diff --git a/gcp/pubsub/src/main/scala/com/commercetools/queue/gcp/pubsub/PubSubClient.scala b/gcp/pubsub/src/main/scala/com/commercetools/queue/gcp/pubsub/PubSubClient.scala
index b4eac2e..252d586 100644
--- a/gcp/pubsub/src/main/scala/com/commercetools/queue/gcp/pubsub/PubSubClient.scala
+++ b/gcp/pubsub/src/main/scala/com/commercetools/queue/gcp/pubsub/PubSubClient.scala
@@ -20,12 +20,13 @@ import cats.effect.{Async, Resource}
 import com.commercetools.queue.{Deserializer, QueueAdministration, QueueClient, QueuePublisher, QueueSubscriber, Serializer}
 import com.google.api.gax.core.CredentialsProvider
 import com.google.api.gax.httpjson.{HttpJsonTransportChannel, ManagedHttpJsonChannel}
-import com.google.api.gax.rpc.{FixedTransportChannelProvider, TransportChannel, TransportChannelProvider}
+import com.google.api.gax.rpc.{FixedTransportChannelProvider, TransportChannelProvider}
 import com.google.pubsub.v1.{SubscriptionName, TopicName}
 
 class PubSubClient[F[_]: Async] private (
   project: String,
   channelProvider: TransportChannelProvider,
+  useGrpc: Boolean,
   credentials: CredentialsProvider,
   endpoint: Option[String])
   extends QueueClient[F] {
@@ -39,6 +40,7 @@ class PubSubClient[F[_]: Async] private (
   override def subscribe[T: Deserializer](name: String): QueueSubscriber[F, T] =
     new PubSubSubscriber[F, T](
       name,
+      useGrpc,
       SubscriptionName.of(project, s"fs2-queue-$name"),
       channelProvider,
       credentials,
@@ -48,7 +50,7 @@ class PubSubClient[F[_]: Async] private (
 
 object PubSubClient {
 
-  private def makeDefaultTransportChannel(endpoint: Option[String]): TransportChannel =
+  private def makeDefaultTransportChannel(endpoint: Option[String]): HttpJsonTransportChannel =
     HttpJsonTransportChannel.create(
       ManagedHttpJsonChannel.newBuilder().setEndpoint(endpoint.getOrElse("https://pubsub.googleapis.com")).build())
 
@@ -56,13 +58,23 @@ object PubSubClient {
     project: String,
     credentials: CredentialsProvider,
     endpoint: Option[String] = None,
-    mkTransportChannel: Option[String] => TransportChannel = makeDefaultTransportChannel _
+    mkTransportChannel: Option[String] => HttpJsonTransportChannel = makeDefaultTransportChannel _
   )(implicit F: Async[F]
   ): Resource[F, PubSubClient[F]] =
     Resource
       .fromAutoCloseable(F.blocking(mkTransportChannel(endpoint)))
       .map { channel =>
-        new PubSubClient[F](project, FixedTransportChannelProvider.create(channel), credentials, endpoint)
+        new PubSubClient[F](project, FixedTransportChannelProvider.create(channel), false, credentials, endpoint)
       }
 
+  def unmanaged[F[_]](
+    project: String,
+    credentials: CredentialsProvider,
+    channelProvider: TransportChannelProvider,
+    useGrpc: Boolean,
+    endpoint: Option[String] = None
+  )(implicit F: Async[F]
+  ): PubSubClient[F] =
+    new PubSubClient[F](project, channelProvider, useGrpc, credentials, endpoint)
+
 }
diff --git a/gcp/pubsub/src/main/scala/com/commercetools/queue/gcp/pubsub/PubSubPuller.scala b/gcp/pubsub/src/main/scala/com/commercetools/queue/gcp/pubsub/PubSubPuller.scala
index f16c899..c4b035c 100644
--- a/gcp/pubsub/src/main/scala/com/commercetools/queue/gcp/pubsub/PubSubPuller.scala
+++ b/gcp/pubsub/src/main/scala/com/commercetools/queue/gcp/pubsub/PubSubPuller.scala
@@ -20,9 +20,10 @@ import cats.effect.Async
 import cats.effect.syntax.concurrent._
 import cats.syntax.all._
 import com.commercetools.queue.{Deserializer, MessageContext, QueuePuller}
+import com.google.api.gax.grpc.GrpcCallContext
 import com.google.api.gax.httpjson.HttpJsonCallContext
 import com.google.api.gax.retrying.RetrySettings
-import com.google.api.gax.rpc.DeadlineExceededException
+import com.google.api.gax.rpc.{ApiCallContext, DeadlineExceededException}
 import com.google.cloud.pubsub.v1.stub.SubscriberStub
 import com.google.pubsub.v1.{ModifyAckDeadlineRequest, PullRequest, ReceivedMessage, SubscriptionName}
 import fs2.Chunk
@@ -34,6 +35,7 @@ import scala.jdk.CollectionConverters._
 
 class PubSubPuller[F[_], T](
   val queueName: String,
+  useGrpc: Boolean,
   subscriptionName: SubscriptionName,
   subscriber: SubscriberStub,
   lockTTLSeconds: Int
@@ -42,15 +44,23 @@ class PubSubPuller[F[_], T](
   deserializer: Deserializer[T])
   extends QueuePuller[F, T] {
 
+  private def callContext(waitingTime: FiniteDuration): ApiCallContext =
+    if (useGrpc)
+      GrpcCallContext
+        .createDefault()
+        .withRetrySettings(
+          RetrySettings.newBuilder().setLogicalTimeout(Duration.ofMillis(waitingTime.toMillis)).build())
+    else
+      HttpJsonCallContext
+        .createDefault()
+        .withRetrySettings(
+          RetrySettings.newBuilder().setLogicalTimeout(Duration.ofMillis(waitingTime.toMillis)).build())
+
   override def pullBatch(batchSize: Int, waitingTime: FiniteDuration): F[Chunk[MessageContext[F, T]]] =
     wrapFuture(F.delay {
       subscriber
         .pullCallable()
-        .withDefaultCallContext(
-          HttpJsonCallContext
-            .createDefault()
-            .withRetrySettings(
-              RetrySettings.newBuilder().setLogicalTimeout(Duration.ofMillis(waitingTime.toMillis)).build()))
+        .withDefaultCallContext(callContext(waitingTime))
         .futureCall(
           PullRequest.newBuilder().setMaxMessages(batchSize).setSubscription(subscriptionName.toString()).build())
     }).map(response => Chunk.from(response.getReceivedMessagesList().asScala))
@@ -59,6 +69,16 @@ class PubSubPuller[F[_], T](
         Chunk.empty
       }
       .flatMap { (msgs: Chunk[ReceivedMessage]) =>
+        // PubSub does not support delayed messages
+        // Instead in this case, we set a custom attribute when publishing
+        // with a delay. The attribute contains the earliest delivery date
+        // according to the delay.
+        // If the `Puller` gets a message with this attribute, we check wether
+        // it is in the future.
+        // If it is the case, the ack deadline is modified to be the amount of
+        // remaining seconds until this date.
+        // This way, the message will not be delivered until this expires.
+        // The message is ignored (filtered out of the batch)
         msgs.traverseFilter[F, ReceivedMessage] { msg =>
           val attrs = msg.getMessage().getAttributesMap().asScala
           F.realTimeInstant.flatMap { now =>
diff --git a/gcp/pubsub/src/main/scala/com/commercetools/queue/gcp/pubsub/PubSubSubscriber.scala b/gcp/pubsub/src/main/scala/com/commercetools/queue/gcp/pubsub/PubSubSubscriber.scala
index 6e665c0..e33842c 100644
--- a/gcp/pubsub/src/main/scala/com/commercetools/queue/gcp/pubsub/PubSubSubscriber.scala
+++ b/gcp/pubsub/src/main/scala/com/commercetools/queue/gcp/pubsub/PubSubSubscriber.scala
@@ -26,6 +26,7 @@ import com.google.pubsub.v1.{GetSubscriptionRequest, SubscriptionName}
 
 class PubSubSubscriber[F[_], T](
   val queueName: String,
+  useGrpc: Boolean,
   subscriptionName: SubscriptionName,
   channelProvider: TransportChannelProvider,
   credentials: CredentialsProvider,
@@ -56,7 +57,7 @@ class PubSubSubscriber[F[_], T](
           sub => (subscriber, sub))
       }
       .map { case (subscriber, subscription) =>
-        new PubSubPuller[F, T](queueName, subscriptionName, subscriber, subscription.getAckDeadlineSeconds())
+        new PubSubPuller[F, T](queueName, useGrpc, subscriptionName, subscriber, subscription.getAckDeadlineSeconds())
       }
 
 }