diff --git a/openapi/openapiv2.json b/openapi/openapiv2.json
index 1391f113a..70e94bb26 100644
--- a/openapi/openapiv2.json
+++ b/openapi/openapiv2.json
@@ -17251,6 +17251,10 @@
         },
         "state": {
           "$ref": "#/definitions/v1ReplicationState"
+        },
+        "replicationRampDuration": {
+          "type": "string",
+          "description": "Ramp duration for passive clusters added by an UpdateNamespace request; unset or non-positive disables gradual connect.\nThis field is not persisted and is omitted from namespace responses."
         }
       }
     },
diff --git a/openapi/openapiv3.yaml b/openapi/openapiv3.yaml
index ab3e297e5..767827a61 100644
--- a/openapi/openapiv3.yaml
+++ b/openapi/openapiv3.yaml
@@ -13564,6 +13564,12 @@ components:
             - REPLICATION_STATE_HANDOVER
           type: string
           format: enum
+        replicationRampDuration:
+          pattern: ^-?(?:0|[1-9][0-9]{0,11})(?:\.[0-9]{1,9})?s$
+          type: string
+          description: |-
+            Ramp duration for passive clusters added by an UpdateNamespace request; unset or non-positive disables gradual connect.
+             This field is not persisted and is omitted from namespace responses.
     NewWorkflowExecutionInfo:
       type: object
       properties:
diff --git a/temporal/api/replication/v1/message.proto b/temporal/api/replication/v1/message.proto
index 0c2f614eb..f69f29ea3 100644
--- a/temporal/api/replication/v1/message.proto
+++ b/temporal/api/replication/v1/message.proto
@@ -9,6 +9,7 @@ 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";
@@ -21,6 +22,9 @@ message NamespaceReplicationConfig {
     string active_cluster_name = 1;
     repeated ClusterReplicationConfig clusters = 2;
     temporal.api.enums.v1.ReplicationState state = 3;
+    // Ramp duration for passive clusters added by an UpdateNamespace request; unset or non-positive disables gradual connect.
+    // This field is not persisted and is omitted from namespace responses.
+    google.protobuf.Duration replication_ramp_duration = 4;
 }
 
 // Represents a historical replication status of a Namespace