PUT my-index
{
  "mappings": {
    "properties": {
      "embedding": { "type": "dense_vector", "dims": 768, "index": true, "similarity": "cosine" }
    }
  }
}

POST my-index/_search
{
  "knn": {
    "field": "embedding",
    "query_vector": [...],
    "k": 5,
    "num_candidates": 10
  }
}