Ultrawarm Storage for kNN index

OpenSearch
1

Hi,

I am trying to migrate our kNN index to Ultrawarm storage. Currently all our data is in hot storage which is costly. When I am trying to migrate our test index from OpenSearch dashboard it is giving error as

{
  "error" : {
    "root_cause" : [
      {
        "type" : "illegal_argument_exception",
        "reason" : "Rejecting migration request because index [testindex] is a KNN index and cannot be migrated to [WARM]"
      }
    ],
    "type" : "illegal_argument_exception",
    "reason" : "Rejecting migration request because index [testindex] is a KNN index and cannot be migrated to [WARM]"
  },
  "status" : 400
}

I dont see any documentation around it. Can we not migrate kNN index to any other storage other that Hot storage ?