diff --git a/src/MongoDB.Driver/Core/Misc/Feature.cs b/src/MongoDB.Driver/Core/Misc/Feature.cs
index 720cf3c19db..afdc126f9c7 100644
--- a/src/MongoDB.Driver/Core/Misc/Feature.cs
+++ b/src/MongoDB.Driver/Core/Misc/Feature.cs
@@ -91,6 +91,7 @@ public class Feature
private static readonly Feature __setWindowFields = new Feature("SetWindowFields", WireVersion.Server50);
private static readonly Feature __setWindowFieldsLocf = new Feature("SetWindowFieldsLocf", WireVersion.Server52);
private static readonly Feature __shardedTransactions = new Feature("ShardedTransactions", WireVersion.Server42);
+ private static readonly Feature __sigmoidOperator = new Feature("SigmoidOperator", WireVersion.Server81);
private static readonly Feature __snapshotReads = new Feature("SnapshotReads", WireVersion.Server50, notSupportedMessage: "Snapshot reads require MongoDB 5.0 or later");
private static readonly Feature __sortArrayOperator = new Feature("SortArrayOperator", WireVersion.Server52);
private static readonly Feature __speculativeAuthentication = new Feature("SpeculativeAuthentication", WireVersion.Server44);
@@ -431,6 +432,11 @@ public class Feature
///
public static Feature ShardedTransactions => __shardedTransactions;
+ ///
+ /// Gets the $sigmoid operator feature.
+ ///
+ public static Feature SigmoidOperator => __sigmoidOperator;
+
///
/// Gets the snapshot reads feature.
///
diff --git a/src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Expressions/AstUnaryOperator.cs b/src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Expressions/AstUnaryOperator.cs
index a712962ae69..17422736971 100644
--- a/src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Expressions/AstUnaryOperator.cs
+++ b/src/MongoDB.Driver/Linq/Linq3Implementation/Ast/Expressions/AstUnaryOperator.cs
@@ -58,6 +58,7 @@ internal enum AstUnaryOperator
Round,
SetIntersection,
SetUnion,
+ Sigmoid,
Sin,
Sinh,
Size,
@@ -161,6 +162,7 @@ public static string Render(this AstUnaryOperator @operator)
AstUnaryOperator.Round => "$round",
AstUnaryOperator.SetIntersection => "$setIntersection",
AstUnaryOperator.SetUnion => "$setUnion",
+ AstUnaryOperator.Sigmoid => "$sigmoid",
AstUnaryOperator.Sin => "$sin",
AstUnaryOperator.Sinh => "$sinh",
AstUnaryOperator.Size => "$size",
diff --git a/src/MongoDB.Driver/Linq/Linq3Implementation/Reflection/MqlMethod.cs b/src/MongoDB.Driver/Linq/Linq3Implementation/Reflection/MqlMethod.cs
index e04f8d50d13..be28eece135 100644
--- a/src/MongoDB.Driver/Linq/Linq3Implementation/Reflection/MqlMethod.cs
+++ b/src/MongoDB.Driver/Linq/Linq3Implementation/Reflection/MqlMethod.cs
@@ -33,6 +33,7 @@ internal static class MqlMethod
private static readonly MethodInfo __field;
private static readonly MethodInfo __isMissing;
private static readonly MethodInfo __isNullOrMissing;
+ private static readonly MethodInfo __sigmoid;
// static constructor
static MqlMethod()
@@ -47,6 +48,7 @@ static MqlMethod()
__field = ReflectionInfo.Method((object container, string fieldName, IBsonSerializer