diff --git a/modules/gke-cluster-autopilot/README.md b/modules/gke-cluster-autopilot/README.md
index 2ad1cf4b07..c4176a1df8 100644
--- a/modules/gke-cluster-autopilot/README.md
+++ b/modules/gke-cluster-autopilot/README.md
@@ -122,7 +122,7 @@ module "cluster-1" {
 | [location](variables.tf#L110) | Autopilot cluster are always regional. | <code>string</code> | ✓ |  |
 | [name](variables.tf#L155) | Cluster name. | <code>string</code> | ✓ |  |
 | [project_id](variables.tf#L181) | Cluster project id. | <code>string</code> | ✓ |  |
-| [vpc_config](variables.tf#L204) | VPC-level configuration. | <code title="object&#40;&#123;&#10;  network                &#61; string&#10;  subnetwork             &#61; string&#10;  master_ipv4_cidr_block &#61; optional&#40;string&#41;&#10;  secondary_range_blocks &#61; optional&#40;object&#40;&#123;&#10;    pods     &#61; string&#10;    services &#61; string&#10;  &#125;&#41;&#41;&#10;  secondary_range_names &#61; optional&#40;object&#40;&#123;&#10;    pods     &#61; string&#10;    services &#61; string&#10;  &#125;&#41;, &#123; pods &#61; &#34;pods&#34;, services &#61; &#34;services&#34; &#125;&#41;&#10;  master_authorized_ranges &#61; optional&#40;map&#40;string&#41;&#41;&#10;  stack_type               &#61; optional&#40;string&#41;&#10;&#125;&#41;">object&#40;&#123;&#8230;&#125;&#41;</code> | ✓ |  |
+| [vpc_config](variables.tf#L209) | VPC-level configuration. | <code title="object&#40;&#123;&#10;  network                &#61; string&#10;  subnetwork             &#61; string&#10;  master_ipv4_cidr_block &#61; optional&#40;string&#41;&#10;  secondary_range_blocks &#61; optional&#40;object&#40;&#123;&#10;    pods     &#61; string&#10;    services &#61; string&#10;  &#125;&#41;&#41;&#10;  secondary_range_names &#61; optional&#40;object&#40;&#123;&#10;    pods     &#61; string&#10;    services &#61; string&#10;  &#125;&#41;, &#123; pods &#61; &#34;pods&#34;, services &#61; &#34;services&#34; &#125;&#41;&#10;  master_authorized_ranges &#61; optional&#40;map&#40;string&#41;&#41;&#10;  stack_type               &#61; optional&#40;string&#41;&#10;&#125;&#41;">object&#40;&#123;&#8230;&#125;&#41;</code> | ✓ |  |
 | [backup_configs](variables.tf#L17) | Configuration for Backup for GKE. | <code title="object&#40;&#123;&#10;  enable_backup_agent &#61; optional&#40;bool, false&#41;&#10;  backup_plans &#61; optional&#40;map&#40;object&#40;&#123;&#10;    encryption_key                    &#61; optional&#40;string&#41;&#10;    include_secrets                   &#61; optional&#40;bool, true&#41;&#10;    include_volume_data               &#61; optional&#40;bool, true&#41;&#10;    namespaces                        &#61; optional&#40;list&#40;string&#41;&#41;&#10;    region                            &#61; string&#10;    schedule                          &#61; string&#10;    retention_policy_days             &#61; optional&#40;string&#41;&#10;    retention_policy_lock             &#61; optional&#40;bool, false&#41;&#10;    retention_policy_delete_lock_days &#61; optional&#40;string&#41;&#10;  &#125;&#41;&#41;, &#123;&#125;&#41;&#10;&#125;&#41;">object&#40;&#123;&#8230;&#125;&#41;</code> |  | <code>&#123;&#125;</code> |
 | [description](variables.tf#L37) | Cluster description. | <code>string</code> |  | <code>null</code> |
 | [enable_addons](variables.tf#L43) | Addons enabled in the cluster (true means enabled). | <code title="object&#40;&#123;&#10;  cloudrun                   &#61; optional&#40;bool, false&#41;&#10;  config_connector           &#61; optional&#40;bool, false&#41;&#10;  dns_cache                  &#61; optional&#40;bool, false&#41;&#10;  horizontal_pod_autoscaling &#61; optional&#40;bool, false&#41;&#10;  http_load_balancing        &#61; optional&#40;bool, false&#41;&#10;  istio &#61; optional&#40;object&#40;&#123;&#10;    enable_tls &#61; bool&#10;  &#125;&#41;&#41;&#10;  kalm           &#61; optional&#40;bool, false&#41;&#10;  network_policy &#61; optional&#40;bool, false&#41;&#10;&#125;&#41;">object&#40;&#123;&#8230;&#125;&#41;</code> |  | <code title="&#123;&#10;  horizontal_pod_autoscaling &#61; true&#10;  http_load_balancing        &#61; true&#10;&#125;">&#123;&#8230;&#125;</code> |
@@ -134,9 +134,9 @@ module "cluster-1" {
 | [min_master_version](variables.tf#L149) | Minimum version of the master, defaults to the version of the most recent official release. | <code>string</code> |  | <code>null</code> |
 | [node_locations](variables.tf#L160) | Zones in which the cluster's nodes are located. | <code>list&#40;string&#41;</code> |  | <code>&#91;&#93;</code> |
 | [private_cluster_config](variables.tf#L167) | Private cluster configuration. | <code title="object&#40;&#123;&#10;  enable_private_endpoint &#61; optional&#40;bool&#41;&#10;  master_global_access    &#61; optional&#40;bool&#41;&#10;  peering_config &#61; optional&#40;object&#40;&#123;&#10;    export_routes &#61; optional&#40;bool&#41;&#10;    import_routes &#61; optional&#40;bool&#41;&#10;    project_id    &#61; optional&#40;string&#41;&#10;  &#125;&#41;&#41;&#10;&#125;&#41;">object&#40;&#123;&#8230;&#125;&#41;</code> |  | <code>null</code> |
-| [release_channel](variables.tf#L186) | Release channel for GKE upgrades. | <code>string</code> |  | <code>null</code> |
-| [service_account](variables.tf#L192) | The Google Cloud Platform Service Account to be used by the node VMs created by GKE Autopilot. | <code>string</code> |  | <code>null</code> |
-| [tags](variables.tf#L198) | Network tags applied to nodes. | <code>list&#40;string&#41;</code> |  | <code>null</code> |
+| [release_channel](variables.tf#L186) | Release channel for GKE upgrades. Clusters created in the Autopilot mode must use a release channel. Choose between \"RAPID\", \"REGULAR\", and \"STABLE\". | <code>string</code> |  | <code>&#34;REGULAR&#34;</code> |
+| [service_account](variables.tf#L197) | The Google Cloud Platform Service Account to be used by the node VMs created by GKE Autopilot. | <code>string</code> |  | <code>null</code> |
+| [tags](variables.tf#L203) | Network tags applied to nodes. | <code>list&#40;string&#41;</code> |  | <code>null</code> |
 
 ## Outputs
 
diff --git a/modules/gke-cluster-autopilot/main.tf b/modules/gke-cluster-autopilot/main.tf
index d5826b8591..7ae4d04490 100644
--- a/modules/gke-cluster-autopilot/main.tf
+++ b/modules/gke-cluster-autopilot/main.tf
@@ -238,11 +238,8 @@ resource "google_container_cluster" "cluster" {
     }
   }
 
-  dynamic "release_channel" {
-    for_each = var.release_channel != null ? [""] : []
-    content {
-      channel = var.release_channel
-    }
+  release_channel {
+    channel = var.release_channel
   }
 
   dynamic "resource_usage_export_config" {
diff --git a/modules/gke-cluster-autopilot/variables.tf b/modules/gke-cluster-autopilot/variables.tf
index c4aa1f93e8..9a30b5bf3e 100644
--- a/modules/gke-cluster-autopilot/variables.tf
+++ b/modules/gke-cluster-autopilot/variables.tf
@@ -184,9 +184,14 @@ variable "project_id" {
 }
 
 variable "release_channel" {
-  description = "Release channel for GKE upgrades."
+  description = "Release channel for GKE upgrades. Clusters created in the Autopilot mode must use a release channel. Choose between \"RAPID\", \"REGULAR\", and \"STABLE\"."
   type        = string
-  default     = null
+  default     = "REGULAR"
+  nullable    = false
+  validation {
+    condition     = contains(["RAPID", "REGULAR", "STABLE"], var.release_channel)
+    error_message = "Must be one of: RAPID, REGULAR, STABLE."
+  }
 }
 
 variable "service_account" {