diff --git a/src/v1/provisioning_client.ts b/src/v1/provisioning_client.ts
index 7fd22c4..c04c0a7 100644
--- a/src/v1/provisioning_client.ts
+++ b/src/v1/provisioning_client.ts
@@ -98,8 +98,7 @@ export class ProvisioningClient {
    *     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 ProvisioningClient {
    *     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 ProvisioningClient({fallback: 'rest'}, gax);
+   *     const client = new ProvisioningClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -179,7 +178,7 @@ export class ProvisioningClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
-    } else if (opts.fallback === 'rest') {
+    } else {
       clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
@@ -238,7 +237,7 @@ export class ProvisioningClient {
       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/registry_client.ts b/src/v1/registry_client.ts
index ff869c6..411181d 100644
--- a/src/v1/registry_client.ts
+++ b/src/v1/registry_client.ts
@@ -96,8 +96,7 @@ export class RegistryClient {
    *     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 RegistryClient {
    *     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 RegistryClient({fallback: 'rest'}, gax);
+   *     const client = new RegistryClient({fallback: true}, gax);
    *     ```
    */
   constructor(
@@ -177,7 +176,7 @@ export class RegistryClient {
     }
     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) {