diff --git a/rag/utils/opensearch_conn.py b/rag/utils/opensearch_conn.py
index 2239102ef3..e9909d978c 100644
--- a/rag/utils/opensearch_conn.py
+++ b/rag/utils/opensearch_conn.py
@@ -666,6 +666,23 @@ class OSConnection(DocStoreConnection):
     def get_doc_ids(self, res):
         return [d["_id"] for d in res["hits"]["hits"]]
 
+    def get_scores(self, res) -> dict[str, float]:
+        """
+        Map hit `_id` to its raw `_score`. Used by rag/nlp/search.py:_knn_scores()
+        to recover the cosine similarity returned by a KNN-only second-pass search
+        without pulling the chunk vectors out of the index. OpenSearch hit headers
+        carry `_score` exactly like Elasticsearch, so this mirrors
+        ESConnectionBase.get_scores.
+        """
+        out = {}
+        for d in res.get("hits", {}).get("hits", []):
+            doc_id = d.get("_id")
+            if doc_id is None:
+                continue
+            score = d.get("_score")
+            out[doc_id] = float(score) if score is not None else 0.0
+        return out
+
     def __getSource(self, res):
         rr = []
         for d in res["hits"]["hits"]: