diff --git a/src/Nest/Ingest/Processors/AppendProcessor.cs b/src/Nest/Ingest/Processors/AppendProcessor.cs
index 0e09befb585..cfd0de25d1a 100644
--- a/src/Nest/Ingest/Processors/AppendProcessor.cs
+++ b/src/Nest/Ingest/Processors/AppendProcessor.cs
@@ -20,12 +20,17 @@ public interface IAppendProcessor : IProcessor
 
 		[DataMember(Name ="value")]
 		IEnumerable<object> Value { get; set; }
+
+		[DataMember(Name = "allow_duplicates")]
+		bool? AllowDuplicates { get; set; }
 	}
 
 	public class AppendProcessor : ProcessorBase, IAppendProcessor
 	{
 		public Field Field { get; set; }
 		public IEnumerable<object> Value { get; set; }
+		public bool? AllowDuplicates { get; set; }
+
 		protected override string Name => "append";
 	}
 
@@ -35,6 +40,7 @@ public class AppendProcessorDescriptor<T> : ProcessorDescriptorBase<AppendProces
 		protected override string Name => "append";
 		Field IAppendProcessor.Field { get; set; }
 		IEnumerable<object> IAppendProcessor.Value { get; set; }
+		bool? IAppendProcessor.AllowDuplicates { get; set; }
 
 		public AppendProcessorDescriptor<T> Field(Field field) => Assign(field, (a, v) => a.Field = v);
 
@@ -49,5 +55,7 @@ public AppendProcessorDescriptor<T> Value<TValue>(params TValue[] values) => Ass
 				a.Value = (v.First() as IEnumerable)?.Cast<object>();
 			else a.Value = v?.Cast<object>();
 		});
+
+		public AppendProcessorDescriptor<T> AllowDuplicates(bool allowDuplicates = true) => Assign(allowDuplicates, (a, v) => a.AllowDuplicates = v);
 	}
 }
diff --git a/tests/Tests/Ingest/ProcessorAssertions.cs b/tests/Tests/Ingest/ProcessorAssertions.cs
index 049587af294..0d5f221bc47 100644
--- a/tests/Tests/Ingest/ProcessorAssertions.cs
+++ b/tests/Tests/Ingest/ProcessorAssertions.cs
@@ -9,6 +9,7 @@
 using Elastic.Elasticsearch.Xunit.XunitPlumbing;
 using Nest;
 using Tests.Core.Client;
+using Tests.Core.Extensions;
 using Tests.Core.Xunit;
 using Tests.Domain;
 
@@ -59,19 +60,41 @@ public static IPromise<IList<IProcessor>> Fluent(ProcessorsDescriptor d)
 
 		public class Append : ProcessorAssertion
 		{
-			public override Func<ProcessorsDescriptor, IPromise<IList<IProcessor>>> Fluent => d => d
-				.Append<Project>(a => a
-					.Field(p => p.State)
-					.Value(StateOfBeing.Stable, StateOfBeing.VeryActive)
-				);
+			public override Func<ProcessorsDescriptor, IPromise<IList<IProcessor>>> Fluent =>
+				d => d.Append<Project>(a =>
+				{
+					var apd = a.Field(p => p.State).Value(StateOfBeing.Stable, StateOfBeing.VeryActive);
 
-			public override IProcessor Initializer => new AppendProcessor
+					if (TestClient.Configuration.InRange(">=7.11.0"))
+						apd.AllowDuplicates(false);
+
+					return apd;
+				});
+
+			public override IProcessor Initializer
 			{
-				Field = "state",
-				Value = new object[] { StateOfBeing.Stable, StateOfBeing.VeryActive }
-			};
+				get
+				{
+					var ap = new AppendProcessor { Field = "state", Value = new object[] { StateOfBeing.Stable, StateOfBeing.VeryActive } };
+
+					if (TestClient.Configuration.InRange(">=7.11.0"))
+						ap.AllowDuplicates = false;
+
+					return ap;
+				}
+			}
+
+			public override object Json
+			{
+				get
+				{
+					if (TestClient.Configuration.InRange(">=7.11.0"))
+						return new { field = "state", value = new[] { "Stable", "VeryActive" }, allow_duplicates = false };
+
+					return new { field = "state", value = new[] { "Stable", "VeryActive" } };
+				}
+			}
 
-			public override object Json => new { field = "state", value = new[] { "Stable", "VeryActive" } };
 			public override string Key => "append";
 		}