diff --git a/src/v1/auto_ml_client.ts b/src/v1/auto_ml_client.ts
index a40ced02..5c794103 100644
--- a/src/v1/auto_ml_client.ts
+++ b/src/v1/auto_ml_client.ts
@@ -106,8 +106,7 @@ export class AutoMlClient {
    *     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 AutoMlClient {
    *     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 AutoMlClient({fallback: 'rest'}, gax);
+   *     const client = new AutoMlClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -181,7 +180,7 @@ export class AutoMlClient {
     }
     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) {
@@ -240,7 +239,7 @@ export class AutoMlClient {
       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/src/v1/prediction_service_client.ts b/src/v1/prediction_service_client.ts
index df84e16b..88ff607a 100644
--- a/src/v1/prediction_service_client.ts
+++ b/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(
@@ -169,7 +168,7 @@ 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) {
@@ -204,7 +203,7 @@ export class PredictionServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {
diff --git a/src/v1beta1/auto_ml_client.ts b/src/v1beta1/auto_ml_client.ts
index 47f66bd7..99c19bcd 100644
--- a/src/v1beta1/auto_ml_client.ts
+++ b/src/v1beta1/auto_ml_client.ts
@@ -106,8 +106,7 @@ export class AutoMlClient {
    *     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 AutoMlClient {
    *     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 AutoMlClient({fallback: 'rest'}, gax);
+   *     const client = new AutoMlClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -181,7 +180,7 @@ export class AutoMlClient {
     }
     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) {
@@ -256,7 +255,7 @@ export class AutoMlClient {
       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/src/v1beta1/prediction_service_client.ts b/src/v1beta1/prediction_service_client.ts
index 2df46725..86c19c5f 100644
--- a/src/v1beta1/prediction_service_client.ts
+++ b/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(
@@ -169,7 +168,7 @@ 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) {
@@ -210,7 +209,7 @@ export class PredictionServiceClient {
       auth: this.auth,
       grpc: 'grpc' in this._gaxGrpc ? this._gaxGrpc.grpc : undefined,
     };
-    if (opts.fallback === 'rest') {
+    if (opts.fallback) {
       lroOptions.protoJson = protoFilesRoot;
       lroOptions.httpRules = [
         {