diff --git a/src/v4/company_service_client.ts b/src/v4/company_service_client.ts
index 87852c2..1b6a20e 100644
--- a/src/v4/company_service_client.ts
+++ b/src/v4/company_service_client.ts
@@ -140,6 +140,8 @@ export class CompanyServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
+    } else if (opts.fallback === 'rest') {
+      clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
       clientHeader.push(`${opts.libName}/${opts.libVersion}`);
diff --git a/src/v4/completion_client.ts b/src/v4/completion_client.ts
index 4dd88ad..cf5afdd 100644
--- a/src/v4/completion_client.ts
+++ b/src/v4/completion_client.ts
@@ -131,6 +131,8 @@ export class CompletionClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
+    } else if (opts.fallback === 'rest') {
+      clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
       clientHeader.push(`${opts.libName}/${opts.libVersion}`);
diff --git a/src/v4/event_service_client.ts b/src/v4/event_service_client.ts
index a04daec..c7e5210 100644
--- a/src/v4/event_service_client.ts
+++ b/src/v4/event_service_client.ts
@@ -131,6 +131,8 @@ export class EventServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
+    } else if (opts.fallback === 'rest') {
+      clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
       clientHeader.push(`${opts.libName}/${opts.libVersion}`);
diff --git a/src/v4/job_service_client.ts b/src/v4/job_service_client.ts
index bbc7070..22ae562 100644
--- a/src/v4/job_service_client.ts
+++ b/src/v4/job_service_client.ts
@@ -142,6 +142,8 @@ export class JobServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
+    } else if (opts.fallback === 'rest') {
+      clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
       clientHeader.push(`${opts.libName}/${opts.libVersion}`);
diff --git a/src/v4/tenant_service_client.ts b/src/v4/tenant_service_client.ts
index f74b821..c960f2b 100644
--- a/src/v4/tenant_service_client.ts
+++ b/src/v4/tenant_service_client.ts
@@ -140,6 +140,8 @@ export class TenantServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
+    } else if (opts.fallback === 'rest') {
+      clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
       clientHeader.push(`${opts.libName}/${opts.libVersion}`);
diff --git a/src/v4beta1/application_service_client.ts b/src/v4beta1/application_service_client.ts
index 8730307..da8c7db 100644
--- a/src/v4beta1/application_service_client.ts
+++ b/src/v4beta1/application_service_client.ts
@@ -141,6 +141,8 @@ export class ApplicationServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
+    } else if (opts.fallback === 'rest') {
+      clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
       clientHeader.push(`${opts.libName}/${opts.libVersion}`);
diff --git a/src/v4beta1/company_service_client.ts b/src/v4beta1/company_service_client.ts
index b23c1da..d0646e7 100644
--- a/src/v4beta1/company_service_client.ts
+++ b/src/v4beta1/company_service_client.ts
@@ -140,6 +140,8 @@ export class CompanyServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
+    } else if (opts.fallback === 'rest') {
+      clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
       clientHeader.push(`${opts.libName}/${opts.libVersion}`);
diff --git a/src/v4beta1/completion_client.ts b/src/v4beta1/completion_client.ts
index f0abf82..adac5fe 100644
--- a/src/v4beta1/completion_client.ts
+++ b/src/v4beta1/completion_client.ts
@@ -131,6 +131,8 @@ export class CompletionClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
+    } else if (opts.fallback === 'rest') {
+      clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
       clientHeader.push(`${opts.libName}/${opts.libVersion}`);
diff --git a/src/v4beta1/event_service_client.ts b/src/v4beta1/event_service_client.ts
index fb00873..f5981c9 100644
--- a/src/v4beta1/event_service_client.ts
+++ b/src/v4beta1/event_service_client.ts
@@ -131,6 +131,8 @@ export class EventServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
+    } else if (opts.fallback === 'rest') {
+      clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
       clientHeader.push(`${opts.libName}/${opts.libVersion}`);
diff --git a/src/v4beta1/job_service_client.ts b/src/v4beta1/job_service_client.ts
index de46d5c..52d25b8 100644
--- a/src/v4beta1/job_service_client.ts
+++ b/src/v4beta1/job_service_client.ts
@@ -142,6 +142,8 @@ export class JobServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
+    } else if (opts.fallback === 'rest') {
+      clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
       clientHeader.push(`${opts.libName}/${opts.libVersion}`);
diff --git a/src/v4beta1/profile_service_client.ts b/src/v4beta1/profile_service_client.ts
index 070afe0..ac676e9 100644
--- a/src/v4beta1/profile_service_client.ts
+++ b/src/v4beta1/profile_service_client.ts
@@ -141,6 +141,8 @@ export class ProfileServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
+    } else if (opts.fallback === 'rest') {
+      clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
       clientHeader.push(`${opts.libName}/${opts.libVersion}`);
diff --git a/src/v4beta1/tenant_service_client.ts b/src/v4beta1/tenant_service_client.ts
index a4e0052..cfc4ed7 100644
--- a/src/v4beta1/tenant_service_client.ts
+++ b/src/v4beta1/tenant_service_client.ts
@@ -140,6 +140,8 @@ export class TenantServiceClient {
     }
     if (!opts.fallback) {
       clientHeader.push(`grpc/${this._gaxGrpc.grpcVersion}`);
+    } else if (opts.fallback === 'rest') {
+      clientHeader.push(`rest/${this._gaxGrpc.grpcVersion}`);
     }
     if (opts.libName && opts.libVersion) {
       clientHeader.push(`${opts.libName}/${opts.libVersion}`);