SERVER-79498 Introduce vectorSearch aggregation stager6.0.10-rc0r6.0.10

Co-authored-by: Chi-I Huang <chii.huang@mongodb.com>
Co-authored-by: Hima Sheth <hima.sheth@mongodb.com>

11 files changed, 107 insertions, 12 deletions

diff --git a/src/mongo/db/exec/document_value/document.cpp b/src/mongo/db/exec/document_value/document.cpp
index fd50895c9a1..4488af81f3b 100644
--- a/src/mongo/db/exec/document_value/document.cpp
+++ b/src/mongo/db/exec/document_value/document.cpp
@@ -90,7 +90,8 @@ const StringDataSet Document::allMetadataFieldNames{Document::metaFieldTextScore
                                                     Document::metaFieldSearchHighlights,
                                                     Document::metaFieldSearchSortValues,
                                                     Document::metaFieldIndexKey,
-                                                    Document::metaFieldSearchScoreDetails};
+                                                    Document::metaFieldSearchScoreDetails,
+                                                    Document::metaFieldVectorSearchScore};
 
 DocumentStorageIterator::DocumentStorageIterator(DocumentStorage* storage, BSONObjIterator bsonIt)
     : _bsonIt(std::move(bsonIt)),
@@ -467,6 +468,8 @@ void DocumentStorage::loadLazyMetadata() const {
                 _metadataFields.setSearchScoreDetails(elem.Obj());
             } else if (fieldName == Document::metaFieldSearchSortValues) {
                 _metadataFields.setSearchSortValues(elem.Obj());
+            } else if (fieldName == Document::metaFieldVectorSearchScore) {
+                _metadataFields.setVectorSearchScore(elem.Double());
             }
         }
     }
@@ -537,6 +540,7 @@ constexpr StringData Document::metaFieldSearchScore;
 constexpr StringData Document::metaFieldSearchHighlights;
 constexpr StringData Document::metaFieldSearchScoreDetails;
 constexpr StringData Document::metaFieldSearchSortValues;
+constexpr StringData Document::metaFieldVectorSearchScore;
 
 void Document::toBsonWithMetaData(BSONObjBuilder* builder) const {
     toBson(builder);
@@ -567,6 +571,9 @@ void Document::toBsonWithMetaData(BSONObjBuilder* builder) const {
     if (metadata().hasSearchSortValues()) {
         builder->append(metaFieldSearchSortValues, metadata().getSearchSortValues());
     }
+    if (metadata().hasVectorSearchScore()) {
+        builder->append(metaFieldVectorSearchScore, metadata().getVectorSearchScore());
+    }
 }
 
 Document Document::fromBsonWithMetaData(const BSONObj& bson) {
diff --git a/src/mongo/db/exec/document_value/document.h b/src/mongo/db/exec/document_value/document.h
index ba4a50481bc..062778628a0 100644
--- a/src/mongo/db/exec/document_value/document.h
+++ b/src/mongo/db/exec/document_value/document.h
@@ -102,6 +102,7 @@ public:
     static constexpr StringData metaFieldSearchScoreDetails = "$searchScoreDetails"_sd;
     static constexpr StringData metaFieldSearchSortValues = "$searchSortValues"_sd;
     static constexpr StringData metaFieldIndexKey = "$indexKey"_sd;
+    static constexpr StringData metaFieldVectorSearchScore = "$vectorSearchScore"_sd;
 
     static const StringDataSet allMetadataFieldNames;
 
diff --git a/src/mongo/db/exec/document_value/document_metadata_fields.cpp b/src/mongo/db/exec/document_value/document_metadata_fields.cpp
index d33eee6c140..0532ed2e8cb 100644
--- a/src/mongo/db/exec/document_value/document_metadata_fields.cpp
+++ b/src/mongo/db/exec/document_value/document_metadata_fields.cpp
@@ -96,6 +96,9 @@ void DocumentMetadataFields::mergeWith(const DocumentMetadataFields& other) {
     if (!hasSearchSortValues() && other.hasSearchSortValues()) {
         setSearchSortValues(other.getSearchSortValues());
     }
+    if (!hasVectorSearchScore() && other.hasVectorSearchScore()) {
+        setVectorSearchScore(other.getVectorSearchScore());
+    }
 }
 
 void DocumentMetadataFields::copyFrom(const DocumentMetadataFields& other) {
@@ -135,6 +138,9 @@ void DocumentMetadataFields::copyFrom(const DocumentMetadataFields& other) {
     if (other.hasSearchSortValues()) {
         setSearchSortValues(other.getSearchSortValues());
     }
+    if (other.hasVectorSearchScore()) {
+        setVectorSearchScore(other.getVectorSearchScore());
+    }
 }
 
 size_t DocumentMetadataFields::getApproximateSize() const {
@@ -216,6 +222,10 @@ void DocumentMetadataFields::serializeForSorter(BufBuilder& buf) const {
         buf.appendNum(static_cast<char>(MetaType::kSearchSortValues + 1));
         getSearchSortValues().appendSelfToBufBuilder(buf);
     }
+    if (hasVectorSearchScore()) {
+        buf.appendNum(static_cast<char>(MetaType::kVectorSearchScore + 1));
+        buf.appendNum(getVectorSearchScore());
+    }
     buf.appendNum(static_cast<char>(0));
 }
 
@@ -256,6 +266,8 @@ void DocumentMetadataFields::deserializeForSorter(BufReader& buf, DocumentMetada
         } else if (marker == static_cast<char>(MetaType::kSearchSortValues) + 1) {
             out->setSearchSortValues(
                 BSONObj::deserializeForSorter(buf, BSONObj::SorterDeserializeSettings()));
+        } else if (marker == static_cast<char>(MetaType::kVectorSearchScore) + 1) {
+            out->setVectorSearchScore(buf.read<LittleEndian<double>>());
         } else {
             uasserted(28744, "Unrecognized marker, unable to deserialize buffer");
         }
@@ -317,6 +329,8 @@ const char* DocumentMetadataFields::typeNameToDebugString(DocumentMetadataFields
             return "timeseries bucket max time";
         case DocumentMetadataFields::kSearchSortValues:
             return "$search sort values";
+        case DocumentMetadataFields::kVectorSearchScore:
+            return "$vectorSearch distance";
         default:
             MONGO_UNREACHABLE;
     }
diff --git a/src/mongo/db/exec/document_value/document_metadata_fields.h b/src/mongo/db/exec/document_value/document_metadata_fields.h
index ede2f73229d..e8451677ea7 100644
--- a/src/mongo/db/exec/document_value/document_metadata_fields.h
+++ b/src/mongo/db/exec/document_value/document_metadata_fields.h
@@ -68,6 +68,7 @@ public:
         kTimeseriesBucketMinTime,
         kTimeseriesBucketMaxTime,
         kSearchSortValues,
+        kVectorSearchScore,
 
         // New fields must be added before the kNumFields sentinel.
         kNumFields
@@ -330,6 +331,20 @@ public:
         _holder->searchSortValues = vals.getOwned();
     }
 
+    bool hasVectorSearchScore() const {
+        return _holder && _holder->metaFields.test(MetaType::kVectorSearchScore);
+    }
+
+    double getVectorSearchScore() const {
+        tassert(7828400, "vectorSearchScore must be present in metadata", hasVectorSearchScore());
+        return _holder->vectorSearchScore;
+    }
+
+    void setVectorSearchScore(double vectorSearchScore) {
+        _setCommon(MetaType::kVectorSearchScore);
+        _holder->vectorSearchScore = vectorSearchScore;
+    }
+
     void serializeForSorter(BufBuilder& buf) const;
 
     bool isModified() const {
@@ -376,6 +391,7 @@ private:
         Date_t timeseriesBucketMinTime;
         Date_t timeseriesBucketMaxTime;
         BSONObj searchSortValues;
+        double vectorSearchScore{0.0};
     };
 
     // Null until the first setter is called, at which point a MetadataHolder struct is allocated.
diff --git a/src/mongo/db/exec/document_value/document_metadata_fields_test.cpp b/src/mongo/db/exec/document_value/document_metadata_fields_test.cpp
index 4a76154f1f6..23ab2277c96 100644
--- a/src/mongo/db/exec/document_value/document_metadata_fields_test.cpp
+++ b/src/mongo/db/exec/document_value/document_metadata_fields_test.cpp
@@ -52,6 +52,7 @@ TEST(DocumentMetadataFieldsTest, AllMetadataRoundtripsThroughSerialization) {
     metadata.setSearchScoreDetails(BSON("scoreDetails"
                                         << "foo"));
     metadata.setSearchSortValues(BSON("a" << 1));
+    metadata.setVectorSearchScore(7.6);
 
     BufBuilder builder;
     metadata.serializeForSorter(builder);
@@ -72,6 +73,7 @@ TEST(DocumentMetadataFieldsTest, AllMetadataRoundtripsThroughSerialization) {
                       BSON("scoreDetails"
                            << "foo"));
     ASSERT_BSONOBJ_EQ(deserialized.getSearchSortValues(), BSON("a" << 1));
+    ASSERT_EQ(deserialized.getVectorSearchScore(), 7.6);
 }
 
 TEST(DocumentMetadataFieldsTest, HasMethodsReturnFalseForEmptyMetadata) {
@@ -87,6 +89,7 @@ TEST(DocumentMetadataFieldsTest, HasMethodsReturnFalseForEmptyMetadata) {
     ASSERT_FALSE(metadata.hasIndexKey());
     ASSERT_FALSE(metadata.hasSearchScoreDetails());
     ASSERT_FALSE(metadata.hasSearchSortValues());
+    ASSERT_FALSE(metadata.hasVectorSearchScore());
 }
 
 TEST(DocumentMetadataFieldsTest, HasMethodsReturnTrueForInitializedMetadata) {
@@ -133,6 +136,10 @@ TEST(DocumentMetadataFieldsTest, HasMethodsReturnTrueForInitializedMetadata) {
     ASSERT_FALSE(metadata.hasSearchSortValues());
     metadata.setSearchSortValues(BSON("a" << 1));
     ASSERT_TRUE(metadata.hasSearchSortValues());
+
+    ASSERT_FALSE(metadata.hasVectorSearchScore());
+    metadata.setVectorSearchScore(7.6);
+    ASSERT_TRUE(metadata.hasVectorSearchScore());
 }
 
 TEST(DocumentMetadataFieldsTest, MoveConstructor) {
@@ -148,6 +155,7 @@ TEST(DocumentMetadataFieldsTest, MoveConstructor) {
     metadata.setSearchScoreDetails(BSON("scoreDetails"
                                         << "foo"));
     metadata.setSearchSortValues(BSON("a" << 1));
+    metadata.setVectorSearchScore(7.6);
 
     DocumentMetadataFields moveConstructed(std::move(metadata));
     ASSERT_TRUE(moveConstructed);
@@ -164,6 +172,7 @@ TEST(DocumentMetadataFieldsTest, MoveConstructor) {
                       BSON("scoreDetails"
                            << "foo"));
     ASSERT_BSONOBJ_EQ(moveConstructed.getSearchSortValues(), BSON("a" << 1));
+    ASSERT_EQ(moveConstructed.getVectorSearchScore(), 7.6);
 
     ASSERT_FALSE(metadata);  // NOLINT(bugprone-use-after-move)
 }
@@ -181,6 +190,7 @@ TEST(DocumentMetadataFieldsTest, MoveAssignmentOperator) {
     metadata.setSearchScoreDetails(BSON("scoreDetails"
                                         << "foo"));
     metadata.setSearchSortValues(BSON("a" << 1));
+    metadata.setVectorSearchScore(7.6);
 
     DocumentMetadataFields moveAssigned;
     moveAssigned.setTextScore(12.3);
@@ -200,6 +210,7 @@ TEST(DocumentMetadataFieldsTest, MoveAssignmentOperator) {
                       BSON("scoreDetails"
                            << "foo"));
     ASSERT_BSONOBJ_EQ(moveAssigned.getSearchSortValues(), BSON("a" << 1));
+    ASSERT_EQ(moveAssigned.getVectorSearchScore(), 7.6);
 
     ASSERT_FALSE(metadata);  // NOLINT(bugprone-use-after-move)
 }
@@ -254,6 +265,7 @@ TEST(DocumentMetadataFieldsTest, MergeWithOnlyCopiesMetadataThatDestinationDoesN
     ASSERT_FALSE(destination.hasIndexKey());
     ASSERT_FALSE(destination.hasSearchScoreDetails());
     ASSERT_FALSE(destination.hasSearchSortValues());
+    ASSERT_FALSE(destination.hasVectorSearchScore());
 }
 
 TEST(DocumentMetadataFieldsTest, CopyFromCopiesAllMetadataThatSourceHas) {
@@ -280,6 +292,7 @@ TEST(DocumentMetadataFieldsTest, CopyFromCopiesAllMetadataThatSourceHas) {
     ASSERT_FALSE(destination.hasIndexKey());
     ASSERT_FALSE(destination.hasSearchScoreDetails());
     ASSERT_FALSE(destination.hasSearchSortValues());
+    ASSERT_FALSE(destination.hasVectorSearchScore());
 }
 
 TEST(DocumentMetadataFieldsTest, GetTimeseriesBucketMinTimeExists) {
@@ -323,6 +336,7 @@ TEST(DocumentMetadataFieldsTest, MetadataIsMarkedModifiedOnSetMetadataField) {
     testFieldSetter([](DocumentMetadataFields& md) { md.setTimeseriesBucketMinTime(Date_t()); });
     testFieldSetter([](DocumentMetadataFields& md) { md.setTimeseriesBucketMaxTime(Date_t()); });
     testFieldSetter([](DocumentMetadataFields& md) { md.setSearchSortValues(BSON("a" << 1)); });
+    testFieldSetter([](DocumentMetadataFields& md) { md.setVectorSearchScore(60.0); });
 }
 
 TEST(DocumentMetadataFieldsTest, MetadataIsConstructedUnmodified) {
diff --git a/src/mongo/db/exec/document_value/document_value_test.cpp b/src/mongo/db/exec/document_value/document_value_test.cpp
index 1b5c833f88b..ecc550f6ee0 100644
--- a/src/mongo/db/exec/document_value/document_value_test.cpp
+++ b/src/mongo/db/exec/document_value/document_value_test.cpp
@@ -907,7 +907,7 @@ TEST(MetaFields, CopyMetadataFromCopiesAllMetadata) {
                  << "h" << 1 << "$indexKey" << BSON("y" << 1) << "$searchScoreDetails"
                  << BSON("scoreDetails"
                          << "foo")
-                 << "$searchSortValues" << BSON("a" << 1)));
+                 << "$searchSortValues" << BSON("a" << 1) << "$vectorSearchScore" << 6.7));
 
     MutableDocument destination{};
     destination.copyMetaDataFrom(source);
@@ -925,6 +925,7 @@ TEST(MetaFields, CopyMetadataFromCopiesAllMetadata) {
                       BSON("scoreDetails"
                            << "foo"));
     ASSERT_BSONOBJ_EQ(result.metadata().getSearchSortValues(), BSON("a" << 1));
+    ASSERT_EQ(result.metadata().getVectorSearchScore(), 6.7);
 }
 
 class SerializationTest : public unittest::Test {
@@ -945,6 +946,8 @@ protected:
         ASSERT_EQ(output.metadata().hasSearchScore(), input.metadata().hasSearchScore());
         ASSERT_EQ(output.metadata().hasSearchHighlights(), input.metadata().hasSearchHighlights());
         ASSERT_EQ(output.metadata().hasIndexKey(), input.metadata().hasIndexKey());
+        ASSERT_EQ(output.metadata().hasVectorSearchScore(),
+                  input.metadata().hasVectorSearchScore());
         if (input.metadata().hasTextScore()) {
             ASSERT_EQ(output.metadata().getTextScore(), input.metadata().getTextScore());
         }
@@ -965,6 +968,10 @@ protected:
             ASSERT_BSONOBJ_EQ(output.metadata().getSearchScoreDetails(),
                               input.metadata().getSearchScoreDetails());
         }
+        if (input.metadata().hasVectorSearchScore()) {
+            ASSERT_EQ(output.metadata().getVectorSearchScore(),
+                      input.metadata().getVectorSearchScore());
+        }
 
         ASSERT(output.toBson().binaryEqual(input.toBson()));
     }
@@ -979,6 +986,7 @@ TEST_F(SerializationTest, MetaSerializationNoVals) {
                                                         << "def"_sd));
     docBuilder.metadata().setSearchScoreDetails(BSON("scoreDetails"
                                                      << "foo"));
+    docBuilder.metadata().setVectorSearchScore(40.0);
     assertRoundTrips(docBuilder.freeze());
 }
 
@@ -993,6 +1001,7 @@ TEST_F(SerializationTest, MetaSerializationWithVals) {
     docBuilder.metadata().setIndexKey(BSON("key" << 42));
     docBuilder.metadata().setSearchScoreDetails(BSON("scoreDetails"
                                                      << "foo"));
+    docBuilder.metadata().setVectorSearchScore(40.0);
     assertRoundTrips(docBuilder.freeze());
 }
 
@@ -1016,6 +1025,7 @@ TEST(MetaFields, ToAndFromBson) {
     docBuilder.metadata().setSearchScoreDetails(BSON("scoreDetails"
                                                      << "foo"));
     docBuilder.metadata().setSearchSortValues(BSON("a" << 42));
+    docBuilder.metadata().setVectorSearchScore(40.0);
     Document doc = docBuilder.freeze();
     BSONObj obj = doc.toBsonWithMetaData();
     ASSERT_EQ(10.0, obj[Document::metaFieldTextScore].Double());
@@ -1028,6 +1038,7 @@ TEST(MetaFields, ToAndFromBson) {
                       BSON("scoreDetails"
                            << "foo"));
     ASSERT_BSONOBJ_EQ(BSON("a" << 42), obj[Document::metaFieldSearchSortValues].Obj());
+    ASSERT_EQ(40.0, obj[Document::metaFieldVectorSearchScore].Double());
     Document fromBson = Document::fromBsonWithMetaData(obj);
     ASSERT_TRUE(fromBson.metadata().hasTextScore());
     ASSERT_TRUE(fromBson.metadata().hasRandVal());
@@ -1037,6 +1048,7 @@ TEST(MetaFields, ToAndFromBson) {
                            << "foo"),
                       fromBson.metadata().getSearchScoreDetails());
     ASSERT_BSONOBJ_EQ(BSON("a" << 42), fromBson.metadata().getSearchSortValues());
+    ASSERT_EQ(40.0, fromBson.metadata().getVectorSearchScore());
 }
 
 TEST(MetaFields, ToAndFromBsonTrivialConvertibility) {
diff --git a/src/mongo/db/exec/exclusion_projection_executor_test.cpp b/src/mongo/db/exec/exclusion_projection_executor_test.cpp
index 983c5e1995a..c3866ef865f 100644
--- a/src/mongo/db/exec/exclusion_projection_executor_test.cpp
+++ b/src/mongo/db/exec/exclusion_projection_executor_test.cpp
@@ -363,7 +363,8 @@ TEST(ExclusionProjectionExecutionTest, ShouldEvaluateMetaExpressions) {
                                                             "i: {$meta: 'recordId'}, "
                                                             "j: {$meta: 'indexKey'}, "
                                                             "k: {$meta: 'sortKey'}, "
-                                                            "l: {$meta: 'searchScoreDetails'}}"));
+                                                            "l: {$meta: 'searchScoreDetails'}, "
+                                                            "m: {$meta: 'vectorSearchScore'}}"));
 
     MutableDocument inputDocBuilder(Document{{"a", 1}, {"b", 2}});
     inputDocBuilder.metadata().setTextScore(0.0);
@@ -377,6 +378,7 @@ TEST(ExclusionProjectionExecutionTest, ShouldEvaluateMetaExpressions) {
     inputDocBuilder.metadata().setSortKey(Value{Document{{"bar", 8}}}, true);
     inputDocBuilder.metadata().setSearchScoreDetails(BSON("scoreDetails"
                                                           << "foo"));
+    inputDocBuilder.metadata().setVectorSearchScore(9.0);
     Document inputDoc = inputDocBuilder.freeze();
 
     auto result = exclusion->applyTransformation(inputDoc);
@@ -384,7 +386,7 @@ TEST(ExclusionProjectionExecutionTest, ShouldEvaluateMetaExpressions) {
     ASSERT_DOCUMENT_EQ(result,
                        Document{fromjson("{b: 2, c: 0.0, d: 1.0, e: 2.0, f: 'foo', g: 3.0, "
                                          "h: [4, 5], i: 6, j: {foo: 7}, k: [{bar: 8}],"
-                                         "l: {scoreDetails: 'foo'}}")});
+                                         "l: {scoreDetails: 'foo'}, m: 9.0}")});
 }
 
 TEST(ExclusionProjectionExecutionTest, ShouldAddMetaExpressionsToDependencies) {
@@ -398,18 +400,20 @@ TEST(ExclusionProjectionExecutionTest, ShouldAddMetaExpressionsToDependencies) {
                                                             "i: {$meta: 'recordId'}, "
                                                             "j: {$meta: 'indexKey'}, "
                                                             "k: {$meta: 'sortKey'}, "
-                                                            "l: {$meta: 'searchScoreDetails'}}"));
+                                                            "l: {$meta: 'searchScoreDetails'}}, "
+                                                            "m: {$meta: 'vectorSearchScore'}"));
 
     DepsTracker deps;
     exclusion->addDependencies(&deps);
 
     ASSERT_EQ(deps.fields.size(), 0UL);
 
-    // We do not add the dependencies for searchScore, searchHighlights, or searchScoreDetails
-    // because those values are not stored in the collection (or in mongod at all).
+    // We do not add the dependencies for searchScore, searchHighlights, searchScoreDetails, or
+    // distance because those values are not stored in the collection (or in mongod at all).
     ASSERT_FALSE(deps.metadataDeps()[DocumentMetadataFields::kSearchScore]);
     ASSERT_FALSE(deps.metadataDeps()[DocumentMetadataFields::kSearchHighlights]);
     ASSERT_FALSE(deps.metadataDeps()[DocumentMetadataFields::kSearchScoreDetails]);
+    ASSERT_FALSE(deps.metadataDeps()[DocumentMetadataFields::kVectorSearchScore]);
 
     ASSERT_TRUE(deps.metadataDeps()[DocumentMetadataFields::kTextScore]);
     ASSERT_TRUE(deps.metadataDeps()[DocumentMetadataFields::kRandVal]);
diff --git a/src/mongo/db/exec/inclusion_projection_executor_test.cpp b/src/mongo/db/exec/inclusion_projection_executor_test.cpp
index 53ebf3af4a3..b31899043ca 100644
--- a/src/mongo/db/exec/inclusion_projection_executor_test.cpp
+++ b/src/mongo/db/exec/inclusion_projection_executor_test.cpp
@@ -814,18 +814,20 @@ TEST_F(InclusionProjectionExecutionTestWithFallBackToDefault,
                                                             "i: {$meta: 'recordId'}, "
                                                             "j: {$meta: 'indexKey'}, "
                                                             "k: {$meta: 'sortKey'}, "
-                                                            "l: {$meta: 'searchScoreDetails'}}"));
+                                                            "l: {$meta: 'searchScoreDetails'}}, "
+                                                            "m: {$meta: 'vectorSearchScore'}"));
 
     DepsTracker deps;
     inclusion->addDependencies(&deps);
 
     ASSERT_EQ(deps.fields.size(), 2UL);
 
-    // We do not add the dependencies for searchScore, searchHighlights, or searchScoreDetails
-    // because those values are not stored in the collection (or in mongod at all).
+    // We do not add the dependencies for searchScore, searchHighlights, searchScoreDetails, or
+    // distance because those values are not stored in the collection (or in mongod at all).
     ASSERT_FALSE(deps.metadataDeps()[DocumentMetadataFields::kSearchScore]);
     ASSERT_FALSE(deps.metadataDeps()[DocumentMetadataFields::kSearchHighlights]);
     ASSERT_FALSE(deps.metadataDeps()[DocumentMetadataFields::kSearchScoreDetails]);
+    ASSERT_FALSE(deps.metadataDeps()[DocumentMetadataFields::kVectorSearchScore]);
 
     ASSERT_TRUE(deps.metadataDeps()[DocumentMetadataFields::kTextScore]);
     ASSERT_TRUE(deps.metadataDeps()[DocumentMetadataFields::kRandVal]);
@@ -847,7 +849,8 @@ TEST_F(InclusionProjectionExecutionTestWithFallBackToDefault, ShouldEvaluateMeta
                                                             "i: {$meta: 'recordId'}, "
                                                             "j: {$meta: 'indexKey'}, "
                                                             "k: {$meta: 'sortKey'}, "
-                                                            "l: {$meta: 'searchScoreDetails'}}"));
+                                                            "l: {$meta: 'searchScoreDetails'}, "
+                                                            "m: {$meta: 'vectorSearchScore'}}"));
 
     MutableDocument inputDocBuilder(Document{{"a", 1}});
     inputDocBuilder.metadata().setTextScore(0.0);
@@ -861,6 +864,7 @@ TEST_F(InclusionProjectionExecutionTestWithFallBackToDefault, ShouldEvaluateMeta
     inputDocBuilder.metadata().setSortKey(Value{Document{{"bar", 8}}}, true);
     inputDocBuilder.metadata().setSearchScoreDetails(BSON("scoreDetails"
                                                           << "foo"));
+    inputDocBuilder.metadata().setVectorSearchScore(9.0);
     Document inputDoc = inputDocBuilder.freeze();
 
     auto result = inclusion->applyTransformation(inputDoc);
@@ -868,7 +872,7 @@ TEST_F(InclusionProjectionExecutionTestWithFallBackToDefault, ShouldEvaluateMeta
     ASSERT_DOCUMENT_EQ(result,
                        Document{fromjson("{a: 1, c: 0.0, d: 1.0, e: 2.0, f: 'foo', g: 3.0, "
                                          "h: [4, 5], i: 6, j: {foo: 7}, k: [{bar: 8}], "
-                                         "l: {scoreDetails: 'foo'}}")});
+                                         "l: {scoreDetails: 'foo'}, m: 9.0}")});
 }
 
 //
diff --git a/src/mongo/db/pipeline/expression.cpp b/src/mongo/db/pipeline/expression.cpp
index 21542dd0e48..ecb1f2382de 100644
--- a/src/mongo/db/pipeline/expression.cpp
+++ b/src/mongo/db/pipeline/expression.cpp
@@ -3092,9 +3092,11 @@ const std::string sortKeyName = "sortKey";
 const std::string searchScoreDetailsName = "searchScoreDetails";
 const std::string timeseriesBucketMinTimeName = "timeseriesBucketMinTime";
 const std::string timeseriesBucketMaxTimeName = "timeseriesBucketMaxTime";
+const std::string vectorSearchScoreName = "vectorSearchScore";
 
 using MetaType = DocumentMetadataFields::MetaType;
 const StringMap<DocumentMetadataFields::MetaType> kMetaNameToMetaType = {
+    {vectorSearchScoreName, MetaType::kVectorSearchScore},
     {geoNearDistanceName, MetaType::kGeoNearDist},
     {geoNearPointName, MetaType::kGeoNearPoint},
     {indexKeyName, MetaType::kIndexKey},
@@ -3110,6 +3112,7 @@ const StringMap<DocumentMetadataFields::MetaType> kMetaNameToMetaType = {
 };
 
 const stdx::unordered_map<DocumentMetadataFields::MetaType, StringData> kMetaTypeToMetaName = {
+    {MetaType::kVectorSearchScore, vectorSearchScoreName},
     {MetaType::kGeoNearDist, geoNearDistanceName},
     {MetaType::kGeoNearPoint, geoNearPointName},
     {MetaType::kIndexKey, indexKeyName},
@@ -3153,6 +3156,9 @@ Value ExpressionMeta::serialize(bool explain) const {
 Value ExpressionMeta::evaluate(const Document& root, Variables* variables) const {
     const auto& metadata = root.metadata();
     switch (_metaType) {
+        case MetaType::kVectorSearchScore:
+            return metadata.hasVectorSearchScore() ? Value(metadata.getVectorSearchScore())
+                                                   : Value();
         case MetaType::kTextScore:
             return metadata.hasTextScore() ? Value(metadata.getTextScore()) : Value();
         case MetaType::kRandVal:
diff --git a/src/mongo/db/pipeline/expression_test.cpp b/src/mongo/db/pipeline/expression_test.cpp
index b8c4cf6266a..03fc4d3b663 100644
--- a/src/mongo/db/pipeline/expression_test.cpp
+++ b/src/mongo/db/pipeline/expression_test.cpp
@@ -3161,6 +3161,18 @@ TEST(ExpressionMetaTest, ExpressionMetaSearchScoreDetails) {
     Value val = expressionMeta->evaluate(doc.freeze(), &expCtx.variables);
     ASSERT_DOCUMENT_EQ(val.getDocument(), Document(details));
 }
+
+TEST(ExpressionMetaTest, ExpressionMetaVectorSearchScore) {
+    auto expCtx = ExpressionContextForTest{};
+    BSONObj expr = fromjson("{$meta: \"vectorSearchScore\"}");
+    auto expressionMeta =
+        ExpressionMeta::parse(&expCtx, expr.firstElement(), expCtx.variablesParseState);
+
+    MutableDocument doc;
+    doc.metadata().setVectorSearchScore(1.23);
+    Value val = expressionMeta->evaluate(doc.freeze(), &expCtx.variables);
+    ASSERT_EQ(val.getDouble(), 1.23);
+}
 }  // namespace expression_meta_test
 
 namespace ExpressionRegexTest {
diff --git a/src/mongo/db/query/query_feature_flags.idl b/src/mongo/db/query/query_feature_flags.idl
index 18cb4dfedc9..81f89c97997 100644
--- a/src/mongo/db/query/query_feature_flags.idl
+++ b/src/mongo/db/query/query_feature_flags.idl
@@ -157,3 +157,8 @@ feature_flags:
       cpp_varname: gFeatureFlagSearchBatchSizeLimit
       default: true
       version: 6.0
+
+    featureFlagVectorSearchPublicPreview:
+      description: "Feature flag to enable vector search for public preview."
+      cpp_varname: gFeatureFlagVectorSearchPublicPreview
+      default: false