diff --git a/products/pubsub/api.yaml b/products/pubsub/api.yaml
index cb07dc42a139..d6e512f73eb2 100644
--- a/products/pubsub/api.yaml
+++ b/products/pubsub/api.yaml
@@ -144,3 +144,23 @@ objects:
 
           If the subscriber never acknowledges the message, the Pub/Sub system
           will eventually redeliver the message.
+      - !ruby/object:Api::Type::String
+        name: 'messageRetentionDuration'
+        default_value: '604800s'
+        description: |
+          How long to retain unacknowledged messages in the subscription's
+          backlog, from the moment a message is published. If
+          retainAckedMessages is true, then this also configures the retention
+          of acknowledged messages, and thus configures how far back in time a
+          subscriptions.seek can be done. Defaults to 7 days. Cannot be more
+          than 7 days (`"604800s"`) or less than 10 minutes (`"600s"`).
+
+          A duration in seconds with up to nine fractional digits, terminated
+          by 's'. Example: `"600.5s"`.
+      - !ruby/object:Api::Type::Boolean
+        name: 'retainAckedMessages'
+        description: |
+          Indicates whether to retain acknowledged messages. If `true`, then
+          messages are not expunged from the subscription's backlog, even if
+          they are acknowledged, until they fall out of the
+          messageRetentionDuration window.
diff --git a/templates/terraform/examples/pubsub_subscription_pull.tf.erb b/templates/terraform/examples/pubsub_subscription_pull.tf.erb
index d47fb9fa403a..91c1b38fbb6a 100644
--- a/templates/terraform/examples/pubsub_subscription_pull.tf.erb
+++ b/templates/terraform/examples/pubsub_subscription_pull.tf.erb
@@ -10,5 +10,9 @@ resource "google_pubsub_subscription" "<%= ctx[:primary_resource_id] %>" {
     foo = "bar"
   }
 
+  # 20 minutes
+  message_retention_duration = "1200s"
+  retain_acked_messages = true
+
   ack_deadline_seconds = 20
 }