fix: normalize vector store scores to similarity (higher = better)

The threshold parameter in Memory.search() was silently broken for 11
vector stores because they returned raw distance scores (lower = better)
while the threshold check assumed similarity scores (higher = better).
This caused threshold filtering to be inverted — good matches got
dropped and bad matches passed through.

Convert all affected vector stores to return similarity scores:
- Cosine distance stores: score = max(0.0, 1.0 - distance)
- L2 distance stores: score = 1.0 / (1.0 + distance)
- Stores computing similarity then discarding it: return similarity directly

Fixes #4453
Related: #3283

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

mem0/vector_stores/azure_mysql.py

@@ -286,13 +286,12 @@ class AzureMySQL(VectorStoreBase):
 
         for row in results:
             vec = np.array(json.loads(row['vector']))
-            # Cosine similarity
+            # Cosine similarity (higher = more similar)
-            similarity = np.dot(query_vec, vec) / (np.linalg.norm(query_vec) * np.linalg.norm(vec))
+            similarity = float(np.dot(query_vec, vec) / (np.linalg.norm(query_vec) * np.linalg.norm(vec)))
-            distance = 1 - similarity
+            scored_results.append((row['id'], similarity, row['payload']))
-            scored_results.append((row['id'], distance, row['payload']))
 
-        # Sort by distance and limit
+        # Sort by similarity (descending) and limit
-        scored_results.sort(key=lambda x: x[1])
+        scored_results.sort(key=lambda x: x[1], reverse=True)
         scored_results = scored_results[:limit]
 
         return [

mem0/vector_stores/base.py

@@ -14,7 +14,15 @@ class VectorStoreBase(ABC):
 
     @abstractmethod
     def search(self, query, vectors, limit=5, filters=None):
-        """Search for similar vectors."""
+        """Search for similar vectors.
+
+        All implementations must return similarity scores where higher values
+        indicate greater similarity (range [0, 1] preferred). Implementations
+        using distance metrics must convert to similarity before returning:
+        - Cosine distance: score = max(0.0, 1.0 - distance)
+        - L2 distance: score = 1.0 / (1.0 + distance)
+        - Inner product: score = value (already higher = better)
+        """
         pass
 
     @abstractmethod

mem0/vector_stores/cassandra.py

@@ -247,9 +247,8 @@ class CassandraDB(VectorStoreBase):
 
                 vec = np.array(row.vector)
                 
-                # Cosine similarity
+                # Cosine similarity (higher = more similar)
-                similarity = np.dot(query_vec, vec) / (np.linalg.norm(query_vec) * np.linalg.norm(vec))
+                similarity = float(np.dot(query_vec, vec) / (np.linalg.norm(query_vec) * np.linalg.norm(vec)))
-                distance = 1 - similarity
 
                 # Apply filters if provided
                 if filters:
@@ -261,10 +260,10 @@ class CassandraDB(VectorStoreBase):
                     except json.JSONDecodeError:
                         continue
 
-                scored_results.append((row.id, distance, row.payload))
+                scored_results.append((row.id, similarity, row.payload))
 
-            # Sort by distance and limit
+            # Sort by similarity (descending) and limit
-            scored_results.sort(key=lambda x: x[1])
+            scored_results.sort(key=lambda x: x[1], reverse=True)
             scored_results = scored_results[:limit]
 
             return [

mem0/vector_stores/chroma.py

@@ -97,9 +97,12 @@ class ChromaDB(VectorStoreBase):
 
         result = []
         for i in range(max_length):
+            # Convert L2 distance to similarity score (higher = more similar)
+            raw_distance = distances[i] if isinstance(distances, list) and distances and i < len(distances) else None
+            score = 1.0 / (1.0 + raw_distance) if raw_distance is not None else None
             entry = OutputData(
                 id=ids[i] if isinstance(ids, list) and ids and i < len(ids) else None,
-                score=(distances[i] if isinstance(distances, list) and distances and i < len(distances) else None),
+                score=score,
                 payload=(metadatas[i] if isinstance(metadatas, list) and metadatas and i < len(metadatas) else None),
             )
             result.append(entry)

mem0/vector_stores/faiss.py

@@ -146,7 +146,13 @@ class FAISS(VectorStoreBase):
 
             payload_copy = payload.copy()
 
-            score = float(scores[i])
+            raw_score = float(scores[i])
+            # Convert to similarity score (higher = more similar)
+            if self.distance_strategy.lower() == "euclidean":
+                score = 1.0 / (1.0 + raw_score)
+            else:
+                # inner_product and cosine: higher is already better
+                score = raw_score
             entry = OutputData(
                 id=vector_id,
                 score=score,

mem0/vector_stores/milvus.py

@@ -128,11 +128,17 @@ class MilvusDB(VectorStoreBase):
         memory = []
 
         for value in data:
-            uid, score, metadata = (
+            uid = value.get("id")
-                value.get("id"),
+            raw_distance = value.get("distance")
-                value.get("distance"),
+            metadata = value.get("entity", {}).get("metadata")
-                value.get("entity", {}).get("metadata"),
+
-            )
+            # Convert distance to similarity score (higher = more similar)
+            # Milvus returns: L2 = distance (lower=better), COSINE/IP = similarity (higher=better)
+            if raw_distance is not None and self.metric_type in (MetricType.L2, "L2"):
+                score = 1.0 / (1.0 + raw_distance)
+            else:
+                # COSINE and IP: Milvus already returns similarity (higher = better)
+                score = raw_distance
 
             memory_obj = OutputData(id=uid, score=score, payload=metadata)
             memory.append(memory_obj)

mem0/vector_stores/pgvector.py

@@ -241,7 +241,8 @@ class PGVector(VectorStoreBase):
             )
 
             results = cur.fetchall()
-        return [OutputData(id=str(r[0]), score=float(r[1]), payload=r[2]) for r in results]
+        # Convert cosine distance to similarity score (higher = more similar)
+        return [OutputData(id=str(r[0]), score=max(0.0, 1.0 - float(r[1])), payload=r[2]) for r in results]
 
     def delete(self, vector_id: str) -> None:
         """

mem0/vector_stores/redis.py

@@ -158,7 +158,7 @@ class RedisDB(VectorStoreBase):
         return [
             MemoryResult(
                 id=result["memory_id"],
-                score=float(result["vector_distance"]),
+                score=max(0.0, 1.0 - float(result["vector_distance"])),
                 payload={
                     "hash": result["hash"],
                     "data": result["memory"],

mem0/vector_stores/s3_vectors.py

@@ -80,7 +80,10 @@ class S3Vectors(VectorStoreBase):
                 except json.JSONDecodeError:
                     logger.warning(f"Failed to parse metadata for key {v.get('key')}")
                     payload = {}
-            results.append(OutputData(id=v.get("key"), score=v.get("distance"), payload=payload))
+            # Convert distance to similarity score (higher = more similar)
+            raw_distance = v.get("distance")
+            score = max(0.0, 1.0 - raw_distance) if raw_distance is not None else None
+            results.append(OutputData(id=v.get("key"), score=score, payload=payload))
         return results
 
     def insert(self, vectors, payloads=None, ids=None):

mem0/vector_stores/supabase.py

@@ -135,7 +135,8 @@ class Supabase(VectorStoreBase):
             data=vectors, limit=limit, filters=filters, include_metadata=True, include_value=True
         )
 
-        return [OutputData(id=str(result[0]), score=float(result[1]), payload=result[2]) for result in results]
+        # Convert cosine distance to similarity score (higher = more similar)
+        return [OutputData(id=str(result[0]), score=max(0.0, 1.0 - float(result[1])), payload=result[2]) for result in results]
 
     def delete(self, vector_id: str):
         """

mem0/vector_stores/valkey.py

@@ -379,7 +379,9 @@ class ValkeyDB(VectorStoreBase):
         memory_results = []
         for doc in results.docs:
             # Extract the score
-            score = float(doc.vector_score) if hasattr(doc, "vector_score") else None
+            # Convert cosine distance to similarity score (higher = more similar)
+            raw_distance = float(doc.vector_score) if hasattr(doc, "vector_score") else None
+            score = max(0.0, 1.0 - raw_distance) if raw_distance is not None else None
 
             # Create the payload
             payload = {

mem0/vector_stores/vertex_ai_vector_search.py

@@ -115,7 +115,7 @@ class GoogleMatchingEngine(VectorStoreBase):
             output_data.append(
                 OutputData(
                     id=result.get("datapoint").get("datapointId"),
-                    score=result.get("distance"),
+                    score=max(0.0, 1.0 - result.get("distance")) if result.get("distance") is not None else None,
                     payload=result.get("datapoint").get("metadata"),
                 )
             )
@@ -262,7 +262,9 @@ class GoogleMatchingEngine(VectorStoreBase):
                             logger.debug("Adding %s: %s", restrict.name, restrict.allow_tokens[0])
                             payload[restrict.name] = restrict.allow_tokens[0]
 
-                output_data = OutputData(id=neighbor.id, score=neighbor.distance, payload=payload)
+                # Convert distance to similarity score (higher = more similar)
+                score = max(0.0, 1.0 - neighbor.distance) if neighbor.distance is not None else None
+                output_data = OutputData(id=neighbor.id, score=score, payload=payload)
                 results.append(output_data)
 
             logger.debug("Returning %d results", len(results))
@@ -406,7 +408,8 @@ class GoogleMatchingEngine(VectorStoreBase):
                                 if restrict.allow_list:
                                     payload[restrict.namespace] = restrict.allow_list[0]
 
-                        return OutputData(id=neighbor.datapoint.datapoint_id, score=neighbor.distance, payload=payload)
+                        score = max(0.0, 1.0 - neighbor.distance) if neighbor.distance is not None else None
+                        return OutputData(id=neighbor.datapoint.datapoint_id, score=score, payload=payload)
 
                 logger.debug("No results found")
                 return None

tests/vector_stores/test_chroma.py

@@ -45,7 +45,7 @@ def test_search_vectors(chromadb_instance, mock_chromadb_client):
 
     assert len(results) == 2
     assert results[0].id == "id1"
-    assert results[0].score == 0.1
+    assert abs(results[0].score - (1.0 / (1.0 + 0.1))) < 1e-9  # L2 distance 0.1 -> similarity
     assert results[0].payload == {"name": "vector1"}
 
 
@@ -150,7 +150,7 @@ def test_get_vector(chromadb_instance):
     chromadb_instance.collection.get.assert_called_once_with(ids=["id1"])
 
     assert result.id == "id1"
-    assert result.score == 0.1
+    assert abs(result.score - (1.0 / (1.0 + 0.1))) < 1e-9  # L2 distance 0.1 -> similarity
     assert result.payload == {"name": "vector1"}
 
 

tests/vector_stores/test_milvus.py

@@ -129,7 +129,7 @@ class TestMilvusDB:
         # Verify results are parsed correctly
         assert len(results) == 1
         assert results[0].id == "mem1"
-        assert results[0].score == 0.8
+        assert results[0].score == 0.8  # COSINE: Milvus returns similarity directly
 
     def test_search_different_user_ids(self, milvus_db, mock_milvus_client):
         """Test that search works with different user_ids (reproduces reported bug)."""
@@ -228,10 +228,10 @@ class TestMilvusDB:
         
         assert len(parsed) == 2
         assert parsed[0].id == "mem1"
-        assert parsed[0].score == 0.9
+        assert parsed[0].score == 0.9  # COSINE: Milvus returns similarity directly
         assert parsed[0].payload == {"user_id": "alice"}
         assert parsed[1].id == "mem2"
-        assert parsed[1].score == 0.85
+        assert parsed[1].score == 0.85  # COSINE: Milvus returns similarity directly
 
     def test_update_with_none_vector_fetches_existing(self, milvus_db, mock_milvus_client):
         """Test that update with vector=None fetches the existing vector (fixes #3708)."""

tests/vector_stores/test_pgvector.py

@@ -445,9 +445,9 @@ class TestPGVector(unittest.TestCase):
         # Verify results
         self.assertEqual(len(results), 2)
         self.assertEqual(results[0].id, self.test_ids[0])
-        self.assertEqual(results[0].score, 0.1)
+        self.assertEqual(results[0].score, 0.9)
         self.assertEqual(results[1].id, self.test_ids[1])
-        self.assertEqual(results[1].score, 0.2)
+        self.assertEqual(results[1].score, 0.8)
 
     @patch('mem0.vector_stores.pgvector.PSYCOPG_VERSION', 2)
     @patch('mem0.vector_stores.pgvector.ConnectionPool')
@@ -494,9 +494,9 @@ class TestPGVector(unittest.TestCase):
         # Verify results
         self.assertEqual(len(results), 2)
         self.assertEqual(results[0].id, self.test_ids[0])
-        self.assertEqual(results[0].score, 0.1)
+        self.assertEqual(results[0].score, 0.9)
         self.assertEqual(results[1].id, self.test_ids[1])
-        self.assertEqual(results[1].score, 0.2)
+        self.assertEqual(results[1].score, 0.8)
 
     @patch('mem0.vector_stores.pgvector.PSYCOPG_VERSION', 3)
     @patch('mem0.vector_stores.pgvector.ConnectionPool')
@@ -1140,7 +1140,7 @@ class TestPGVector(unittest.TestCase):
         # Verify results
         self.assertEqual(len(results), 1)
         self.assertEqual(results[0].id, self.test_ids[0])
-        self.assertEqual(results[0].score, 0.1)
+        self.assertEqual(results[0].score, 0.9)
         self.assertEqual(results[0].payload["user_id"], "alice")
         self.assertEqual(results[0].payload["agent_id"], "agent1")
         self.assertEqual(results[0].payload["run_id"], "run1")
@@ -1190,7 +1190,7 @@ class TestPGVector(unittest.TestCase):
         # Verify results
         self.assertEqual(len(results), 1)
         self.assertEqual(results[0].id, self.test_ids[0])
-        self.assertEqual(results[0].score, 0.1)
+        self.assertEqual(results[0].score, 0.9)
         self.assertEqual(results[0].payload["user_id"], "alice")
         self.assertEqual(results[0].payload["agent_id"], "agent1")
         self.assertEqual(results[0].payload["run_id"], "run1")
@@ -1240,7 +1240,7 @@ class TestPGVector(unittest.TestCase):
         # Verify results
         self.assertEqual(len(results), 1)
         self.assertEqual(results[0].id, self.test_ids[0])
-        self.assertEqual(results[0].score, 0.1)
+        self.assertEqual(results[0].score, 0.9)
         self.assertEqual(results[0].payload["user_id"], "alice")
 
     @patch('mem0.vector_stores.pgvector.PSYCOPG_VERSION', 2)
@@ -1288,7 +1288,7 @@ class TestPGVector(unittest.TestCase):
         # Verify results
         self.assertEqual(len(results), 1)
         self.assertEqual(results[0].id, self.test_ids[0])
-        self.assertEqual(results[0].score, 0.1)
+        self.assertEqual(results[0].score, 0.9)
         self.assertEqual(results[0].payload["user_id"], "alice")
 
     @patch('mem0.vector_stores.pgvector.PSYCOPG_VERSION', 3)
@@ -1336,9 +1336,9 @@ class TestPGVector(unittest.TestCase):
         # Verify results
         self.assertEqual(len(results), 2)
         self.assertEqual(results[0].id, self.test_ids[0])
-        self.assertEqual(results[0].score, 0.1)
+        self.assertEqual(results[0].score, 0.9)
         self.assertEqual(results[1].id, self.test_ids[1])
-        self.assertEqual(results[1].score, 0.2)
+        self.assertEqual(results[1].score, 0.8)
 
     @patch('mem0.vector_stores.pgvector.PSYCOPG_VERSION', 2)
     @patch('mem0.vector_stores.pgvector.ConnectionPool')
@@ -1385,9 +1385,9 @@ class TestPGVector(unittest.TestCase):
         # Verify results
         self.assertEqual(len(results), 2)
         self.assertEqual(results[0].id, self.test_ids[0])
-        self.assertEqual(results[0].score, 0.1)
+        self.assertEqual(results[0].score, 0.9)
         self.assertEqual(results[1].id, self.test_ids[1])
-        self.assertEqual(results[1].score, 0.2)
+        self.assertEqual(results[1].score, 0.8)
 
     @patch('mem0.vector_stores.pgvector.PSYCOPG_VERSION', 3)
     @patch('mem0.vector_stores.pgvector.ConnectionPool')

tests/vector_stores/test_s3_vectors.py

@@ -157,7 +157,7 @@ def test_search(mock_boto_client):
     mock_boto_client.query_vectors.assert_called_once()
     assert len(results) == 1
     assert results[0].id == "id1"
-    assert results[0].score == 0.9
+    assert abs(results[0].score - 0.1) < 1e-9  # distance 0.9 -> similarity 0.1
 
 
 def test_get(mock_boto_client):

tests/vector_stores/test_supabase.py

@@ -75,7 +75,7 @@ def test_search_vectors(supabase_instance, mock_collection):
 
     assert len(results) == 2
     assert results[0].id == "id1"
-    assert results[0].score == 0.9
+    assert abs(results[0].score - 0.1) < 1e-9  # cosine distance 0.9 -> similarity 0.1
     assert results[0].payload == {"name": "vector1"}
 
 

tests/vector_stores/test_vertex_ai_vector_search.py

@@ -112,7 +112,7 @@ def test_search_vectors(vector_store, mock_vertex_ai):
 
     assert len(results) == 1
     assert results[0].id == "test-id"
-    assert results[0].score == 0.1
+    assert results[0].score == 0.9  # distance 0.1 -> similarity 0.9
     assert results[0].payload == {"user_id": "test_user"}