diff --git a/openapi/openapiv2.json b/openapi/openapiv2.json
index 9a475d2d2..bb5acc172 100644
--- a/openapi/openapiv2.json
+++ b/openapi/openapiv2.json
@@ -14952,6 +14952,10 @@
       "properties": {
         "clusterName": {
           "type": "string"
+        },
+        "replicationRampDuration": {
+          "type": "string",
+          "description": "Ramp duration when this cluster is added as passive by UpdateNamespace; unset or non-positive disables gradual connect.\nThis field is not persisted and is omitted from namespace responses."
         }
       }
     },
diff --git a/openapi/openapiv3.yaml b/openapi/openapiv3.yaml
index 1cba692a1..1d4c2cdc0 100644
--- a/openapi/openapiv3.yaml
+++ b/openapi/openapiv3.yaml
@@ -11089,6 +11089,12 @@ components:
       properties:
         clusterName:
           type: string
+        replicationRampDuration:
+          pattern: ^-?(?:0|[1-9][0-9]{0,11})(?:\.[0-9]{1,9})?s$
+          type: string
+          description: |-
+            Ramp duration when this cluster is added as passive by UpdateNamespace; unset or non-positive disables gradual connect.
+             This field is not persisted and is omitted from namespace responses.
     CompatibleBuildIdRedirectRule:
       type: object
       properties:
diff --git a/temporal/api/replication/v1/message.proto b/temporal/api/replication/v1/message.proto
index 0c2f614eb..241e93066 100644
--- a/temporal/api/replication/v1/message.proto
+++ b/temporal/api/replication/v1/message.proto
@@ -9,12 +9,16 @@ option java_outer_classname = "MessageProto";
 option ruby_package = "Temporalio::Api::Replication::V1";
 option csharp_namespace = "Temporalio.Api.Replication.V1";
 
+import "google/protobuf/duration.proto";
 import "google/protobuf/timestamp.proto";
 
 import "temporal/api/enums/v1/namespace.proto";
 
 message ClusterReplicationConfig {
     string cluster_name = 1;
+    // Ramp duration when this cluster is added as passive by UpdateNamespace; unset or non-positive disables gradual connect.
+    // This field is not persisted and is omitted from namespace responses.
+    google.protobuf.Duration replication_ramp_duration = 2;
 }
 
 message NamespaceReplicationConfig {