diff --git a/.changelog/34985.txt b/.changelog/34985.txt
new file mode 100644
index 000000000000..7fa56e55928e
--- /dev/null
+++ b/.changelog/34985.txt
@@ -0,0 +1,7 @@
+```release-note:enhancement
+resource/aws_neptune_cluster: Add `storage_type` argument
+```
+
+```release-note:enhancement
+resource/aws_neptune_cluster_instance: Add `storage_type` attribute
+```
\ No newline at end of file
diff --git a/internal/service/neptune/cluster.go b/internal/service/neptune/cluster.go
index 580fba46575d..be2a4bf201a1 100644
--- a/internal/service/neptune/cluster.go
+++ b/internal/service/neptune/cluster.go
@@ -288,6 +288,20 @@ func ResourceCluster() *schema.Resource {
 				ForceNew: true,
 				Default:  false,
 			},
+			"storage_type": {
+				Type:     schema.TypeString,
+				Optional: true,
+				Computed: true,
+				DiffSuppressFunc: func(k, old, new string, d *schema.ResourceData) bool {
+					// https://docs.aws.amazon.com/neptune/latest/userguide/storage-types.html#provisioned-iops-storage:
+					// "You can determine whether a cluster is using I/O–Optimized storage using any describe- call. If the I/O–Optimized storage is enabled, the call returns a storage-type field set to iopt1".
+					if old == "" && new == storageTypeStandard {
+						return true
+					}
+					return new == old
+				},
+				ValidateFunc: validation.StringInSlice(storageType_Values(), false),
+			},
 			names.AttrTags:    tftags.TagsSchema(),
 			names.AttrTagsAll: tftags.TagsSchemaComputed(),
 			"vpc_security_group_ids": {
@@ -363,12 +377,6 @@ func resourceClusterCreate(ctx context.Context, d *schema.ResourceData, meta int
 		}
 	}
 
-	if v, ok := d.GetOk("global_cluster_identifier"); ok {
-		v := v.(string)
-
-		inputC.GlobalClusterIdentifier = aws.String(v)
-	}
-
 	if v, ok := d.GetOk("enable_cloudwatch_logs_exports"); ok && v.(*schema.Set).Len() > 0 {
 		v := v.(*schema.Set)
 
@@ -383,6 +391,12 @@ func resourceClusterCreate(ctx context.Context, d *schema.ResourceData, meta int
 		inputR.EngineVersion = aws.String(v)
 	}
 
+	if v, ok := d.GetOk("global_cluster_identifier"); ok {
+		v := v.(string)
+
+		inputC.GlobalClusterIdentifier = aws.String(v)
+	}
+
 	if v, ok := d.GetOk("iam_database_authentication_enabled"); ok {
 		v := v.(bool)
 
@@ -432,6 +446,13 @@ func resourceClusterCreate(ctx context.Context, d *schema.ResourceData, meta int
 		inputC.ReplicationSourceIdentifier = aws.String(v)
 	}
 
+	if v, ok := d.GetOk("storage_type"); ok {
+		v := v.(string)
+
+		inputC.StorageType = aws.String(v)
+		inputR.StorageType = aws.String(v)
+	}
+
 	if v, ok := d.GetOk("vpc_security_group_ids"); ok && v.(*schema.Set).Len() > 0 {
 		v := v.(*schema.Set)
 
@@ -549,6 +570,7 @@ func resourceClusterRead(ctx context.Context, d *schema.ResourceData, meta inter
 		return sdkdiag.AppendErrorf(diags, "setting serverless_v2_scaling_configuration: %s", err)
 	}
 	d.Set("storage_encrypted", dbc.StorageEncrypted)
+	d.Set("storage_type", dbc.StorageType)
 	var securityGroupIDs []string
 	for _, v := range dbc.VpcSecurityGroups {
 		securityGroupIDs = append(securityGroupIDs, aws.StringValue(v.VpcSecurityGroupId))
@@ -570,23 +592,16 @@ func resourceClusterUpdate(ctx context.Context, d *schema.ResourceData, meta int
 			DBClusterIdentifier:      aws.String(d.Id()),
 		}
 
-		if d.HasChange("copy_tags_to_snapshot") {
-			input.CopyTagsToSnapshot = aws.Bool(d.Get("copy_tags_to_snapshot").(bool))
+		if d.HasChange("backup_retention_period") {
+			input.BackupRetentionPeriod = aws.Int64(int64(d.Get("backup_retention_period").(int)))
 		}
 
-		// The DBInstanceParameterGroupName parameter is only valid in combination with the AllowMajorVersionUpgrade parameter.
-		if allowMajorVersionUpgrade {
-			if v, ok := d.GetOk("neptune_instance_parameter_group_name"); ok {
-				input.DBInstanceParameterGroupName = aws.String(v.(string))
-			}
+		if d.HasChange("copy_tags_to_snapshot") {
+			input.CopyTagsToSnapshot = aws.Bool(d.Get("copy_tags_to_snapshot").(bool))
 		}
 
-		if d.HasChange("vpc_security_group_ids") {
-			if v := d.Get("vpc_security_group_ids").(*schema.Set); v.Len() > 0 {
-				input.VpcSecurityGroupIds = flex.ExpandStringSet(v)
-			} else {
-				input.VpcSecurityGroupIds = aws.StringSlice([]string{})
-			}
+		if d.HasChange("deletion_protection") {
+			input.DeletionProtection = aws.Bool(d.Get("deletion_protection").(bool))
 		}
 
 		if d.HasChange("enable_cloudwatch_logs_exports") {
@@ -609,39 +624,50 @@ func resourceClusterUpdate(ctx context.Context, d *schema.ResourceData, meta int
 			input.CloudwatchLogsExportConfiguration = logs
 		}
 
-		if d.HasChange("preferred_backup_window") {
-			input.PreferredBackupWindow = aws.String(d.Get("preferred_backup_window").(string))
-		}
-
-		if d.HasChange("preferred_maintenance_window") {
-			input.PreferredMaintenanceWindow = aws.String(d.Get("preferred_maintenance_window").(string))
+		if d.HasChange("engine_version") {
+			input.EngineVersion = aws.String(d.Get("engine_version").(string))
+			input.DBClusterParameterGroupName = aws.String(d.Get("neptune_cluster_parameter_group_name").(string))
 		}
 
-		if d.HasChange("backup_retention_period") {
-			input.BackupRetentionPeriod = aws.Int64(int64(d.Get("backup_retention_period").(int)))
+		if d.HasChange("iam_database_authentication_enabled") {
+			input.EnableIAMDatabaseAuthentication = aws.Bool(d.Get("iam_database_authentication_enabled").(bool))
 		}
 
 		if d.HasChange("neptune_cluster_parameter_group_name") {
 			input.DBClusterParameterGroupName = aws.String(d.Get("neptune_cluster_parameter_group_name").(string))
 		}
 
-		if d.HasChange("iam_database_authentication_enabled") {
-			input.EnableIAMDatabaseAuthentication = aws.Bool(d.Get("iam_database_authentication_enabled").(bool))
+		// The DBInstanceParameterGroupName parameter is only valid in combination with the AllowMajorVersionUpgrade parameter.
+		if allowMajorVersionUpgrade {
+			if v, ok := d.GetOk("neptune_instance_parameter_group_name"); ok {
+				input.DBInstanceParameterGroupName = aws.String(v.(string))
+			}
 		}
 
-		if d.HasChange("deletion_protection") {
-			input.DeletionProtection = aws.Bool(d.Get("deletion_protection").(bool))
+		if d.HasChange("preferred_backup_window") {
+			input.PreferredBackupWindow = aws.String(d.Get("preferred_backup_window").(string))
 		}
 
-		if d.HasChange("engine_version") {
-			input.EngineVersion = aws.String(d.Get("engine_version").(string))
-			input.DBClusterParameterGroupName = aws.String(d.Get("neptune_cluster_parameter_group_name").(string))
+		if d.HasChange("preferred_maintenance_window") {
+			input.PreferredMaintenanceWindow = aws.String(d.Get("preferred_maintenance_window").(string))
 		}
 
 		if d.HasChange("serverless_v2_scaling_configuration") {
 			input.ServerlessV2ScalingConfiguration = expandServerlessConfiguration(d.Get("serverless_v2_scaling_configuration").([]interface{}))
 		}
 
+		if d.HasChange("storage_type") {
+			input.StorageType = aws.String(d.Get("storage_type").(string))
+		}
+
+		if d.HasChange("vpc_security_group_ids") {
+			if v := d.Get("vpc_security_group_ids").(*schema.Set); v.Len() > 0 {
+				input.VpcSecurityGroupIds = flex.ExpandStringSet(v)
+			} else {
+				input.VpcSecurityGroupIds = aws.StringSlice([]string{})
+			}
+		}
+
 		_, err := tfresource.RetryWhen(ctx, 5*time.Minute,
 			func() (interface{}, error) {
 				return conn.ModifyDBClusterWithContext(ctx, input)
diff --git a/internal/service/neptune/cluster_endpoint_test.go b/internal/service/neptune/cluster_endpoint_test.go
index 51706a82174d..e32f752f0aa1 100644
--- a/internal/service/neptune/cluster_endpoint_test.go
+++ b/internal/service/neptune/cluster_endpoint_test.go
@@ -205,7 +205,7 @@ resource "aws_neptune_cluster" "test" {
   cluster_identifier                   = %[1]q
   availability_zones                   = local.availability_zone_names
   engine                               = "neptune"
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
   skip_final_snapshot                  = true
 }
 `, rName))
diff --git a/internal/service/neptune/cluster_instance.go b/internal/service/neptune/cluster_instance.go
index a92a40340979..352a129c8855 100644
--- a/internal/service/neptune/cluster_instance.go
+++ b/internal/service/neptune/cluster_instance.go
@@ -170,6 +170,10 @@ func ResourceClusterInstance() *schema.Resource {
 				Type:     schema.TypeBool,
 				Computed: true,
 			},
+			"storage_type": {
+				Type:     schema.TypeString,
+				Computed: true,
+			},
 			names.AttrTags:    tftags.TagsSchema(),
 			names.AttrTagsAll: tftags.TagsSchemaComputed(),
 			"writer": {
@@ -282,6 +286,7 @@ func resourceClusterInstanceRead(ctx context.Context, d *schema.ResourceData, me
 	d.Set("promotion_tier", db.PromotionTier)
 	d.Set("publicly_accessible", db.PubliclyAccessible)
 	d.Set("storage_encrypted", db.StorageEncrypted)
+	d.Set("storage_type", db.StorageType)
 
 	if db.Endpoint != nil {
 		address := aws.StringValue(db.Endpoint.Address)
diff --git a/internal/service/neptune/cluster_instance_test.go b/internal/service/neptune/cluster_instance_test.go
index b81e71cfa29c..5a713fa16114 100644
--- a/internal/service/neptune/cluster_instance_test.go
+++ b/internal/service/neptune/cluster_instance_test.go
@@ -59,6 +59,7 @@ func TestAccNeptuneClusterInstance_basic(t *testing.T) {
 					resource.TestCheckResourceAttr(resourceName, "promotion_tier", "3"),
 					resource.TestCheckResourceAttr(resourceName, "publicly_accessible", "false"),
 					resource.TestCheckResourceAttr(resourceName, "storage_encrypted", "false"),
+					resource.TestCheckResourceAttr(resourceName, "storage_type", "standard"),
 					resource.TestCheckResourceAttr(resourceName, "tags.%", "0"),
 					resource.TestCheckResourceAttr(resourceName, "writer", "true"),
 				),
@@ -352,7 +353,7 @@ data "aws_neptune_orderable_db_instance" "test" {
 
 resource "aws_neptune_parameter_group" "test" {
   name   = %[1]q
-  family = "neptune1.2"
+  family = "neptune1.3"
 
   parameter {
     name  = "neptune_query_timeout"
@@ -368,7 +369,7 @@ resource "aws_neptune_cluster" "test" {
   cluster_identifier                   = %[1]q
   availability_zones                   = slice(data.aws_availability_zones.available.names, 0, min(3, length(data.aws_availability_zones.available.names)))
   engine                               = "neptune"
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
   skip_final_snapshot                  = true
 }
 `, rName))
@@ -494,7 +495,7 @@ resource "aws_neptune_subnet_group" "test" {
 resource "aws_neptune_cluster" "test" {
   cluster_identifier                   = %[1]q
   neptune_subnet_group_name            = aws_neptune_subnet_group.test.name
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
   skip_final_snapshot                  = true
 }
 `, rName))
@@ -539,7 +540,7 @@ resource "aws_neptune_cluster" "test" {
   storage_encrypted   = true
   kms_key_arn         = aws_kms_key.test.arn
 
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
 }
 `, rName))
 }
diff --git a/internal/service/neptune/cluster_snapshot_test.go b/internal/service/neptune/cluster_snapshot_test.go
index 1fe689dc2d7b..51454e18b7a3 100644
--- a/internal/service/neptune/cluster_snapshot_test.go
+++ b/internal/service/neptune/cluster_snapshot_test.go
@@ -140,7 +140,7 @@ resource "aws_neptune_cluster" "test" {
   cluster_identifier  = %[1]q
   skip_final_snapshot = true
 
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
 }
 
 resource "aws_neptune_cluster_snapshot" "test" {
diff --git a/internal/service/neptune/cluster_test.go b/internal/service/neptune/cluster_test.go
index 385b48a66807..0e7efd997d55 100644
--- a/internal/service/neptune/cluster_test.go
+++ b/internal/service/neptune/cluster_test.go
@@ -74,7 +74,7 @@ func TestAccNeptuneCluster_basic(t *testing.T) {
 					resource.TestCheckResourceAttr(resourceName, "iam_database_authentication_enabled", "false"),
 					resource.TestCheckResourceAttr(resourceName, "iam_roles.#", "0"),
 					resource.TestCheckResourceAttr(resourceName, "kms_key_arn", ""),
-					resource.TestCheckResourceAttr(resourceName, "neptune_cluster_parameter_group_name", "default.neptune1.2"),
+					resource.TestCheckResourceAttr(resourceName, "neptune_cluster_parameter_group_name", "default.neptune1.3"),
 					resource.TestCheckNoResourceAttr(resourceName, "neptune_instance_parameter_group_name"),
 					resource.TestCheckResourceAttr(resourceName, "neptune_subnet_group_name", "default"),
 					resource.TestCheckResourceAttr(resourceName, "port", "8182"),
@@ -86,6 +86,7 @@ func TestAccNeptuneCluster_basic(t *testing.T) {
 					resource.TestCheckResourceAttr(resourceName, "skip_final_snapshot", "true"),
 					resource.TestCheckNoResourceAttr(resourceName, "snapshot_identifier"),
 					resource.TestCheckResourceAttr(resourceName, "storage_encrypted", "false"),
+					resource.TestCheckResourceAttr(resourceName, "storage_type", ""),
 					resource.TestCheckResourceAttr(resourceName, "tags.%", "0"),
 					resource.TestCheckResourceAttr(resourceName, "vpc_security_group_ids.#", "1"),
 				),
@@ -648,14 +649,39 @@ func TestAccNeptuneCluster_restoreFromSnapshot(t *testing.T) {
 	})
 }
 
-func testAccCheckClusterDestroy(ctx context.Context) resource.TestCheckFunc {
-	return func(s *terraform.State) error {
-		return testAccCheckClusterDestroyWithProvider(ctx)(s, acctest.Provider)
-	}
+func TestAccNeptuneCluster_storageType(t *testing.T) {
+	ctx := acctest.Context(t)
+	var v neptune.DBCluster
+	resourceName := "aws_neptune_cluster.test"
+	rName := sdkacctest.RandomWithPrefix("tf-acc")
+
+	resource.ParallelTest(t, resource.TestCase{
+		PreCheck:                 func() { acctest.PreCheck(ctx, t) },
+		ErrorCheck:               acctest.ErrorCheck(t, neptune.EndpointsID),
+		ProtoV5ProviderFactories: acctest.ProtoV5ProviderFactories,
+		CheckDestroy:             testAccCheckClusterDestroy(ctx),
+		Steps: []resource.TestStep{
+			{
+				Config: testAccClusterConfig_storageType(rName, "standard"),
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckClusterExists(ctx, resourceName, &v),
+					resource.TestCheckResourceAttr(resourceName, "storage_type", ""),
+				),
+			},
+			testAccClusterImportStep(resourceName),
+			{
+				Config: testAccClusterConfig_storageType(rName, "iopt1"),
+				Check: resource.ComposeTestCheckFunc(
+					testAccCheckClusterExists(ctx, resourceName, &v),
+					resource.TestCheckResourceAttr(resourceName, "storage_type", "iopt1"),
+				),
+			},
+		},
+	})
 }
 
-func testAccCheckClusterDestroyWithProvider(ctx context.Context) acctest.TestCheckWithProviderFunc {
-	return func(s *terraform.State, provider *schema.Provider) error {
+func testAccCheckClusterDestroy(ctx context.Context) resource.TestCheckFunc {
+	return func(s *terraform.State) error {
 		conn := acctest.Provider.Meta().(*conns.AWSClient).NeptuneConn(ctx)
 
 		for _, rs := range s.RootModule().Resources {
@@ -764,7 +790,7 @@ resource "aws_neptune_cluster" "test" {
   cluster_identifier                   = %[1]q
   availability_zones                   = local.availability_zone_names
   engine                               = "neptune"
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
   skip_final_snapshot                  = true
 }
 `, rName))
@@ -774,7 +800,7 @@ func testAccClusterConfig_identifierGenerated() string {
 	return `
 resource "aws_neptune_cluster" "test" {
   engine                               = "neptune"
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
   skip_final_snapshot                  = true
 }
 `
@@ -785,7 +811,7 @@ func testAccClusterConfig_identifierPrefix(prefix string) string {
 resource "aws_neptune_cluster" "test" {
   cluster_identifier_prefix            = %[1]q
   engine                               = "neptune"
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
   skip_final_snapshot                  = true
 }
 `, prefix)
@@ -797,7 +823,7 @@ resource "aws_neptune_cluster" "test" {
   cluster_identifier                   = %[1]q
   availability_zones                   = local.availability_zone_names
   engine                               = "neptune"
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
   skip_final_snapshot                  = true
 
   tags = {
@@ -813,7 +839,7 @@ resource "aws_neptune_cluster" "test" {
   cluster_identifier                   = %[1]q
   availability_zones                   = local.availability_zone_names
   engine                               = "neptune"
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
   skip_final_snapshot                  = true
 
   tags = {
@@ -830,7 +856,7 @@ resource "aws_neptune_cluster" "test" {
   cluster_identifier                   = %[1]q
   availability_zones                   = local.availability_zone_names
   engine                               = "neptune"
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
   skip_final_snapshot                  = true
   copy_tags_to_snapshot                = %[2]t
 }
@@ -843,7 +869,7 @@ resource "aws_neptune_cluster" "test" {
   cluster_identifier                   = %[1]q
   availability_zones                   = local.availability_zone_names
   engine                               = "neptune"
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
   skip_final_snapshot                  = true
   deletion_protection                  = %[2]t
 }
@@ -872,7 +898,7 @@ func testAccClusterConfig_finalSnapshot(rName string) string {
 resource "aws_neptune_cluster" "test" {
   cluster_identifier                   = %[1]q
   availability_zones                   = local.availability_zone_names
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
   final_snapshot_identifier            = %[1]q
 }
 `, rName))
@@ -957,7 +983,7 @@ EOF
 resource "aws_neptune_cluster" "test" {
   cluster_identifier                   = %[1]q
   availability_zones                   = local.availability_zone_names
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
   skip_final_snapshot                  = true
 
   depends_on = [aws_iam_role.test, aws_iam_role.test-2]
@@ -1047,7 +1073,7 @@ resource "aws_neptune_cluster" "test" {
   skip_final_snapshot = true
   iam_roles           = [aws_iam_role.test.arn, aws_iam_role.test-2.arn]
 
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
 
   depends_on = [aws_iam_role.test, aws_iam_role.test-2]
 }
@@ -1099,7 +1125,7 @@ resource "aws_neptune_cluster" "test" {
   skip_final_snapshot = true
   iam_roles           = [aws_iam_role.test.arn]
 
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
 
   depends_on = [aws_iam_role.test]
 }
@@ -1134,7 +1160,7 @@ resource "aws_kms_key" "test" {
 resource "aws_neptune_cluster" "test" {
   cluster_identifier                   = %[1]q
   availability_zones                   = local.availability_zone_names
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
   storage_encrypted                    = true
   kms_key_arn                          = aws_kms_key.test.arn
   skip_final_snapshot                  = true
@@ -1150,7 +1176,7 @@ resource "aws_neptune_cluster" "test" {
   storage_encrypted   = true
   skip_final_snapshot = true
 
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
 }
 `, rName))
 }
@@ -1165,7 +1191,7 @@ resource "aws_neptune_cluster" "test" {
   preferred_maintenance_window = "tue:04:00-tue:04:30"
   skip_final_snapshot          = true
 
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
 }
 `, rName))
 }
@@ -1181,7 +1207,7 @@ resource "aws_neptune_cluster" "test" {
   apply_immediately            = true
   skip_final_snapshot          = true
 
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
 }
 `, rName))
 }
@@ -1194,7 +1220,7 @@ resource "aws_neptune_cluster" "test" {
   iam_database_authentication_enabled = true
   skip_final_snapshot                 = true
 
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
 }
 `, rName))
 }
@@ -1207,7 +1233,7 @@ resource "aws_neptune_cluster" "test" {
   skip_final_snapshot            = true
   enable_cloudwatch_logs_exports = ["audit", "slowquery"]
 
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
 }
 `, rName))
 }
@@ -1416,7 +1442,7 @@ resource "aws_security_group" "test" {
 
 resource "aws_neptune_cluster" "source" {
   cluster_identifier                   = "%[1]s-src"
-  neptune_cluster_parameter_group_name = "default.neptune1.2"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
   skip_final_snapshot                  = true
   storage_encrypted                    = true
   kms_key_arn                          = aws_kms_key.test1.arn
@@ -1453,3 +1479,18 @@ resource "aws_neptune_cluster" "test" {
 }
 `, rName)
 }
+
+func testAccClusterConfig_storageType(rName, storageType string) string {
+	return acctest.ConfigCompose(testAccClusterConfig_base(), fmt.Sprintf(`
+resource "aws_neptune_cluster" "test" {
+  cluster_identifier                   = %[1]q
+  availability_zones                   = local.availability_zone_names
+  engine                               = "neptune"
+  engine_version                       = "1.3.0.0"
+  neptune_cluster_parameter_group_name = "default.neptune1.3"
+  skip_final_snapshot                  = true
+  storage_type                         = %[2]q
+  apply_immediately                    = true
+}
+`, rName, storageType))
+}
diff --git a/internal/service/neptune/consts.go b/internal/service/neptune/consts.go
index f2f5f6c41467..3b6917a0f33d 100644
--- a/internal/service/neptune/consts.go
+++ b/internal/service/neptune/consts.go
@@ -21,6 +21,18 @@ func engine_Values() []string {
 	}
 }
 
+const (
+	storageTypeStandard = "standard"
+	storageTypeIopt1    = "iopt1"
+)
+
+func storageType_Values() []string {
+	return []string{
+		storageTypeStandard,
+		storageTypeIopt1,
+	}
+}
+
 const (
 	clusterEndpointStatusAvailable = "available"
 	clusterEndpointStatusCreating  = "creating"
diff --git a/website/docs/cdktf/python/r/neptune_cluster.html.markdown b/website/docs/cdktf/python/r/neptune_cluster.html.markdown
index c055f439f054..83c8e9041b07 100644
--- a/website/docs/cdktf/python/r/neptune_cluster.html.markdown
+++ b/website/docs/cdktf/python/r/neptune_cluster.html.markdown
@@ -70,6 +70,7 @@ This resource supports the following arguments:
 * `neptune_subnet_group_name` - (Optional) A Neptune subnet group to associate with this Neptune instance.
 * `neptune_cluster_parameter_group_name` - (Optional) A cluster parameter group to associate with the cluster.
 * `neptune_instance_parameter_group_name` - (Optional) The name of the DB parameter group to apply to all instances of the DB cluster.
+* `storage_type` - (Optional) Storage type associated with the cluster `standard/iopt1`. Default: `standard`
 * `preferred_backup_window` - (Optional) The daily time range during which automated backups are created if automated backups are enabled using the BackupRetentionPeriod parameter. Time in UTC. Default: A 30-minute window selected at random from an 8-hour block of time per regionE.g., 04:00-09:00
 * `preferred_maintenance_window` - (Optional) The weekly time range during which system maintenance can occur, in (UTC) e.g., wed:04:00-wed:04:30
 * `port` - (Optional) The port on which the Neptune accepts connections. Default is `8182`.
diff --git a/website/docs/cdktf/python/r/neptune_cluster_instance.html.markdown b/website/docs/cdktf/python/r/neptune_cluster_instance.html.markdown
index d1837ab9e932..9fafbbe22dd0 100644
--- a/website/docs/cdktf/python/r/neptune_cluster_instance.html.markdown
+++ b/website/docs/cdktf/python/r/neptune_cluster_instance.html.markdown
@@ -70,6 +70,7 @@ This resource supports the following arguments:
 * `identifier_prefix` - (Optional, Forces new resource) Creates a unique identifier beginning with the specified prefix. Conflicts with `identifier`.
 * `instance_class` - (Required) The instance class to use.
 * `neptune_subnet_group_name` - (Required if `publicly_accessible = false`, Optional otherwise) A subnet group to associate with this neptune instance. **NOTE:** This must match the `neptune_subnet_group_name` of the attached [`aws_neptune_cluster`](/docs/providers/aws/r/neptune_cluster.html).
+* `storage_type` - (Optional) Storage type associated with the cluster `standard/iopt1`. Default: `standard`
 * `neptune_parameter_group_name` - (Optional) The name of the neptune parameter group to associate with this instance.
 * `port` - (Optional) The port on which the DB accepts connections. Defaults to `8182`.
 * `preferred_backup_window` - (Optional) The daily time range during which automated backups are created if automated backups are enabled. Eg: "04:00-09:00"
diff --git a/website/docs/cdktf/typescript/r/neptune_cluster_instance.html.markdown b/website/docs/cdktf/typescript/r/neptune_cluster_instance.html.markdown
index 901decadb882..ecd19a513aff 100644
--- a/website/docs/cdktf/typescript/r/neptune_cluster_instance.html.markdown
+++ b/website/docs/cdktf/typescript/r/neptune_cluster_instance.html.markdown
@@ -74,6 +74,7 @@ This resource supports the following arguments:
 * `instanceClass` - (Required) The instance class to use.
 * `neptuneSubnetGroupName` - (Required if `publicly_accessible = false`, Optional otherwise) A subnet group to associate with this neptune instance. **NOTE:** This must match the `neptune_subnet_group_name` of the attached [`aws_neptune_cluster`](/docs/providers/aws/r/neptune_cluster.html).
 * `neptuneParameterGroupName` - (Optional) The name of the neptune parameter group to associate with this instance.
+* `storage_type` - (Optional) Storage type associated with the cluster `standard/iopt1`. Default: `standard`
 * `port` - (Optional) The port on which the DB accepts connections. Defaults to `8182`.
 * `preferredBackupWindow` - (Optional) The daily time range during which automated backups are created if automated backups are enabled. Eg: "04:00-09:00"
 * `preferredMaintenanceWindow` - (Optional) The window to perform maintenance in.
diff --git a/website/docs/r/neptune_cluster.html.markdown b/website/docs/r/neptune_cluster.html.markdown
index 8466e9104342..42385459f2d4 100644
--- a/website/docs/r/neptune_cluster.html.markdown
+++ b/website/docs/r/neptune_cluster.html.markdown
@@ -57,6 +57,7 @@ This resource supports the following arguments:
 * `neptune_subnet_group_name` - (Optional) A Neptune subnet group to associate with this Neptune instance.
 * `neptune_cluster_parameter_group_name` - (Optional) A cluster parameter group to associate with the cluster.
 * `neptune_instance_parameter_group_name` - (Optional) The name of the DB parameter group to apply to all instances of the DB cluster.
+* `storage_type` - (Optional) Storage type associated with the cluster `standard/iopt1`. Default: `standard`
 * `preferred_backup_window` - (Optional) The daily time range during which automated backups are created if automated backups are enabled using the BackupRetentionPeriod parameter. Time in UTC. Default: A 30-minute window selected at random from an 8-hour block of time per regionE.g., 04:00-09:00
 * `preferred_maintenance_window` - (Optional) The weekly time range during which system maintenance can occur, in (UTC) e.g., wed:04:00-wed:04:30
 * `port` - (Optional) The port on which the Neptune accepts connections. Default is `8182`.
diff --git a/website/docs/r/neptune_cluster_instance.html.markdown b/website/docs/r/neptune_cluster_instance.html.markdown
index 257f5a160364..48c61727d98f 100644
--- a/website/docs/r/neptune_cluster_instance.html.markdown
+++ b/website/docs/r/neptune_cluster_instance.html.markdown
@@ -72,6 +72,7 @@ This resource exports the following attributes in addition to the arguments abov
 * `id` - The Instance identifier
 * `kms_key_arn` - The ARN for the KMS encryption key if one is set to the neptune cluster.
 * `storage_encrypted` - Specifies whether the neptune cluster is encrypted.
+* `storage_type` - Storage type associated with the cluster `standard/iopt1`.
 * `tags_all` - A map of tags assigned to the resource, including those inherited from the provider [`default_tags` configuration block](https://registry.terraform.io/providers/hashicorp/aws/latest/docs#default_tags-configuration-block).
 * `writer` – Boolean indicating if this instance is writable. `False` indicates this instance is a read replica.