndpointServiceClient {
    *     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 IndexEndpointServiceClient {
    *     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 IndexEndpointServiceClient({fallback: 'rest'}, gax);
+   *     const client = new IndexEndpointServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class IndexEndpointServiceClient {
     }
     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) {
@@ -336,7 +335,7 @@ export class IndexEndpointServiceClient {
       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-aiplatform/src/v1beta1/index_service_client.ts b/packages/google-cloud-aiplatform/src/v1beta1/index_service_client.ts
index eb24e14f6ab..32f97b495c1 100644
--- a/packages/google-cloud-aiplatform/src/v1beta1/index_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1beta1/index_service_client.ts
@@ -99,8 +99,7 @@ export class IndexServiceClient {
    *     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 IndexServiceClient {
    *     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 IndexServiceClient({fallback: 'rest'}, gax);
+   *     const client = new IndexServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class IndexServiceClient {
     }
     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) {
@@ -336,7 +335,7 @@ export class IndexServiceClient {
       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-aiplatform/src/v1beta1/job_service_client.ts b/packages/google-cloud-aiplatform/src/v1beta1/job_service_client.ts
index 435bd181e14..fb4a32d2b65 100644
--- a/packages/google-cloud-aiplatform/src/v1beta1/job_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1beta1/job_service_client.ts
@@ -99,8 +99,7 @@ export class JobServiceClient {
    *     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 JobServiceClient {
    *     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 JobServiceClient({fallback: 'rest'}, gax);
+   *     const client = new JobServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class JobServiceClient {
     }
     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) {
@@ -372,7 +371,7 @@ export class JobServiceClient {
       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-aiplatform/src/v1beta1/match_service_client.ts b/packages/google-cloud-aiplatform/src/v1beta1/match_service_client.ts
index 4993ed12e26..47279f5019c 100644
--- a/packages/google-cloud-aiplatform/src/v1beta1/match_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1beta1/match_service_client.ts
@@ -95,8 +95,7 @@ export class MatchServiceClient {
    *     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 MatchServiceClient {
    *     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 MatchServiceClient({fallback: 'rest'}, gax);
+   *     const client = new MatchServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -173,7 +172,7 @@ export class MatchServiceClient {
     }
     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-aiplatform/src/v1beta1/metadata_service_client.ts b/packages/google-cloud-aiplatform/src/v1beta1/metadata_service_client.ts
index 8e37d7c715e..0ef77f28d0b 100644
--- a/packages/google-cloud-aiplatform/src/v1beta1/metadata_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1beta1/metadata_service_client.ts
@@ -99,8 +99,7 @@ export class MetadataServiceClient {
    *     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 MetadataServiceClient {
    *     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 MetadataServiceClient({fallback: 'rest'}, gax);
+   *     const client = new MetadataServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class MetadataServiceClient {
     }
     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) {
@@ -359,7 +358,7 @@ export class MetadataServiceClient {
       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-aiplatform/src/v1beta1/migration_service_client.ts b/packages/google-cloud-aiplatform/src/v1beta1/migration_service_client.ts
index ae210b495ad..6920b50675f 100644
--- a/packages/google-cloud-aiplatform/src/v1beta1/migration_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1beta1/migration_service_client.ts
@@ -100,8 +100,7 @@ export class MigrationServiceClient {
    *     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
@@ -109,7 +108,7 @@ export class MigrationServiceClient {
    *     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 MigrationServiceClient({fallback: 'rest'}, gax);
+   *     const client = new MigrationServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -178,7 +177,7 @@ export class MigrationServiceClient {
     }
     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) {
@@ -337,7 +336,7 @@ export class MigrationServiceClient {
       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-aiplatform/src/v1beta1/model_garden_service_client.ts b/packages/google-cloud-aiplatform/src/v1beta1/model_garden_service_client.ts
index 7b91adb1192..00c6f870dbe 100644
--- a/packages/google-cloud-aiplatform/src/v1beta1/model_garden_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1beta1/model_garden_service_client.ts
@@ -94,8 +94,7 @@ export class ModelGardenServiceClient {
    *     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 ModelGardenServiceClient {
    *     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 ModelGardenServiceClient({fallback: 'rest'}, gax);
+   *     const client = new ModelGardenServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -172,7 +171,7 @@ export class ModelGardenServiceClient {
     }
     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-aiplatform/src/v1beta1/model_service_client.ts b/packages/google-cloud-aiplatform/src/v1beta1/model_service_client.ts
index d1ee76865b1..508a2ca347d 100644
--- a/packages/google-cloud-aiplatform/src/v1beta1/model_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1beta1/model_service_client.ts
@@ -99,8 +99,7 @@ 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
@@ -108,7 +107,7 @@ 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(
@@ -177,7 +176,7 @@ 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) {
@@ -351,7 +350,7 @@ 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-aiplatform/src/v1beta1/persistent_resource_service_client.ts b/packages/google-cloud-aiplatform/src/v1beta1/persistent_resource_service_client.ts
index 206ba811b0d..aaf5f450387 100644
--- a/packages/google-cloud-aiplatform/src/v1beta1/persistent_resource_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1beta1/persistent_resource_service_client.ts
@@ -99,8 +99,7 @@ export class PersistentResourceServiceClient {
    *     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 PersistentResourceServiceClient {
    *     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 PersistentResourceServiceClient({fallback: 'rest'}, gax);
+   *     const client = new PersistentResourceServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -178,7 +177,7 @@ export class PersistentResourceServiceClient {
     }
     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) {
@@ -337,7 +336,7 @@ export class PersistentResourceServiceClient {
       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-aiplatform/src/v1beta1/pipeline_service_client.ts b/packages/google-cloud-aiplatform/src/v1beta1/pipeline_service_client.ts
index b8403309964..339de351f4e 100644
--- a/packages/google-cloud-aiplatform/src/v1beta1/pipeline_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1beta1/pipeline_service_client.ts
@@ -101,8 +101,7 @@ export class PipelineServiceClient {
    *     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 PipelineServiceClient {
    *     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 PipelineServiceClient({fallback: 'rest'}, gax);
+   *     const client = new PipelineServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -179,7 +178,7 @@ export class PipelineServiceClient {
     }
     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) {
@@ -343,7 +342,7 @@ export class PipelineServiceClient {
       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-aiplatform/src/v1beta1/prediction_service_client.ts b/packages/google-cloud-aiplatform/src/v1beta1/prediction_service_client.ts
index 42e0570df0c..9e3d5872fa8 100644
--- a/packages/google-cloud-aiplatform/src/v1beta1/prediction_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1beta1/prediction_service_client.ts
@@ -94,8 +94,7 @@ 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
@@ -103,7 +102,7 @@ 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) {
@@ -314,7 +313,7 @@ export class PredictionServiceClient {
     this.descriptors.stream = {
       serverStreamingPredict: new this._gaxModule.StreamDescriptor(
         this._gaxModule.StreamType.SERVER_STREAMING,
-        opts.fallback === 'rest'
+        !!opts.fallback
       ),
     };
 
diff --git a/packages/google-cloud-aiplatform/src/v1beta1/schedule_service_client.ts b/packages/google-cloud-aiplatform/src/v1beta1/schedule_service_client.ts
index 720b955f66e..9a24adad109 100644
--- a/packages/google-cloud-aiplatform/src/v1beta1/schedule_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1beta1/schedule_service_client.ts
@@ -100,8 +100,7 @@ export class ScheduleServiceClient {
    *     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
@@ -109,7 +108,7 @@ export class ScheduleServiceClient {
    *     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 ScheduleServiceClient({fallback: 'rest'}, gax);
+   *     const client = new ScheduleServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -178,7 +177,7 @@ export class ScheduleServiceClient {
     }
     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) {
@@ -337,7 +336,7 @@ export class ScheduleServiceClient {
       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-aiplatform/src/v1beta1/specialist_pool_service_client.ts b/packages/google-cloud-aiplatform/src/v1beta1/specialist_pool_service_client.ts
index c70e2ca7f5d..a8a3841d333 100644
--- a/packages/google-cloud-aiplatform/src/v1beta1/specialist_pool_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1beta1/specialist_pool_service_client.ts
@@ -104,8 +104,7 @@ export class SpecialistPoolServiceClient {
    *     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
@@ -113,7 +112,7 @@ export class SpecialistPoolServiceClient {
    *     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 SpecialistPoolServiceClient({fallback: 'rest'}, gax);
+   *     const client = new SpecialistPoolServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -183,7 +182,7 @@ export class SpecialistPoolServiceClient {
     }
     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) {
@@ -342,7 +341,7 @@ export class SpecialistPoolServiceClient {
       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-aiplatform/src/v1beta1/tensorboard_service_client.ts b/packages/google-cloud-aiplatform/src/v1beta1/tensorboard_service_client.ts
index 270044e1086..ac0fc6e3c45 100644
--- a/packages/google-cloud-aiplatform/src/v1beta1/tensorboard_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1beta1/tensorboard_service_client.ts
@@ -99,8 +99,7 @@ export class TensorboardServiceClient {
    *     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 TensorboardServiceClient {
    *     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 TensorboardServiceClient({fallback: 'rest'}, gax);
+   *     const client = new TensorboardServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class TensorboardServiceClient {
     }
     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) {
@@ -356,7 +355,7 @@ export class TensorboardServiceClient {
     this.descriptors.stream = {
       readTensorboardBlobData: new this._gaxModule.StreamDescriptor(
         this._gaxModule.StreamType.SERVER_STREAMING,
-        opts.fallback === 'rest'
+        !!opts.fallback
       ),
     };
 
@@ -368,7 +367,7 @@ export class TensorboardServiceClient {
       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-aiplatform/src/v1beta1/vizier_service_client.ts b/packages/google-cloud-aiplatform/src/v1beta1/vizier_service_client.ts
index 92daf981520..a913e8d07ad 100644
--- a/packages/google-cloud-aiplatform/src/v1beta1/vizier_service_client.ts
+++ b/packages/google-cloud-aiplatform/src/v1beta1/vizier_service_client.ts
@@ -103,8 +103,7 @@ export class VizierServiceClient {
    *     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
@@ -112,7 +111,7 @@ export class VizierServiceClient {
    *     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 VizierServiceClient({fallback: 'rest'}, gax);
+   *     const client = new VizierServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -181,7 +180,7 @@ export class VizierServiceClient {
     }
     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) {
@@ -345,7 +344,7 @@ export class VizierServiceClient {
       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-alloydb/samples/quickstart.js b/packages/google-cloud-alloydb/samples/quickstart.js
index e59a8a6871c..559db016c85 100644
--- a/packages/google-cloud-alloydb/samples/quickstart.js
+++ b/packages/google-cloud-alloydb/samples/quickstart.js
@@ -58,8 +58,9 @@ function main(parent) {
     };
 
     // Run request
-    const iterable =
-      await alloydbClient.listSupportedDatabaseFlagsAsync(request);
+    const iterable = await alloydbClient.listSupportedDatabaseFlagsAsync(
+      request
+    );
     for await (const response of iterable) {
       console.log(response);
     }
diff --git a/packages/google-cloud-alloydb/src/v1/alloy_d_b_admin_client.ts b/packages/google-cloud-alloydb/src/v1/alloy_d_b_admin_client.ts
index d5dd3de90bc..ed485f60a86 100644
--- a/packages/google-cloud-alloydb/src/v1/alloy_d_b_admin_client.ts
+++ b/packages/google-cloud-alloydb/src/v1/alloy_d_b_admin_client.ts
@@ -99,8 +99,7 @@ export class AlloyDBAdminClient {
    *     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 AlloyDBAdminClient {
    *     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 AlloyDBAdminClient({fallback: 'rest'}, gax);
+   *     const client = new AlloyDBAdminClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -180,7 +179,7 @@ export class AlloyDBAdminClient {
     }
     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) {
@@ -255,7 +254,7 @@ export class AlloyDBAdminClient {
       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-alloydb/src/v1alpha/alloy_d_b_admin_client.ts b/packages/google-cloud-alloydb/src/v1alpha/alloy_d_b_admin_client.ts
index 7c439b4e9f4..67586dd5fe1 100644
--- a/packages/google-cloud-alloydb/src/v1alpha/alloy_d_b_admin_client.ts
+++ b/packages/google-cloud-alloydb/src/v1alpha/alloy_d_b_admin_client.ts
@@ -99,8 +99,7 @@ export class AlloyDBAdminClient {
    *     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 AlloyDBAdminClient {
    *     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 AlloyDBAdminClient({fallback: 'rest'}, gax);
+   *     const client = new AlloyDBAdminClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -180,7 +179,7 @@ export class AlloyDBAdminClient {
     }
     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) {
@@ -258,7 +257,7 @@ export class AlloyDBAdminClient {
       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-alloydb/src/v1beta/alloy_d_b_admin_client.ts b/packages/google-cloud-alloydb/src/v1beta/alloy_d_b_admin_client.ts
index d75b7d9b185..a7eff7d6eda 100644
--- a/packages/google-cloud-alloydb/src/v1beta/alloy_d_b_admin_client.ts
+++ b/packages/google-cloud-alloydb/src/v1beta/alloy_d_b_admin_client.ts
@@ -99,8 +99,7 @@ export class AlloyDBAdminClient {
    *     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 AlloyDBAdminClient {
    *     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 AlloyDBAdminClient({fallback: 'rest'}, gax);
+   *     const client = new AlloyDBAdminClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -180,7 +179,7 @@ export class AlloyDBAdminClient {
     }
     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) {
@@ -258,7 +257,7 @@ export class AlloyDBAdminClient {
       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-apigateway/src/v1/api_gateway_service_client.ts b/packages/google-cloud-apigateway/src/v1/api_gateway_service_client.ts
index a593b2f3db7..d9b3ac8977d 100644
--- a/packages/google-cloud-apigateway/src/v1/api_gateway_service_client.ts
+++ b/packages/google-cloud-apigateway/src/v1/api_gateway_service_client.ts
@@ -93,8 +93,7 @@ export class ApiGatewayServiceClient {
    *     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 ApiGatewayServiceClient {
    *     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 ApiGatewayServiceClient({fallback: 'rest'}, gax);
+   *     const client = new ApiGatewayServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -168,7 +167,7 @@ export class ApiGatewayServiceClient {
     }
     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 ApiGatewayServiceClient {
       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-apigeeconnect/src/v1/connection_service_client.ts b/packages/google-cloud-apigeeconnect/src/v1/connection_service_client.ts
index c5bdd351612..8b684bdb03d 100644
--- a/packages/google-cloud-apigeeconnect/src/v1/connection_service_client.ts
+++ b/packages/google-cloud-apigeeconnect/src/v1/connection_service_client.ts
@@ -90,8 +90,7 @@ export class ConnectionServiceClient {
    *     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 ConnectionServiceClient {
    *     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 ConnectionServiceClient({fallback: 'rest'}, gax);
+   *     const client = new ConnectionServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -165,7 +164,7 @@ export class ConnectionServiceClient {
     }
     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-apigeeconnect/src/v1/tether_client.ts b/packages/google-cloud-apigeeconnect/src/v1/tether_client.ts
index 70d7678b4a5..848d80f957c 100644
--- a/packages/google-cloud-apigeeconnect/src/v1/tether_client.ts
+++ b/packages/google-cloud-apigeeconnect/src/v1/tether_client.ts
@@ -89,8 +89,7 @@ export class TetherClient {
    *     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 TetherClient {
    *     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 TetherClient({fallback: 'rest'}, gax);
+   *     const client = new TetherClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -164,7 +163,7 @@ export class TetherClient {
     }
     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) {
@@ -178,7 +177,7 @@ export class TetherClient {
     this.descriptors.stream = {
       egress: new this._gaxModule.StreamDescriptor(
         this._gaxModule.StreamType.BIDI_STREAMING,
-        opts.fallback === 'rest'
+        !!opts.fallback
       ),
     };
 
diff --git a/packages/google-cloud-asset/src/v1/asset_service_client.ts b/packages/google-cloud-asset/src/v1/asset_service_client.ts
index d4aae8a0041..e18062340ea 100644
--- a/packages/google-cloud-asset/src/v1/asset_service_client.ts
+++ b/packages/google-cloud-asset/src/v1/asset_service_client.ts
@@ -93,8 +93,7 @@ export class AssetServiceClient {
    *     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 AssetServiceClient {
    *     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 AssetServiceClient({fallback: 'rest'}, gax);
+   *     const client = new AssetServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -168,7 +167,7 @@ export class AssetServiceClient {
     }
     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) {
@@ -265,7 +264,7 @@ export class AssetServiceClient {
       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-asset/src/v1p1beta1/asset_service_client.ts b/packages/google-cloud-asset/src/v1p1beta1/asset_service_client.ts
index 594ebff3131..bf873cd4c6b 100644
--- a/packages/google-cloud-asset/src/v1p1beta1/asset_service_client.ts
+++ b/packages/google-cloud-asset/src/v1p1beta1/asset_service_client.ts
@@ -89,8 +89,7 @@ export class AssetServiceClient {
    *     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 AssetServiceClient {
    *     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 AssetServiceClient({fallback: 'rest'}, gax);
+   *     const client = new AssetServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -164,7 +163,7 @@ export class AssetServiceClient {
     }
     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-asset/src/v1p2beta1/asset_service_client.ts b/packages/google-cloud-asset/src/v1p2beta1/asset_service_client.ts
index 149ae3af18a..7bb7e3cc160 100644
--- a/packages/google-cloud-asset/src/v1p2beta1/asset_service_client.ts
+++ b/packages/google-cloud-asset/src/v1p2beta1/asset_service_client.ts
@@ -88,8 +88,7 @@ export class AssetServiceClient {
    *     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 AssetServiceClient {
    *     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 AssetServiceClient({fallback: 'rest'}, gax);
+   *     const client = new AssetServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -163,7 +162,7 @@ export class AssetServiceClient {
     }
     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-asset/src/v1p5beta1/asset_service_client.ts b/packages/google-cloud-asset/src/v1p5beta1/asset_service_client.ts
index 314d26a7f6d..b6cee7ce2d4 100644
--- a/packages/google-cloud-asset/src/v1p5beta1/asset_service_client.ts
+++ b/packages/google-cloud-asset/src/v1p5beta1/asset_service_client.ts
@@ -90,8 +90,7 @@ export class AssetServiceClient {
    *     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 AssetServiceClient {
    *     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 AssetServiceClient({fallback: 'rest'}, gax);
+   *     const client = new AssetServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -165,7 +164,7 @@ export class AssetServiceClient {
     }
     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-asset/src/v1p7beta1/asset_service_client.ts b/packages/google-cloud-asset/src/v1p7beta1/asset_service_client.ts
index b6a5e513f49..4272cfa58b4 100644
--- a/packages/google-cloud-asset/src/v1p7beta1/asset_service_client.ts
+++ b/packages/google-cloud-asset/src/v1p7beta1/asset_service_client.ts
@@ -91,8 +91,7 @@ export class AssetServiceClient {
    *     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 AssetServiceClient {
    *     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 AssetServiceClient({fallback: 'rest'}, gax);
+   *     const client = new AssetServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -166,7 +165,7 @@ export class AssetServiceClient {
     }
     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 AssetServiceClient {
       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-asset/test/gapic_asset_service_v1.ts b/packages/google-cloud-asset/test/gapic_asset_service_v1.ts
index e7face67f14..ac066d79cf3 100644
--- a/packages/google-cloud-asset/test/gapic_asset_service_v1.ts
+++ b/packages/google-cloud-asset/test/gapic_asset_service_v1.ts
@@ -4116,8 +4116,9 @@ describe('v1.AssetServiceClient', () => {
       ];
       client.innerApiCalls.analyzeOrgPolicyGovernedContainers =
         stubSimpleCall(expectedResponse);
-      const [response] =
-        await client.analyzeOrgPolicyGovernedContainers(request);
+      const [response] = await client.analyzeOrgPolicyGovernedContainers(
+        request
+      );
       assert.deepStrictEqual(response, expectedResponse);
       const actualRequest = (
         client.innerApiCalls.analyzeOrgPolicyGovernedContainers as SinonStub
diff --git a/packages/google-cloud-assuredworkloads/src/v1/assured_workloads_service_client.ts b/packages/google-cloud-assuredworkloads/src/v1/assured_workloads_service_client.ts
index 5d7d6bdcf4e..d61dfc5bbd7 100644
--- a/packages/google-cloud-assuredworkloads/src/v1/assured_workloads_service_client.ts
+++ b/packages/google-cloud-assuredworkloads/src/v1/assured_workloads_service_client.ts
@@ -93,8 +93,7 @@ export class AssuredWorkloadsServiceClient {
    *     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 AssuredWorkloadsServiceClient {
    *     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 AssuredWorkloadsServiceClient({fallback: 'rest'}, gax);
+   *     const client = new AssuredWorkloadsServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -169,7 +168,7 @@ export class AssuredWorkloadsServiceClient {
     }
     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 AssuredWorkloadsServiceClient {
       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-assuredworkloads/src/v1beta1/assured_workloads_service_client.ts b/packages/google-cloud-assuredworkloads/src/v1beta1/assured_workloads_service_client.ts
index ba9bc8a8011..9b45325b45c 100644
--- a/packages/google-cloud-assuredworkloads/src/v1beta1/assured_workloads_service_client.ts
+++ b/packages/google-cloud-assuredworkloads/src/v1beta1/assured_workloads_service_client.ts
@@ -93,8 +93,7 @@ export class AssuredWorkloadsServiceClient {
    *     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 AssuredWorkloadsServiceClient {
    *     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 AssuredWorkloadsServiceClient({fallback: 'rest'}, gax);
+   *     const client = new AssuredWorkloadsServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -169,7 +168,7 @@ export class AssuredWorkloadsServiceClient {
     }
     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) {
@@ -206,7 +205,7 @@ export class AssuredWorkloadsServiceClient {
       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-baremetalsolution/src/v2/bare_metal_solution_client.ts b/packages/google-cloud-baremetalsolution/src/v2/bare_metal_solution_client.ts
index e453766363c..31211d7e915 100644
--- a/packages/google-cloud-baremetalsolution/src/v2/bare_metal_solution_client.ts
+++ b/packages/google-cloud-baremetalsolution/src/v2/bare_metal_solution_client.ts
@@ -106,8 +106,7 @@ export class BareMetalSolutionClient {
    *     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 BareMetalSolutionClient {
    *     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 BareMetalSolutionClient({fallback: 'rest'}, gax);
+   *     const client = new BareMetalSolutionClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -187,7 +186,7 @@ export class BareMetalSolutionClient {
     }
     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) {
@@ -306,7 +305,7 @@ export class BareMetalSolutionClient {
       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-batch/src/v1/batch_service_client.ts b/packages/google-cloud-batch/src/v1/batch_service_client.ts
index a4061576afb..20cddd550ff 100644
--- a/packages/google-cloud-batch/src/v1/batch_service_client.ts
+++ b/packages/google-cloud-batch/src/v1/batch_service_client.ts
@@ -98,8 +98,7 @@ export class BatchServiceClient {
    *     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 BatchServiceClient {
    *     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 BatchServiceClient({fallback: 'rest'}, gax);
+   *     const client = new BatchServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class BatchServiceClient {
     }
     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) {
@@ -231,7 +230,7 @@ export class BatchServiceClient {
       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-batch/src/v1alpha/batch_service_client.ts b/packages/google-cloud-batch/src/v1alpha/batch_service_client.ts
index 868f4fde84b..43d260a7363 100644
--- a/packages/google-cloud-batch/src/v1alpha/batch_service_client.ts
+++ b/packages/google-cloud-batch/src/v1alpha/batch_service_client.ts
@@ -98,8 +98,7 @@ export class BatchServiceClient {
    *     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 BatchServiceClient {
    *     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 BatchServiceClient({fallback: 'rest'}, gax);
+   *     const client = new BatchServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class BatchServiceClient {
     }
     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) {
@@ -231,7 +230,7 @@ export class BatchServiceClient {
       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-beyondcorp-appconnections/samples/quickstart.js b/packages/google-cloud-beyondcorp-appconnections/samples/quickstart.js
index c678c7794d1..c41b0ca36ed 100644
--- a/packages/google-cloud-beyondcorp-appconnections/samples/quickstart.js
+++ b/packages/google-cloud-beyondcorp-appconnections/samples/quickstart.js
@@ -68,8 +68,9 @@ function main(parent) {
     };
 
     // Run request
-    const iterable =
-      await appconnectionsClient.listAppConnectionsAsync(request);
+    const iterable = await appconnectionsClient.listAppConnectionsAsync(
+      request
+    );
     for await (const response of iterable) {
       console.log(response);
     }
diff --git a/packages/google-cloud-beyondcorp-appconnections/src/v1/app_connections_service_client.ts b/packages/google-cloud-beyondcorp-appconnections/src/v1/app_connections_service_client.ts
index 602a51b33b7..ce739014346 100644
--- a/packages/google-cloud-beyondcorp-appconnections/src/v1/app_connections_service_client.ts
+++ b/packages/google-cloud-beyondcorp-appconnections/src/v1/app_connections_service_client.ts
@@ -112,8 +112,7 @@ export class AppConnectionsServiceClient {
    *     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
@@ -121,7 +120,7 @@ export class AppConnectionsServiceClient {
    *     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 AppConnectionsServiceClient({fallback: 'rest'}, gax);
+   *     const client = new AppConnectionsServiceClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -194,7 +193,7 @@ export class AppConnectionsServiceClient {
     }
     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) {
@@ -245,7 +244,7 @@ export class AppConnectionsServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {