diff --git a/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/src/Providers/MrwSerializationTypeDefinition.cs b/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/src/Providers/MrwSerializationTypeDefinition.cs
index 249dd6a1b13..ae2f057c709 100644
--- a/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/src/Providers/MrwSerializationTypeDefinition.cs
+++ b/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/src/Providers/MrwSerializationTypeDefinition.cs
@@ -26,7 +26,6 @@ namespace Microsoft.Generator.CSharp.ClientModel.Providers
     /// </summary>
     internal class MrwSerializationTypeDefinition : TypeProvider
     {
-        private const string PrivateAdditionalPropertiesPropertyDescription = "Keeps track of any properties unknown to the library.";
         private const string PrivateAdditionalPropertiesPropertyName = "_serializedAdditionalRawData";
         private const string JsonModelWriteCoreMethodName = "JsonModelWriteCore";
         private const string JsonModelCreateCoreMethodName = "JsonModelCreateCore";
@@ -34,7 +33,6 @@ internal class MrwSerializationTypeDefinition : TypeProvider
         private const string PersistableModelCreateCoreMethodName = "PersistableModelCreateCore";
         private const string WriteAction = "writing";
         private const string ReadAction = "reading";
-        private const string AdditionalRawDataVarName = "serializedAdditionalRawData";
         private readonly ParameterProvider _utf8JsonWriterParameter = new("writer", $"The JSON writer.", typeof(Utf8JsonWriter));
         private readonly ParameterProvider _utf8JsonReaderParameter = new("reader", $"The JSON reader.", typeof(Utf8JsonReader), isRef: true);
         private readonly ParameterProvider _serializationOptionsParameter =
@@ -46,22 +44,19 @@ internal class MrwSerializationTypeDefinition : TypeProvider
         private readonly ScopedApi<ModelReaderWriterOptions> _mrwOptionsParameterSnippet;
         private readonly ScopedApi<JsonElement> _jsonElementParameterSnippet;
         private readonly ScopedApi<bool> _isNotEqualToWireConditionSnippet;
-        private readonly CSharpType _privateAdditionalRawDataPropertyType = typeof(IDictionary<string, BinaryData>);
         private readonly CSharpType _jsonModelTInterface;
         private readonly CSharpType? _jsonModelObjectInterface;
         private readonly CSharpType _persistableModelTInterface;
         private readonly CSharpType? _persistableModelObjectInterface;
-        private TypeProvider _model;
+        private readonly ModelProvider _model;
         private readonly InputModelType _inputModel;
         private readonly FieldProvider? _rawDataField;
         private readonly bool _isStruct;
         private ConstructorProvider? _serializationConstructor;
         // Flag to determine if the model should override the serialization methods
         private readonly bool _shouldOverrideMethods;
-        // TODO -- we should not be needing this if we resolve https://github.com/microsoft/typespec/issues/3796
-        private readonly MrwSerializationTypeDefinition? _baseSerializationProvider;
 
-        public MrwSerializationTypeDefinition(InputModelType inputModel, TypeProvider modelProvider)
+        public MrwSerializationTypeDefinition(InputModelType inputModel, ModelProvider modelProvider)
         {
             _model = modelProvider;
             _inputModel = inputModel;
@@ -71,11 +66,7 @@ public MrwSerializationTypeDefinition(InputModelType inputModel, TypeProvider mo
             _jsonModelObjectInterface = _isStruct ? (CSharpType)typeof(IJsonModel<object>) : null;
             _persistableModelTInterface = new CSharpType(typeof(IPersistableModel<>), _model.Type);
             _persistableModelObjectInterface = _isStruct ? (CSharpType)typeof(IPersistableModel<object>) : null;
-
-            if (inputModel.BaseModel is not null)
-                _baseSerializationProvider = ClientModelPlugin.Instance.TypeFactory.CreateSerializations(inputModel.BaseModel, modelProvider).OfType<MrwSerializationTypeDefinition>().FirstOrDefault();
-
-            _rawDataField = BuildRawDataField();
+            _rawDataField = _model.Fields.FirstOrDefault(f => f.Name == PrivateAdditionalPropertiesPropertyName);
             _shouldOverrideMethods = _model.Type.BaseType != null && _model.Type.BaseType is { IsFrameworkType: false };
             _utf8JsonWriterSnippet = _utf8JsonWriterParameter.As<Utf8JsonWriter>();
             _mrwOptionsParameterSnippet = _serializationOptionsParameter.As<ModelReaderWriterOptions>();
@@ -86,25 +77,15 @@ public MrwSerializationTypeDefinition(InputModelType inputModel, TypeProvider mo
         protected override string GetNamespace() => _model.Type.Namespace;
 
         protected override TypeSignatureModifiers GetDeclarationModifiers() => _model.DeclarationModifiers;
-        private ConstructorProvider SerializationConstructor => _serializationConstructor ??= BuildSerializationConstructor();
+        private ConstructorProvider SerializationConstructor => _serializationConstructor ??= _model.FullConstructor;
 
         protected override string BuildRelativeFilePath() => Path.Combine("src", "Generated", "Models", $"{Name}.Serialization.cs");
 
         protected override string BuildName() => _model.Name;
 
-        /// <summary>
-        /// Builds the fields for the model by adding the raw data field for serialization.
-        /// </summary>
-        /// <returns>The list of <see cref="FieldProvider"/> for the model.</returns>
-        protected override FieldProvider[] BuildFields()
-        {
-            return _rawDataField != null ? [_rawDataField] : Array.Empty<FieldProvider>();
-        }
-
         protected override ConstructorProvider[] BuildConstructors()
         {
             List<ConstructorProvider> constructors = new();
-            bool serializationCtorParamsMatch = false;
             bool ctorWithNoParamsExist = false;
 
             foreach (var ctor in _model.Constructors)
@@ -116,21 +97,6 @@ protected override ConstructorProvider[] BuildConstructors()
                 {
                     ctorWithNoParamsExist = true;
                 }
-
-                if (!serializationCtorParamsMatch)
-                {
-                    // Check if the model constructor parameters match the serialization constructor parameters
-                    if (initializationCtorParams.SequenceEqual(SerializationConstructor.Signature.Parameters))
-                    {
-                        serializationCtorParamsMatch = true;
-                    }
-                }
-            }
-
-            // Add the serialization constructor if it doesn't match any of the existing constructors
-            if (!serializationCtorParamsMatch)
-            {
-                constructors.Add(SerializationConstructor);
             }
 
             // Add an empty constructor if the model doesn't have one
@@ -139,39 +105,7 @@ protected override ConstructorProvider[] BuildConstructors()
                 constructors.Add(BuildEmptyConstructor());
             }
 
-            return constructors.ToArray();
-        }
-
-        /// <summary>
-        /// Builds the raw data field for the model to be used for serialization.
-        /// </summary>
-        /// <returns>The constructed <see cref="FieldProvider"/> if the model should generate the field.</returns>
-        private FieldProvider? BuildRawDataField()
-        {
-            if (_isStruct)
-            {
-                return null;
-            }
-
-            // check if there is a raw data field on my base, if so, we do not have to have one here
-            if (_baseSerializationProvider?._rawDataField != null)
-            {
-                return null;
-            }
-
-            var modifiers = FieldModifiers.Private;
-            if (!_model.DeclarationModifiers.HasFlag(TypeSignatureModifiers.Sealed))
-            {
-                modifiers |= FieldModifiers.Protected;
-            }
-
-            var rawDataField = new FieldProvider(
-                modifiers: modifiers,
-                type: _privateAdditionalRawDataPropertyType,
-                description: FormattableStringHelpers.FromString(PrivateAdditionalPropertiesPropertyDescription),
-                name: PrivateAdditionalPropertiesPropertyName);
-
-            return rawDataField;
+            return [.. constructors];
         }
 
         /// <summary>
@@ -527,28 +461,6 @@ internal MethodProvider BuildPersistableModelGetFormatFromOptionsObjectDeclarati
             );
         }
 
-        /// <summary>
-        /// Builds the serialization constructor for the model.
-        /// </summary>
-        /// <returns>The constructed serialization constructor.</returns>
-        internal ConstructorProvider BuildSerializationConstructor()
-        {
-            var (serializationCtorParameters, serializationCtorInitializer) = BuildSerializationConstructorParameters();
-
-            return new ConstructorProvider(
-                signature: new ConstructorSignature(
-                    Type,
-                    $"Initializes a new instance of {Type:C}",
-                    MethodSignatureModifiers.Internal,
-                    serializationCtorParameters,
-                    Initializer: serializationCtorInitializer),
-                bodyStatements: new MethodBodyStatement[]
-                {
-                    GetPropertyInitializers()
-                },
-                this);
-        }
-
         private MethodBodyStatement[] BuildJsonModelWriteMethodBody(MethodProvider jsonModelWriteCoreMethod)
         {
             var coreMethodSignature = jsonModelWriteCoreMethod.Signature;
@@ -699,7 +611,6 @@ private ValueExpression[] GetSerializationCtorParameterValues()
         {
             var parameters = SerializationConstructor.Signature.Parameters;
             ValueExpression[] serializationCtorParameters = new ValueExpression[parameters.Count];
-            var serializationCtorParameterValues = new Dictionary<string, ValueExpression>(parameters.Count);
 
             // Map property variable names to their corresponding parameter values
             for (int i = 0; i < parameters.Count; i++)
@@ -771,7 +682,7 @@ private List<MethodBodyStatement> BuildDeserializePropertiesStatements(ScopedApi
             // deserialize the raw data properties
             if (_rawDataField != null)
             {
-                var elementType = _privateAdditionalRawDataPropertyType.Arguments[1].FrameworkType;
+                var elementType = _rawDataField.Type.Arguments[1].FrameworkType;
                 var rawDataDeserializationValue = GetValueTypeDeserializationExpression(elementType, jsonProperty.Value(), SerializationFormat.Default);
                 propertyDeserializationStatements.Add(new IfStatement(_isNotEqualToWireConditionSnippet)
                 {
@@ -959,44 +870,6 @@ private static MethodBodyStatement NullCheckCollectionItemIfRequired(
                 ? new IfElseStatement(arrayItemVar.ValueKindEqualsNull(), assignNull, deserializeValue)
                 : deserializeValue;
 
-        /// <summary>
-        /// Builds the parameters for the serialization constructor by iterating through the input model properties.
-        /// It then adds raw data field to the constructor if it doesn't already exist in the list of constructed parameters.
-        /// </summary>
-        /// <returns>The list of parameters for the serialization parameter.</returns>
-        private (IReadOnlyList<ParameterProvider> Parameters, ConstructorInitializer? Initializer) BuildSerializationConstructorParameters()
-        {
-            var baseConstructor = _baseSerializationProvider?.SerializationConstructor.Signature;
-            var baseParameters = baseConstructor?.Parameters ?? [];
-            var parameterCapacity = baseParameters.Count + _inputModel.Properties.Count;
-            var parameterNames = baseParameters.Select(p => p.Name).ToHashSet();
-            var constructorParameters = new List<ParameterProvider>(parameterCapacity);
-
-            // add the base parameters
-            constructorParameters.AddRange(baseParameters);
-
-            // construct the initializer using the parameters from base signature
-            var constructorInitializer = new ConstructorInitializer(true, baseParameters);
-
-            foreach (var property in _model.Properties)
-            {
-                // skip those non-spec properties
-                if (property.WireInfo == null)
-                {
-                    continue;
-                }
-                constructorParameters.Add(property.AsParameter);
-            }
-
-            // Append the raw data field if it doesn't already exist in the constructor parameters
-            if (_rawDataField != null)
-            {
-                constructorParameters.Add(_rawDataField.AsParameter);
-            }
-
-            return (constructorParameters, constructorInitializer);
-        }
-
         private ConstructorProvider BuildEmptyConstructor()
         {
             var accessibility = _isStruct ? MethodSignatureModifiers.Public : MethodSignatureModifiers.Internal;
diff --git a/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/src/ScmTypeFactory.cs b/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/src/ScmTypeFactory.cs
index 65b5ed3fa84..48c0cbed76f 100644
--- a/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/src/ScmTypeFactory.cs
+++ b/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/src/ScmTypeFactory.cs
@@ -32,7 +32,11 @@ protected override IReadOnlyList<TypeProvider> CreateSerializationsCore(InputTyp
             switch (inputType)
             {
                 case InputModelType inputModel when inputModel.Usage.HasFlag(InputModelTypeUsage.Json):
-                    return [new MrwSerializationTypeDefinition(inputModel, typeProvider)];
+                    if (typeProvider is ModelProvider modelProvider)
+                    {
+                        return [new MrwSerializationTypeDefinition(inputModel, modelProvider)];
+                    }
+                    return [];
                 case InputEnumType { IsExtensible: true } inputEnumType:
                     if (ClientModelPlugin.Instance.TypeFactory.CreateCSharpType(inputEnumType)?.UnderlyingEnumType.Equals(typeof(string)) == true)
                     {
diff --git a/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/test/Providers/MrwSerializationTypeDefinitions/JsonModelCoreTests.cs b/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/test/Providers/MrwSerializationTypeDefinitions/JsonModelCoreTests.cs
index 059503adf90..2cd534cbe9a 100644
--- a/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/test/Providers/MrwSerializationTypeDefinitions/JsonModelCoreTests.cs
+++ b/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/test/Providers/MrwSerializationTypeDefinitions/JsonModelCoreTests.cs
@@ -16,13 +16,13 @@ public class JsonModelCoreTests
         public JsonModelCoreTests()
         {
             MockHelpers.LoadMockPlugin(createSerializationsCore: (inputType, typeProvider)
-                => inputType is InputModelType modeltype ? [new MockMrwProvider(modeltype, typeProvider)] : []);
+                => inputType is InputModelType modeltype ? [new MockMrwProvider(modeltype, (typeProvider as ModelProvider)!)] : []);
         }
 
         private class MockMrwProvider : MrwSerializationTypeDefinition
         {
-            public MockMrwProvider(InputModelType inputModel, TypeProvider typeProvider)
-                : base(inputModel, typeProvider)
+            public MockMrwProvider(InputModelType inputModel, ModelProvider modelProvider)
+                : base(inputModel, modelProvider)
             {
             }
 
diff --git a/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/test/Providers/MrwSerializationTypeDefinitions/MrwSerializationConstructorTests.cs b/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/test/Providers/MrwSerializationTypeDefinitions/MrwSerializationConstructorTests.cs
deleted file mode 100644
index 0fefcd0ed6f..00000000000
--- a/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/test/Providers/MrwSerializationTypeDefinitions/MrwSerializationConstructorTests.cs
+++ /dev/null
@@ -1,84 +0,0 @@
-// Copyright (c) Microsoft Corporation. All rights reserved.
-// Licensed under the MIT License.
-
-using System;
-using System.Collections.Generic;
-using Microsoft.Generator.CSharp.ClientModel.Providers;
-using Microsoft.Generator.CSharp.Input;
-using Microsoft.Generator.CSharp.Primitives;
-using Microsoft.Generator.CSharp.Providers;
-using NUnit.Framework;
-
-namespace Microsoft.Generator.CSharp.ClientModel.Tests.Providers.MrwSerializationTypeDefinitions
-{
-    public class MrwSerializationConstructorTests
-    {
-        public MrwSerializationConstructorTests()
-        {
-            MockHelpers.LoadMockPlugin(createSerializationsCore: (inputType, typeProvider)
-                => inputType is InputModelType modeltype ? [new MockMrwProvider(modeltype, typeProvider)] : []);
-        }
-
-        private class MockMrwProvider : MrwSerializationTypeDefinition
-        {
-            public MockMrwProvider(InputModelType inputModel, TypeProvider typeProvider)
-                : base(inputModel, typeProvider)
-            {
-            }
-
-            protected override MethodProvider[] BuildMethods() => [];
-
-            protected override FieldProvider[] BuildFields() => [];
-        }
-
-        [Test]
-        public void TestBuildConstructors()
-        {
-            var baseProperties = new List<InputModelProperty>
-            {
-                new InputModelProperty("prop1", "prop1", string.Empty, InputPrimitiveType.String, true, false, false),
-                new InputModelProperty("prop2", "prop2", string.Empty, InputPrimitiveType.String, false, false, false),
-            };
-            var derivedProperties = new List<InputModelProperty>
-            {
-                new InputModelProperty("prop3", "prop3", string.Empty, InputPrimitiveType.String, true, false, false),
-                new InputModelProperty("prop4", "prop4", string.Empty, InputPrimitiveType.String, false, false, false),
-            };
-            var inputBase = new InputModelType("baseModel", "baseModel", null, null, null, InputModelTypeUsage.Input, baseProperties, null, new List<InputModelType>(), null, null, new Dictionary<string, InputModelType>(), null, false);
-            var inputDerived = new InputModelType("derivedModel", "derivedModel", null, null, null, InputModelTypeUsage.Input, derivedProperties, inputBase, new List<InputModelType>(), null, null, new Dictionary<string, InputModelType>(), null, false);
-            ((List<InputModelType>)inputBase.DerivedModels).Add(inputDerived);
-
-            var (baseModel, baseSerialization) = MrwSerializationTypeDefinitionTests.CreateModelAndSerialization(inputBase);
-            var (derivedModel, derivedSerialization) = MrwSerializationTypeDefinitionTests.CreateModelAndSerialization(inputDerived);
-
-            var baseCtors = baseSerialization.Constructors;
-            var derivedCtors = derivedSerialization.Constructors;
-            Assert.AreEqual(2, baseCtors.Count);
-            Assert.AreEqual(2, derivedCtors.Count);
-            // the second ctor of the ctors should be parameterless
-            Assert.AreEqual(0, baseCtors[1].Signature.Parameters.Count);
-            Assert.AreEqual(0, derivedCtors[1].Signature.Parameters.Count);
-            // the first ctor should contain certain number of parameters
-            var baseParameters = baseCtors[0].Signature.Parameters;
-            var derivedParameters = derivedCtors[0].Signature.Parameters;
-            Assert.AreEqual(3, baseParameters.Count); // 2 properties + raw data
-            Assert.AreEqual(5, derivedParameters.Count); // 4 properties + raw data
-            Assert.AreEqual("prop1", baseParameters[0].Name);
-            Assert.AreEqual(new CSharpType(typeof(string)), baseParameters[0].Type);
-            Assert.AreEqual("prop2", baseParameters[1].Name);
-            Assert.AreEqual(new CSharpType(typeof(string), true), baseParameters[1].Type);
-            Assert.AreEqual("serializedAdditionalRawData", baseParameters[2].Name);
-            Assert.AreEqual(new CSharpType(typeof(IDictionary<string, BinaryData>)), baseParameters[2].Type);
-            Assert.AreEqual("prop1", baseParameters[0].Name);
-            Assert.AreEqual(new CSharpType(typeof(string)), derivedParameters[0].Type);
-            Assert.AreEqual("prop2", baseParameters[1].Name);
-            Assert.AreEqual(new CSharpType(typeof(string), true), derivedParameters[1].Type);
-            Assert.AreEqual("serializedAdditionalRawData", derivedParameters[2].Name);
-            Assert.AreEqual(new CSharpType(typeof(IDictionary<string, BinaryData>)), derivedParameters[2].Type);
-            Assert.AreEqual("prop3", derivedParameters[3].Name);
-            Assert.AreEqual(new CSharpType(typeof(string)), derivedParameters[3].Type);
-            Assert.AreEqual("prop4", derivedParameters[4].Name);
-            Assert.AreEqual(new CSharpType(typeof(string), true), derivedParameters[4].Type);
-        }
-    }
-}
diff --git a/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/test/Providers/MrwSerializationTypeDefinitions/MrwSerializationTypeDefinitionTests.cs b/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/test/Providers/MrwSerializationTypeDefinitions/MrwSerializationTypeDefinitionTests.cs
index 759151f6167..0ffd7305f24 100644
--- a/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/test/Providers/MrwSerializationTypeDefinitions/MrwSerializationTypeDefinitionTests.cs
+++ b/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/test/Providers/MrwSerializationTypeDefinitions/MrwSerializationTypeDefinitionTests.cs
@@ -22,10 +22,10 @@ internal class MrwSerializationTypeDefinitionTests
         public MrwSerializationTypeDefinitionTests()
         {
             MockHelpers.LoadMockPlugin(createSerializationsCore: (inputType, typeProvider) =>
-                inputType is InputModelType modelType ? [new MrwSerializationTypeDefinition(modelType, typeProvider)] : []);
+                inputType is InputModelType modelType ? [new MrwSerializationTypeDefinition(modelType, (typeProvider as ModelProvider)!)] : []);
         }
 
-        internal static (TypeProvider Model, MrwSerializationTypeDefinition Serialization) CreateModelAndSerialization(InputModelType inputModel)
+        internal static (ModelProvider Model, MrwSerializationTypeDefinition Serialization) CreateModelAndSerialization(InputModelType inputModel)
         {
             var model = ClientModelPlugin.Instance.TypeFactory.CreateModel(inputModel);
             var serializations = model!.SerializationProviders;
@@ -33,7 +33,7 @@ internal static (TypeProvider Model, MrwSerializationTypeDefinition Serializatio
             Assert.AreEqual(1, serializations.Count);
             Assert.IsInstanceOf<MrwSerializationTypeDefinition>(serializations[0]);
 
-            return (model, (MrwSerializationTypeDefinition)serializations[0]);
+            return ((model as ModelProvider)!, (MrwSerializationTypeDefinition)serializations[0]);
         }
 
         [Test]
@@ -471,37 +471,15 @@ public void TestBuildPersistableModelGetFormatMethodObjectDeclaration()
             Assert.AreEqual(1, bodyExpression?.Arguments.Count);
         }
 
-        [Test]
-        public void TestBuildSerializationConstructor()
-        {
-            var inputModel = new InputModelType("mockInputModel", "mockNamespace", "public", null, null, InputModelTypeUsage.Input | InputModelTypeUsage.Output, Array.Empty<InputModelProperty>(), null, new List<InputModelType>(), null, null, new Dictionary<string, InputModelType>(), null, false);
-            var (model, serialization) = CreateModelAndSerialization(inputModel);
-            var constructor = serialization.BuildSerializationConstructor();
-
-            Assert.IsNotNull(constructor);
-            var constructorSignature = constructor?.Signature;
-            Assert.IsNotNull(constructorSignature);
-            Assert.AreEqual(1, constructorSignature?.Parameters.Count);
-
-            var param = constructorSignature?.Parameters[0];
-            Assert.IsNotNull(param);
-            Assert.AreEqual("serializedAdditionalRawData", param?.Name);
-        }
-
         [Test]
         public void TestBuildFields()
         {
             var inputModel = new InputModelType("mockInputModel", "mockNamespace", "public", null, null, InputModelTypeUsage.Input | InputModelTypeUsage.Output, Array.Empty<InputModelProperty>(), null, new List<InputModelType>(), null, null, new Dictionary<string, InputModelType>(), null, false);
-            var (model, serialization) = CreateModelAndSerialization(inputModel);
+            var (_, serialization) = CreateModelAndSerialization(inputModel);
             var fields = serialization.Fields;
 
-            // Assert
             Assert.IsNotNull(fields);
-            Assert.AreEqual(1, fields.Count);
-            Assert.AreEqual("_serializedAdditionalRawData", fields[0].Name);
-
-            var type = fields[0].Type;
-            Assert.IsTrue(type.IsCollection);
+            Assert.AreEqual(0, fields.Count);
         }
 
         [Test]
@@ -517,17 +495,13 @@ public void TestBuildConstructor_ValidateConstructors()
 
             var inputModel = new InputModelType("TestModel", "TestModel", "public", null, "Test model.", InputModelTypeUsage.Input | InputModelTypeUsage.Output, properties, null, Array.Empty<InputModelType>(), null, null, new Dictionary<string, InputModelType>(), null, false);
 
-            var (model, serialization) = CreateModelAndSerialization(inputModel);
+            var (_, serialization) = CreateModelAndSerialization(inputModel);
             var ctors = serialization.Constructors;
             Assert.IsNotNull(ctors);
 
-            Assert.AreEqual(2, ctors.Count);
-
-            var serializationCtor = ctors[0];
-            Assert.AreEqual(MethodSignatureModifiers.Internal, serializationCtor.Signature.Modifiers);
-            Assert.AreEqual(5, serializationCtor.Signature.Parameters.Count);
+            Assert.AreEqual(1, ctors.Count);
 
-            var emptyCtor = ctors[1];
+            var emptyCtor = ctors[0];
             Assert.AreEqual(MethodSignatureModifiers.Internal, emptyCtor.Signature.Modifiers);
             Assert.AreEqual(0, emptyCtor.Signature.Parameters.Count);
         }
diff --git a/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/test/Providers/MrwSerializationTypeDefinitions/PersistableModelCoreTests.cs b/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/test/Providers/MrwSerializationTypeDefinitions/PersistableModelCoreTests.cs
index 9f5464b422a..7f95019d948 100644
--- a/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/test/Providers/MrwSerializationTypeDefinitions/PersistableModelCoreTests.cs
+++ b/packages/http-client-csharp/generator/Microsoft.Generator.CSharp.ClientModel/test/Providers/MrwSerializationTypeDefinitions/PersistableModelCoreTests.cs
@@ -16,13 +16,13 @@ public class PersistableModelCoreTests
         public PersistableModelCoreTests()
         {
             MockHelpers.LoadMockPlugin(createSerializationsCore: (inputType, typeProvider)
-                => inputType is InputModelType modeltype ? [new MockMrwProvider(modeltype, typeProvider)] : []);
+                => inputType is InputModelType modeltype ? [new MockMrwProvider(modeltype, (typeProvider as ModelProvider)!)] : []);
         }
 
         private class MockMrwProvider : MrwSerializationTypeDefinition
         {
-            public MockMrwProvider(InputModelType inputModel, TypeProvider typeProvider)
-                : base(inputModel, typeProvider)
+            public MockMrwProvider(InputModelType inputModel, ModelProvider modelProvider)
+                : base(inputModel, modelProvider)
             {
             }
 
diff --git a/packages/http-client-csharp/generator/Microsoft.Generator.CSharp/src/Providers/ModelFactoryProvider.cs b/packages/http-client-csharp/generator/Microsoft.Generator.CSharp/src/Providers/ModelFactoryProvider.cs
index 8fff3afcd54..d0a98fd7edf 100644
--- a/packages/http-client-csharp/generator/Microsoft.Generator.CSharp/src/Providers/ModelFactoryProvider.cs
+++ b/packages/http-client-csharp/generator/Microsoft.Generator.CSharp/src/Providers/ModelFactoryProvider.cs
@@ -17,6 +17,7 @@ namespace Microsoft.Generator.CSharp.Providers
     internal class ModelFactoryProvider : TypeProvider
     {
         private const string ModelFactorySuffix = "ModelFactory";
+        private const string AdditionalRawDataParameterName = "serializedAdditionalRawData";
 
         private readonly IEnumerable<InputModelType> _models;
 
@@ -66,17 +67,18 @@ protected override MethodProvider[] BuildMethods()
             var methods = new List<MethodProvider>(_models.Count());
             foreach (var model in _models)
             {
-                var modelProvider = CodeModelPlugin.Instance.TypeFactory.CreateModel(model);
+                var modelProvider = CodeModelPlugin.Instance.TypeFactory.CreateModel(model) as ModelProvider;
                 if (modelProvider is null || modelProvider.DeclarationModifiers.HasFlag(TypeSignatureModifiers.Internal))
                     continue;
 
+                var modelCtor = modelProvider.FullConstructor;
                 var signature = new MethodSignature(
                     modelProvider.Name,
                     null,
                     MethodSignatureModifiers.Static | MethodSignatureModifiers.Public,
                     modelProvider.Type,
                     $"A new {modelProvider.Type:C} instance for mocking.",
-                    GetParameters(modelProvider));
+                    GetParameters(modelCtor));
 
                 var docs = new XmlDocProvider();
                 docs.Summary = modelProvider.XmlDocs?.Summary;
@@ -98,7 +100,7 @@ .. GetCollectionInitialization(signature),
             return [.. methods];
         }
 
-        private IReadOnlyList<ValueExpression> GetCtorParams(MethodSignature signature)
+        private static IReadOnlyList<ValueExpression> GetCtorParams(MethodSignature signature)
         {
             var expressions = new List<ValueExpression>(signature.Parameters.Count);
             foreach (var param in signature.Parameters)
@@ -112,6 +114,7 @@ private IReadOnlyList<ValueExpression> GetCtorParams(MethodSignature signature)
                     expressions.Add(param);
                 }
             }
+
             expressions.Add(Null);
             return [.. expressions];
         }
@@ -133,20 +136,21 @@ private IReadOnlyList<MethodBodyStatement> GetCollectionInitialization(MethodSig
             return [.. statements];
         }
 
-        private IReadOnlyList<ParameterProvider> GetParameters(TypeProvider modelProvider)
+        private static IReadOnlyList<ParameterProvider> GetParameters(ConstructorProvider modelFullConstructor)
         {
-            var parameters = new List<ParameterProvider>(modelProvider.Properties.Count);
-            foreach (var property in modelProvider.Properties)
+            var modelCtorParams = modelFullConstructor.Signature.Parameters;
+            var parameters = new List<ParameterProvider>(modelCtorParams.Count);
+            foreach (var param in modelCtorParams)
             {
-                if (property.Modifiers.HasFlag(MethodSignatureModifiers.Internal))
+                if (param.Name.Equals(AdditionalRawDataParameterName))
                     continue;
 
-                parameters.Add(GetModelFactoryParam(property.AsParameter));
+                parameters.Add(GetModelFactoryParam(param));
             }
             return [.. parameters];
         }
 
-        private ParameterProvider GetModelFactoryParam(ParameterProvider parameter)
+        private static ParameterProvider GetModelFactoryParam(ParameterProvider parameter)
         {
             return new ParameterProvider(
                 parameter.Name,
diff --git a/packages/http-client-csharp/generator/Microsoft.Generator.CSharp/src/Providers/ModelProvider.cs b/packages/http-client-csharp/generator/Microsoft.Generator.CSharp/src/Providers/ModelProvider.cs
index 88591d9c2a9..9a9c6fbb08b 100644
--- a/packages/http-client-csharp/generator/Microsoft.Generator.CSharp/src/Providers/ModelProvider.cs
+++ b/packages/http-client-csharp/generator/Microsoft.Generator.CSharp/src/Providers/ModelProvider.cs
@@ -16,12 +16,19 @@ namespace Microsoft.Generator.CSharp.Providers
 {
     public sealed class ModelProvider : TypeProvider
     {
+        private const string PrivateAdditionalPropertiesPropertyDescription = "Keeps track of any properties unknown to the library.";
+        private const string PrivateAdditionalPropertiesPropertyName = "_serializedAdditionalRawData";
         private readonly InputModelType _inputModel;
 
         protected override FormattableString Description { get; }
 
         private readonly bool _isStruct;
         private readonly TypeSignatureModifiers _declarationModifiers;
+        private readonly CSharpType _privateAdditionalRawDataPropertyType = typeof(IDictionary<string, BinaryData>);
+        private readonly Lazy<TypeProvider?>? _baseTypeProvider;
+        private FieldProvider? _rawDataField;
+        private ModelProvider? _baseModelProvider;
+        private ConstructorProvider? _fullConstructor;
 
         public ModelProvider(InputModelType inputModel)
         {
@@ -29,6 +36,7 @@ public ModelProvider(InputModelType inputModel)
             Description = inputModel.Description != null ? FormattableStringHelpers.FromString(inputModel.Description) : $"The {Name}.";
             _declarationModifiers = TypeSignatureModifiers.Partial |
                 (inputModel.ModelAsStruct ? TypeSignatureModifiers.ReadOnly | TypeSignatureModifiers.Struct : TypeSignatureModifiers.Class);
+
             if (inputModel.Access == "internal")
             {
                 _declarationModifiers |= TypeSignatureModifiers.Internal;
@@ -40,17 +48,25 @@ public ModelProvider(InputModelType inputModel)
                 _declarationModifiers |= TypeSignatureModifiers.Abstract;
             }
 
+            if (inputModel.BaseModel is not null)
+            {
+                _baseTypeProvider = new(() => CodeModelPlugin.Instance.TypeFactory.CreateModel(inputModel.BaseModel));
+            }
+
             _isStruct = inputModel.ModelAsStruct;
         }
 
+        private ModelProvider? BaseModelProvider
+            => _baseModelProvider ??= (_baseTypeProvider?.Value is ModelProvider baseModelProvider ? baseModelProvider : null);
+        private FieldProvider? RawDataField => _rawDataField ??= BuildRawDataField();
+
+        public ConstructorProvider FullConstructor => _fullConstructor ??= BuildFullConstructor();
+
         protected override string GetNamespace() => CodeModelPlugin.Instance.Configuration.ModelNamespace;
 
         protected override CSharpType? GetBaseType()
         {
-            if (_inputModel.BaseModel == null)
-                return null;
-
-            return CodeModelPlugin.Instance.TypeFactory.CreateModel(_inputModel.BaseModel)?.Type;
+            return BaseModelProvider?.Type;
         }
 
         protected override TypeProvider[] BuildSerializationProviders()
@@ -64,6 +80,15 @@ protected override TypeProvider[] BuildSerializationProviders()
 
         protected override TypeSignatureModifiers GetDeclarationModifiers() => _declarationModifiers;
 
+        /// <summary>
+        /// Builds the fields for the model by adding the raw data field.
+        /// </summary>
+        /// <returns>The list of <see cref="FieldProvider"/> for the model.</returns>
+        protected override FieldProvider[] BuildFields()
+        {
+            return RawDataField != null ? [RawDataField] : [];
+        }
+
         protected override PropertyProvider[] BuildProperties()
         {
             var propertiesCount = _inputModel.Properties.Count;
@@ -86,7 +111,7 @@ protected override ConstructorProvider[] BuildConstructors()
         {
             if (_inputModel.IsUnknownDiscriminatorModel)
             {
-                return [];
+                return [FullConstructor];
             }
 
             // Build the initialization constructor
@@ -95,7 +120,7 @@ protected override ConstructorProvider[] BuildConstructors()
                 : _inputModel.Usage.HasFlag(InputModelTypeUsage.Input)
                     ? MethodSignatureModifiers.Public
                     : MethodSignatureModifiers.Internal;
-            var (constructorParameters, constructorInitializer) = BuildConstructorParameters();
+            var (constructorParameters, constructorInitializer) = BuildConstructorParameters(true);
 
             var constructor = new ConstructorProvider(
                 signature: new ConstructorSignature(
@@ -106,28 +131,64 @@ protected override ConstructorProvider[] BuildConstructors()
                     Initializer: constructorInitializer),
                 bodyStatements: new MethodBodyStatement[]
                 {
-                    GetPropertyInitializers(constructorParameters)
+                    GetPropertyInitializers(true, parameters: constructorParameters)
                 },
                 this);
 
+            if (!constructorParameters.SequenceEqual(FullConstructor.Signature.Parameters))
+            {
+                return [constructor, FullConstructor];
+            }
+
             return [constructor];
         }
 
-        // TODO -- figure out how to reuse this piece of code because similar code exists in MrwSerializationDefinition as well https://github.com/microsoft/typespec/issues/3871
-        private (IReadOnlyList<ParameterProvider> Parameters, ConstructorInitializer? Initializer) BuildConstructorParameters()
+        /// <summary>
+        /// Builds the internal constructor for the model which contains all public properties
+        /// as parameters.
+        /// </summary>
+        private ConstructorProvider BuildFullConstructor()
         {
-            // we need to find all the properties on our base model, we add the reverse because our convention is to have the properties from base model first.
-            var baseProperties = _inputModel.GetAllBaseModels().Reverse().SelectMany(model => CodeModelPlugin.Instance.TypeFactory.CreateModel(model)?.Properties ?? []);
-            var basePropertyCount = baseProperties.Count();
-            var parameterCapacity = basePropertyCount + Properties.Count;
-            var baseParameters = new List<ParameterProvider>(basePropertyCount);
-            var constructorParameters = new List<ParameterProvider>(parameterCapacity);
-
-            // add the base parameters
+            var (ctorParameters, ctorInitializer) = BuildConstructorParameters(false);
+
+            return new ConstructorProvider(
+                signature: new ConstructorSignature(
+                    Type,
+                    $"Initializes a new instance of {Type:C}",
+                    MethodSignatureModifiers.Internal,
+                    ctorParameters,
+                    Initializer: ctorInitializer),
+                bodyStatements: new MethodBodyStatement[]
+                {
+                    GetPropertyInitializers(false)
+                },
+                this);
+        }
+
+        private (IReadOnlyList<ParameterProvider> Parameters, ConstructorInitializer? Initializer) BuildConstructorParameters(
+            bool isPrimaryConstructor)
+        {
+            var baseParameters = new List<ParameterProvider>();
+            var constructorParameters = new List<ParameterProvider>();
+            IEnumerable<PropertyProvider> baseProperties = [];
+
+            if (isPrimaryConstructor)
+            {
+                baseProperties = _inputModel.GetAllBaseModels()
+                    .Reverse()
+                    .SelectMany(model => CodeModelPlugin.Instance.TypeFactory.CreateModel(model)?.Properties ?? []);
+            }
+            else if (BaseModelProvider?.FullConstructor.Signature != null)
+            {
+                baseParameters.AddRange(BaseModelProvider.FullConstructor.Signature.Parameters);
+            }
+
+            // add the base parameters, if any
             foreach (var property in baseProperties)
             {
-                AddInitializationParameter(baseParameters, property, _isStruct);
+                AddInitializationParameterForCtor(baseParameters, property, _isStruct, isPrimaryConstructor);
             }
+
             constructorParameters.AddRange(baseParameters);
 
             // construct the initializer using the parameters from base signature
@@ -135,19 +196,32 @@ protected override ConstructorProvider[] BuildConstructors()
 
             foreach (var property in Properties)
             {
-                AddInitializationParameter(constructorParameters, property, _isStruct);
+                AddInitializationParameterForCtor(constructorParameters, property, _isStruct, isPrimaryConstructor);
+            }
+
+            if (RawDataField != null && !isPrimaryConstructor)
+            {
+                constructorParameters.Add(RawDataField.AsParameter);
             }
 
             return (constructorParameters, constructorInitializer);
+        }
 
-            static void AddInitializationParameter(List<ParameterProvider> parameters, PropertyProvider property, bool isStruct)
+        private static void AddInitializationParameterForCtor(
+            List<ParameterProvider> parameters,
+            PropertyProvider property,
+            bool isStruct,
+            bool isPrimaryConstructor)
+        {
+            // We only add those properties with wire info indicating they are coming from specs.
+            if (property.WireInfo is not { } wireInfo)
             {
-                // we only add those properties with wire info indicating they are coming from specs.
-                if (property.WireInfo is not { } wireInfo)
-                {
-                    return;
-                }
-                if (isStruct || (wireInfo is { IsRequired: true, IsDiscriminator: false } && !property.Type.IsLiteral))
+                return;
+            }
+
+            if (isPrimaryConstructor)
+            {
+                if (isStruct || (wireInfo.IsRequired && !wireInfo.IsDiscriminator && !property.Type.IsLiteral))
                 {
                     if (!wireInfo.IsReadOnly)
                     {
@@ -155,18 +229,35 @@ static void AddInitializationParameter(List<ParameterProvider> parameters, Prope
                     }
                 }
             }
+            else
+            {
+                // For the serialization constructor, we always add the property as a parameter
+                parameters.Add(property.AsParameter);
+            }
         }
 
-        private MethodBodyStatement GetPropertyInitializers(IReadOnlyList<ParameterProvider> parameters)
+        private MethodBodyStatement GetPropertyInitializers(
+            bool isPrimaryConstructor,
+            IReadOnlyList<ParameterProvider>? parameters = null)
         {
-            List<MethodBodyStatement> methodBodyStatements = new();
-
-            Dictionary<string, ParameterProvider> parameterMap = parameters.ToDictionary(
-                parameter => parameter.Name,
-                parameter => parameter);
+            List<MethodBodyStatement> methodBodyStatements = new(Properties.Count + 1);
+            Dictionary<string, ParameterProvider> parameterMap = parameters?.ToDictionary(p => p.Name) ?? [];
 
             foreach (var property in Properties)
             {
+                // skip those non-spec properties
+                if (property.WireInfo == null)
+                {
+                    continue;
+                }
+
+                if (!isPrimaryConstructor)
+                {
+                    // always add the property for the serialization constructor
+                    methodBodyStatements.Add(property.Assign(property.AsParameter).Terminate());
+                    continue;
+                }
+
                 ValueExpression? initializationValue = null;
 
                 if (parameterMap.TryGetValue(property.AsParameter.Name, out var parameter) || _isStruct)
@@ -194,7 +285,39 @@ private MethodBodyStatement GetPropertyInitializers(IReadOnlyList<ParameterProvi
                 }
             }
 
+            if (!isPrimaryConstructor && RawDataField != null)
+            {
+                methodBodyStatements.Add(RawDataField.Assign(RawDataField.AsParameter).Terminate());
+            }
+
             return methodBodyStatements;
         }
+
+        /// <summary>
+        /// Builds the raw data field for the model to be used for serialization.
+        /// </summary>
+        /// <returns>The constructed <see cref="FieldProvider"/> if the model should generate the field.</returns>
+        private FieldProvider? BuildRawDataField()
+        {
+            // check if there is a raw data field on my base, if so, we do not have to have one here
+            if (BaseModelProvider?.RawDataField != null)
+            {
+                return null;
+            }
+
+            var modifiers = FieldModifiers.Private;
+            if (!DeclarationModifiers.HasFlag(TypeSignatureModifiers.Sealed))
+            {
+                modifiers |= FieldModifiers.Protected;
+            }
+
+            var rawDataField = new FieldProvider(
+                modifiers: modifiers,
+                type: _privateAdditionalRawDataPropertyType,
+                description: FormattableStringHelpers.FromString(PrivateAdditionalPropertiesPropertyDescription),
+                name: PrivateAdditionalPropertiesPropertyName);
+
+            return rawDataField;
+        }
     }
 }
diff --git a/packages/http-client-csharp/generator/Microsoft.Generator.CSharp/test/Providers/ModelProviderTests.cs b/packages/http-client-csharp/generator/Microsoft.Generator.CSharp/test/Providers/ModelProviderTests.cs
index 9be72c0d4b5..4384435efc7 100644
--- a/packages/http-client-csharp/generator/Microsoft.Generator.CSharp/test/Providers/ModelProviderTests.cs
+++ b/packages/http-client-csharp/generator/Microsoft.Generator.CSharp/test/Providers/ModelProviderTests.cs
@@ -102,7 +102,7 @@ public static IEnumerable<TestCaseData> BuildProperties_ValidatePropertySettersT
         };
 
         [Test]
-        public void BuildConstructor_ValidateConstructors()
+        public void TestBuildConstructor_ValidateConstructors()
         {
             var properties = new List<InputModelProperty>{
                     new InputModelProperty("requiredString", "requiredString", "", InputPrimitiveType.String, true, false, false),
@@ -132,15 +132,20 @@ public void BuildConstructor_ValidateConstructors()
             var ctors = modelTypeProvider.Constructors;
             Assert.IsNotNull(ctors);
 
-            Assert.AreEqual(1, ctors.Count);
+            Assert.AreEqual(2, ctors.Count);
 
-            var initializationCtor = ctors[0];
-            Assert.AreEqual(MethodSignatureModifiers.Public, initializationCtor.Signature.Modifiers);
+            var initializationCtor = ctors.FirstOrDefault(c => c.Signature.Modifiers.HasFlag(MethodSignatureModifiers.Public));
+            Assert.IsNotNull(initializationCtor);
+            Assert.AreEqual(MethodSignatureModifiers.Public, initializationCtor!.Signature.Modifiers);
             Assert.AreEqual(3, initializationCtor.Signature.Parameters.Count);
+
+            var secondaryCtor = ctors.FirstOrDefault(c => c.Signature.Modifiers.HasFlag(MethodSignatureModifiers.Internal));
+            Assert.IsNotNull(secondaryCtor);
+            Assert.AreEqual(6, secondaryCtor!.Signature.Parameters.Count);
         }
 
         [Test]
-        public void BuildConstructor_ValidateConstructorsInDerivedModel()
+        public void TestBuildConstructor_ValidateConstructorsInDerivedModel()
         {
             var baseProperties = new List<InputModelProperty>
             {
@@ -163,15 +168,18 @@ public void BuildConstructor_ValidateConstructorsInDerivedModel()
 
             Assert.NotNull(baseModel);
             var baseCtors = baseModel!.Constructors;
-            Assert.AreEqual(1, baseCtors.Count);
+            Assert.AreEqual(2, baseCtors.Count);
             Assert.NotNull(derivedModel);
             var derivedCtors = derivedModel!.Constructors;
-            Assert.AreEqual(1, derivedCtors.Count);
+            Assert.AreEqual(2, derivedCtors.Count);
+
+            var baseCtor = baseCtors.FirstOrDefault(c => c.Signature.Modifiers.HasFlag(MethodSignatureModifiers.Public));
+            var derivedCtor = derivedCtors.FirstOrDefault(c => c.Signature.Modifiers.HasFlag(MethodSignatureModifiers.Public));
+            Assert.NotNull(baseCtor);
+            Assert.NotNull(derivedCtor);
 
-            var baseCtor = baseCtors[0];
-            var derivedCtor = derivedCtors[0];
-            var baseParameters = baseCtor.Signature.Parameters;
-            var derivedParameters = derivedCtor.Signature.Parameters;
+            var baseParameters = baseCtor!.Signature.Parameters;
+            var derivedParameters = derivedCtor!.Signature.Parameters;
             Assert.AreEqual(1, baseParameters.Count);
             Assert.AreEqual("prop1", baseParameters[0].Name);
             Assert.AreEqual(new CSharpType(typeof(string)), baseParameters[0].Type);
@@ -180,6 +188,53 @@ public void BuildConstructor_ValidateConstructorsInDerivedModel()
             Assert.AreEqual(new CSharpType(typeof(string)), derivedParameters[0].Type);
             Assert.AreEqual("prop3", derivedParameters[1].Name);
             Assert.AreEqual(new CSharpType(typeof(string)), derivedParameters[1].Type);
+
+            // validate the secondary constructor
+            var secondaryCtor = baseCtors.FirstOrDefault(c => c.Signature.Modifiers.HasFlag(MethodSignatureModifiers.Internal));
+            var derivedSecondaryCtor = derivedCtors.FirstOrDefault(c => c.Signature.Modifiers.HasFlag(MethodSignatureModifiers.Internal));
+            Assert.NotNull(secondaryCtor);
+            Assert.NotNull(derivedSecondaryCtor);
+
+            var secondaryCtorParameters = secondaryCtor!.Signature.Parameters;
+            var derivedSecondaryCtorParams = derivedSecondaryCtor!.Signature.Parameters;
+
+            // validate secondary constructor
+            Assert.AreEqual(3, secondaryCtorParameters.Count); // 2 properties + 1 additionalRawData
+            Assert.AreEqual("prop1", secondaryCtorParameters[0].Name);
+            Assert.AreEqual(new CSharpType(typeof(string)), secondaryCtorParameters[0].Type);
+            Assert.AreEqual("prop2", secondaryCtorParameters[1].Name);
+            Assert.AreEqual(new CSharpType(typeof(string), true), secondaryCtorParameters[1].Type);
+            Assert.AreEqual("serializedAdditionalRawData", secondaryCtorParameters[2].Name);
+            Assert.AreEqual(new CSharpType(typeof(IDictionary<string, BinaryData>)), secondaryCtorParameters[2].Type);
+            // validate derived secondary constructor
+            Assert.AreEqual(5, derivedSecondaryCtorParams.Count); // all base props + 2 properties + 1 additionalRawData
+            Assert.AreEqual("prop1", derivedSecondaryCtorParams[0].Name);
+            Assert.AreEqual(new CSharpType(typeof(string)), derivedSecondaryCtorParams[0].Type);
+            Assert.AreEqual("prop2", derivedSecondaryCtorParams[1].Name);
+            Assert.AreEqual(new CSharpType(typeof(string), true), derivedSecondaryCtorParams[1].Type);
+            Assert.AreEqual("serializedAdditionalRawData", derivedSecondaryCtorParams[2].Name);
+            Assert.AreEqual(new CSharpType(typeof(IDictionary<string, BinaryData>)), derivedSecondaryCtorParams[2].Type);
+            Assert.AreEqual("prop3", derivedSecondaryCtorParams[3].Name);
+            Assert.AreEqual(new CSharpType(typeof(string)), derivedSecondaryCtorParams[3].Type);
+            Assert.AreEqual("prop4", derivedSecondaryCtorParams[4].Name);
+            Assert.AreEqual(new CSharpType(typeof(string), true), derivedSecondaryCtorParams[4].Type);
+        }
+
+        [Test]
+        public void TestBuildSecondaryConstructor()
+        {
+            var inputModel = new InputModelType("TestModel", "TestModel", "public", null, "Test model.", InputModelTypeUsage.Input | InputModelTypeUsage.Output, [], null, Array.Empty<InputModelType>(), null, null, new Dictionary<string, InputModelType>(), null, false);
+            var modelTypeProvider = new ModelProvider(inputModel);
+            var secondaryConstructor = modelTypeProvider.Constructors.FirstOrDefault(c => c.Signature.Modifiers.HasFlag(MethodSignatureModifiers.Internal));
+
+            Assert.IsNotNull(secondaryConstructor);
+            var constructorSignature = secondaryConstructor?.Signature;
+            Assert.IsNotNull(constructorSignature);
+            Assert.AreEqual(1, constructorSignature?.Parameters.Count);
+
+            var param = constructorSignature?.Parameters[0];
+            Assert.IsNotNull(param);
+            Assert.AreEqual("serializedAdditionalRawData", param?.Name);
         }
 
         [Test]
@@ -225,5 +280,21 @@ public void BuildModelAsStruct()
             var modelTypeProvider = new ModelProvider(inputModel);
             Assert.AreEqual(TypeSignatureModifiers.Public | TypeSignatureModifiers.Struct | TypeSignatureModifiers.Partial | TypeSignatureModifiers.ReadOnly, modelTypeProvider.DeclarationModifiers);
         }
+
+        [Test]
+        public void TestBuildFields()
+        {
+            var inputModel = new InputModelType("TestModel", "TestModel", "public", null, "Test model.", InputModelTypeUsage.Input | InputModelTypeUsage.Output, [], null, Array.Empty<InputModelType>(), null, null, new Dictionary<string, InputModelType>(), null, false);
+            var modelTypeProvider = new ModelProvider(inputModel);
+            var fields = modelTypeProvider.Fields;
+
+            // Assert
+            Assert.IsNotNull(fields);
+            Assert.AreEqual(1, fields.Count);
+            Assert.AreEqual("_serializedAdditionalRawData", fields[0].Name);
+
+            var type = fields[0].Type;
+            Assert.IsTrue(type.IsCollection);
+        }
     }
 }
diff --git a/packages/http-client-csharp/generator/Microsoft.Generator.CSharp/test/Writers/TestData/TypeProviderWriterTests/TypeProviderWriter_WriteModel.cs b/packages/http-client-csharp/generator/Microsoft.Generator.CSharp/test/Writers/TestData/TypeProviderWriterTests/TypeProviderWriter_WriteModel.cs
index 135ea17a8e7..d73f1b3e763 100644
--- a/packages/http-client-csharp/generator/Microsoft.Generator.CSharp/test/Writers/TestData/TypeProviderWriterTests/TypeProviderWriter_WriteModel.cs
+++ b/packages/http-client-csharp/generator/Microsoft.Generator.CSharp/test/Writers/TestData/TypeProviderWriterTests/TypeProviderWriter_WriteModel.cs
@@ -3,6 +3,7 @@
 #nullable disable
 
 using System;
+using System.Collections.Generic;
 using Sample;
 
 namespace Sample.Models
@@ -10,6 +11,9 @@ namespace Sample.Models
     /// <summary> Test model. </summary>
     public partial class TestModel
     {
+        /// <summary> Keeps track of any properties unknown to the library. </summary>
+        private global::System.Collections.Generic.IDictionary<string, global::System.BinaryData> _serializedAdditionalRawData;
+
         /// <summary> Initializes a new instance of <see cref="global::Sample.Models.TestModel"/>. </summary>
         /// <param name="requiredString"> Required string, illustrating a reference type property. </param>
         /// <param name="requiredInt"> Required int, illustrating a value type property. </param>
@@ -22,6 +26,13 @@ public TestModel(string requiredString, int requiredInt)
             RequiredInt = requiredInt;
         }
 
+        internal TestModel(string requiredString, int requiredInt, global::System.Collections.Generic.IDictionary<string, global::System.BinaryData> serializedAdditionalRawData)
+        {
+            RequiredString = requiredString;
+            RequiredInt = requiredInt;
+            _serializedAdditionalRawData = serializedAdditionalRawData;
+        }
+
         /// <summary> Required string, illustrating a reference type property. </summary>
         public string RequiredString { get; set; }
 
diff --git a/packages/http-client-csharp/generator/Microsoft.Generator.CSharp/test/Writers/TestData/TypeProviderWriterTests/TypeProviderWriter_WriteModelAsStruct.cs b/packages/http-client-csharp/generator/Microsoft.Generator.CSharp/test/Writers/TestData/TypeProviderWriterTests/TypeProviderWriter_WriteModelAsStruct.cs
index cefc259e49e..5947efd6e6e 100644
--- a/packages/http-client-csharp/generator/Microsoft.Generator.CSharp/test/Writers/TestData/TypeProviderWriterTests/TypeProviderWriter_WriteModelAsStruct.cs
+++ b/packages/http-client-csharp/generator/Microsoft.Generator.CSharp/test/Writers/TestData/TypeProviderWriterTests/TypeProviderWriter_WriteModelAsStruct.cs
@@ -3,6 +3,7 @@
 #nullable disable
 
 using System;
+using System.Collections.Generic;
 using Sample;
 
 namespace Sample.Models
@@ -10,6 +11,9 @@ namespace Sample.Models
     /// <summary> Test model. </summary>
     public readonly partial struct TestModel
     {
+        /// <summary> Keeps track of any properties unknown to the library. </summary>
+        private global::System.Collections.Generic.IDictionary<string, global::System.BinaryData> _serializedAdditionalRawData;
+
         /// <summary> Initializes a new instance of <see cref="global::Sample.Models.TestModel"/>. </summary>
         /// <param name="requiredString"> Required string, illustrating a reference type property. </param>
         /// <param name="requiredInt"> Required int, illustrating a value type property. </param>
@@ -22,6 +26,13 @@ public TestModel(string requiredString, int requiredInt)
             RequiredInt = requiredInt;
         }
 
+        internal TestModel(string requiredString, int requiredInt, global::System.Collections.Generic.IDictionary<string, global::System.BinaryData> serializedAdditionalRawData)
+        {
+            RequiredString = requiredString;
+            RequiredInt = requiredInt;
+            _serializedAdditionalRawData = serializedAdditionalRawData;
+        }
+
         /// <summary> Required string, illustrating a reference type property. </summary>
         public string RequiredString { get; set; }
 
diff --git a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/AnonymousBodyRequest.Serialization.cs b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/AnonymousBodyRequest.Serialization.cs
index e8f5bf92130..ae451492ff2 100644
--- a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/AnonymousBodyRequest.Serialization.cs
+++ b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/AnonymousBodyRequest.Serialization.cs
@@ -14,27 +14,6 @@ namespace UnbrandedTypeSpec.Models
     /// <summary></summary>
     public partial class AnonymousBodyRequest : IJsonModel<AnonymousBodyRequest>
     {
-        /// <summary> Keeps track of any properties unknown to the library. </summary>
-        private IDictionary<string, BinaryData> _serializedAdditionalRawData;
-
-        internal AnonymousBodyRequest(string name, BinaryData requiredUnion, AnonymousBodyRequestRequiredLiteralString requiredLiteralString, AnonymousBodyRequestRequiredLiteralInt requiredLiteralInt, AnonymousBodyRequestRequiredLiteralFloat requiredLiteralFloat, bool requiredLiteralBool, AnonymousBodyRequestOptionalLiteralString? optionalLiteralString, AnonymousBodyRequestOptionalLiteralInt? optionalLiteralInt, AnonymousBodyRequestOptionalLiteralFloat? optionalLiteralFloat, bool? optionalLiteralBool, string requiredBadDescription, IList<int> optionalNullableList, IList<int> requiredNullableList, IDictionary<string, BinaryData> serializedAdditionalRawData)
-        {
-            Name = name;
-            RequiredUnion = requiredUnion;
-            RequiredLiteralString = requiredLiteralString;
-            RequiredLiteralInt = requiredLiteralInt;
-            RequiredLiteralFloat = requiredLiteralFloat;
-            RequiredLiteralBool = requiredLiteralBool;
-            OptionalLiteralString = optionalLiteralString;
-            OptionalLiteralInt = optionalLiteralInt;
-            OptionalLiteralFloat = optionalLiteralFloat;
-            OptionalLiteralBool = optionalLiteralBool;
-            RequiredBadDescription = requiredBadDescription;
-            OptionalNullableList = optionalNullableList;
-            RequiredNullableList = requiredNullableList;
-            _serializedAdditionalRawData = serializedAdditionalRawData;
-        }
-
         internal AnonymousBodyRequest()
         {
         }
diff --git a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/AnonymousBodyRequest.cs b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/AnonymousBodyRequest.cs
index f27d4508cd4..f3990e0ab41 100644
--- a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/AnonymousBodyRequest.cs
+++ b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/AnonymousBodyRequest.cs
@@ -13,6 +13,9 @@ namespace UnbrandedTypeSpec.Models
     /// <summary> The AnonymousBodyRequest. </summary>
     public partial class AnonymousBodyRequest
     {
+        /// <summary> Keeps track of any properties unknown to the library. </summary>
+        private IDictionary<string, BinaryData> _serializedAdditionalRawData;
+
         internal AnonymousBodyRequest(string name, BinaryData requiredUnion, string requiredBadDescription, IEnumerable<int> requiredNullableList)
         {
             Name = name;
@@ -22,6 +25,24 @@ internal AnonymousBodyRequest(string name, BinaryData requiredUnion, string requ
             RequiredNullableList = requiredNullableList?.ToList();
         }
 
+        internal AnonymousBodyRequest(string name, BinaryData requiredUnion, AnonymousBodyRequestRequiredLiteralString requiredLiteralString, AnonymousBodyRequestRequiredLiteralInt requiredLiteralInt, AnonymousBodyRequestRequiredLiteralFloat requiredLiteralFloat, bool requiredLiteralBool, AnonymousBodyRequestOptionalLiteralString? optionalLiteralString, AnonymousBodyRequestOptionalLiteralInt? optionalLiteralInt, AnonymousBodyRequestOptionalLiteralFloat? optionalLiteralFloat, bool? optionalLiteralBool, string requiredBadDescription, IList<int> optionalNullableList, IList<int> requiredNullableList, IDictionary<string, BinaryData> serializedAdditionalRawData)
+        {
+            Name = name;
+            RequiredUnion = requiredUnion;
+            RequiredLiteralString = requiredLiteralString;
+            RequiredLiteralInt = requiredLiteralInt;
+            RequiredLiteralFloat = requiredLiteralFloat;
+            RequiredLiteralBool = requiredLiteralBool;
+            OptionalLiteralString = optionalLiteralString;
+            OptionalLiteralInt = optionalLiteralInt;
+            OptionalLiteralFloat = optionalLiteralFloat;
+            OptionalLiteralBool = optionalLiteralBool;
+            RequiredBadDescription = requiredBadDescription;
+            OptionalNullableList = optionalNullableList;
+            RequiredNullableList = requiredNullableList;
+            _serializedAdditionalRawData = serializedAdditionalRawData;
+        }
+
         /// <summary> name of the Thing. </summary>
         public string Name { get; set; }
 
diff --git a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/Friend.Serialization.cs b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/Friend.Serialization.cs
index aaa33a52caf..52185a7693f 100644
--- a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/Friend.Serialization.cs
+++ b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/Friend.Serialization.cs
@@ -14,15 +14,6 @@ namespace UnbrandedTypeSpec.Models
     /// <summary></summary>
     public partial class Friend : IJsonModel<Friend>
     {
-        /// <summary> Keeps track of any properties unknown to the library. </summary>
-        private IDictionary<string, BinaryData> _serializedAdditionalRawData;
-
-        internal Friend(string name, IDictionary<string, BinaryData> serializedAdditionalRawData)
-        {
-            Name = name;
-            _serializedAdditionalRawData = serializedAdditionalRawData;
-        }
-
         internal Friend()
         {
         }
diff --git a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/Friend.cs b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/Friend.cs
index c0c5278ef2f..57cf2e65c65 100644
--- a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/Friend.cs
+++ b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/Friend.cs
@@ -2,16 +2,28 @@
 
 #nullable disable
 
+using System;
+using System.Collections.Generic;
+
 namespace UnbrandedTypeSpec.Models
 {
     /// <summary> this is not a friendly model but with a friendly name. </summary>
     public partial class Friend
     {
+        /// <summary> Keeps track of any properties unknown to the library. </summary>
+        private IDictionary<string, BinaryData> _serializedAdditionalRawData;
+
         internal Friend(string name)
         {
             Name = name;
         }
 
+        internal Friend(string name, IDictionary<string, BinaryData> serializedAdditionalRawData)
+        {
+            Name = name;
+            _serializedAdditionalRawData = serializedAdditionalRawData;
+        }
+
         /// <summary> name of the NotFriend. </summary>
         public string Name { get; set; }
     }
diff --git a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/FriendlyModelRequest.Serialization.cs b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/FriendlyModelRequest.Serialization.cs
index 8d3368c78d7..bee8747b3c3 100644
--- a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/FriendlyModelRequest.Serialization.cs
+++ b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/FriendlyModelRequest.Serialization.cs
@@ -14,15 +14,6 @@ namespace UnbrandedTypeSpec.Models
     /// <summary></summary>
     public partial class FriendlyModelRequest : IJsonModel<FriendlyModelRequest>
     {
-        /// <summary> Keeps track of any properties unknown to the library. </summary>
-        private IDictionary<string, BinaryData> _serializedAdditionalRawData;
-
-        internal FriendlyModelRequest(string name, IDictionary<string, BinaryData> serializedAdditionalRawData)
-        {
-            Name = name;
-            _serializedAdditionalRawData = serializedAdditionalRawData;
-        }
-
         internal FriendlyModelRequest()
         {
         }
diff --git a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/FriendlyModelRequest.cs b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/FriendlyModelRequest.cs
index f00cb7192a5..f48ffdeca89 100644
--- a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/FriendlyModelRequest.cs
+++ b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/FriendlyModelRequest.cs
@@ -2,16 +2,28 @@
 
 #nullable disable
 
+using System;
+using System.Collections.Generic;
+
 namespace UnbrandedTypeSpec.Models
 {
     /// <summary> The FriendlyModelRequest. </summary>
     public partial class FriendlyModelRequest
     {
+        /// <summary> Keeps track of any properties unknown to the library. </summary>
+        private IDictionary<string, BinaryData> _serializedAdditionalRawData;
+
         internal FriendlyModelRequest(string name)
         {
             Name = name;
         }
 
+        internal FriendlyModelRequest(string name, IDictionary<string, BinaryData> serializedAdditionalRawData)
+        {
+            Name = name;
+            _serializedAdditionalRawData = serializedAdditionalRawData;
+        }
+
         /// <summary> name of the NotFriend. </summary>
         public string Name { get; set; }
     }
diff --git a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ModelWithRequiredNullableProperties.Serialization.cs b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ModelWithRequiredNullableProperties.Serialization.cs
index 96283583f4a..f89d12b6d7c 100644
--- a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ModelWithRequiredNullableProperties.Serialization.cs
+++ b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ModelWithRequiredNullableProperties.Serialization.cs
@@ -14,17 +14,6 @@ namespace UnbrandedTypeSpec.Models
     /// <summary></summary>
     public partial class ModelWithRequiredNullableProperties : IJsonModel<ModelWithRequiredNullableProperties>
     {
-        /// <summary> Keeps track of any properties unknown to the library. </summary>
-        private IDictionary<string, BinaryData> _serializedAdditionalRawData;
-
-        internal ModelWithRequiredNullableProperties(int? requiredNullablePrimitive, StringExtensibleEnum? requiredExtensibleEnum, StringFixedEnum? requiredFixedEnum, IDictionary<string, BinaryData> serializedAdditionalRawData)
-        {
-            RequiredNullablePrimitive = requiredNullablePrimitive;
-            RequiredExtensibleEnum = requiredExtensibleEnum;
-            RequiredFixedEnum = requiredFixedEnum;
-            _serializedAdditionalRawData = serializedAdditionalRawData;
-        }
-
         internal ModelWithRequiredNullableProperties()
         {
         }
diff --git a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ModelWithRequiredNullableProperties.cs b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ModelWithRequiredNullableProperties.cs
index e84593a20e9..cc3b5f7026b 100644
--- a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ModelWithRequiredNullableProperties.cs
+++ b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ModelWithRequiredNullableProperties.cs
@@ -2,11 +2,17 @@
 
 #nullable disable
 
+using System;
+using System.Collections.Generic;
+
 namespace UnbrandedTypeSpec.Models
 {
     /// <summary> A model with a few required nullable properties. </summary>
     public partial class ModelWithRequiredNullableProperties
     {
+        /// <summary> Keeps track of any properties unknown to the library. </summary>
+        private IDictionary<string, BinaryData> _serializedAdditionalRawData;
+
         /// <summary> Initializes a new instance of <see cref="ModelWithRequiredNullableProperties"/>. </summary>
         /// <param name="requiredNullablePrimitive"> required nullable primitive type. </param>
         /// <param name="requiredExtensibleEnum"> required nullable extensible enum type. </param>
@@ -18,6 +24,14 @@ public ModelWithRequiredNullableProperties(int? requiredNullablePrimitive, Strin
             RequiredFixedEnum = requiredFixedEnum;
         }
 
+        internal ModelWithRequiredNullableProperties(int? requiredNullablePrimitive, StringExtensibleEnum? requiredExtensibleEnum, StringFixedEnum? requiredFixedEnum, IDictionary<string, BinaryData> serializedAdditionalRawData)
+        {
+            RequiredNullablePrimitive = requiredNullablePrimitive;
+            RequiredExtensibleEnum = requiredExtensibleEnum;
+            RequiredFixedEnum = requiredFixedEnum;
+            _serializedAdditionalRawData = serializedAdditionalRawData;
+        }
+
         /// <summary> required nullable primitive type. </summary>
         public int? RequiredNullablePrimitive { get; set; }
 
diff --git a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ProjectedModel.Serialization.cs b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ProjectedModel.Serialization.cs
index 0cd9837d553..edae0338742 100644
--- a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ProjectedModel.Serialization.cs
+++ b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ProjectedModel.Serialization.cs
@@ -14,15 +14,6 @@ namespace UnbrandedTypeSpec.Models
     /// <summary></summary>
     public partial class ProjectedModel : IJsonModel<ProjectedModel>
     {
-        /// <summary> Keeps track of any properties unknown to the library. </summary>
-        private IDictionary<string, BinaryData> _serializedAdditionalRawData;
-
-        internal ProjectedModel(string name, IDictionary<string, BinaryData> serializedAdditionalRawData)
-        {
-            Name = name;
-            _serializedAdditionalRawData = serializedAdditionalRawData;
-        }
-
         internal ProjectedModel()
         {
         }
diff --git a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ProjectedModel.cs b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ProjectedModel.cs
index df2d716f954..243219cc974 100644
--- a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ProjectedModel.cs
+++ b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ProjectedModel.cs
@@ -2,16 +2,28 @@
 
 #nullable disable
 
+using System;
+using System.Collections.Generic;
+
 namespace UnbrandedTypeSpec.Models
 {
     /// <summary> this is a model with a projected name. </summary>
     public partial class ProjectedModel
     {
+        /// <summary> Keeps track of any properties unknown to the library. </summary>
+        private IDictionary<string, BinaryData> _serializedAdditionalRawData;
+
         internal ProjectedModel(string name)
         {
             Name = name;
         }
 
+        internal ProjectedModel(string name, IDictionary<string, BinaryData> serializedAdditionalRawData)
+        {
+            Name = name;
+            _serializedAdditionalRawData = serializedAdditionalRawData;
+        }
+
         /// <summary> name of the ModelWithProjectedName. </summary>
         public string Name { get; set; }
     }
diff --git a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ProjectedNameModelRequest.Serialization.cs b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ProjectedNameModelRequest.Serialization.cs
index 619c0189d22..84ca8f84e3f 100644
--- a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ProjectedNameModelRequest.Serialization.cs
+++ b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ProjectedNameModelRequest.Serialization.cs
@@ -14,15 +14,6 @@ namespace UnbrandedTypeSpec.Models
     /// <summary></summary>
     public partial class ProjectedNameModelRequest : IJsonModel<ProjectedNameModelRequest>
     {
-        /// <summary> Keeps track of any properties unknown to the library. </summary>
-        private IDictionary<string, BinaryData> _serializedAdditionalRawData;
-
-        internal ProjectedNameModelRequest(string name, IDictionary<string, BinaryData> serializedAdditionalRawData)
-        {
-            Name = name;
-            _serializedAdditionalRawData = serializedAdditionalRawData;
-        }
-
         internal ProjectedNameModelRequest()
         {
         }
diff --git a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ProjectedNameModelRequest.cs b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ProjectedNameModelRequest.cs
index a27f7d042f2..6c0c9696d56 100644
--- a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ProjectedNameModelRequest.cs
+++ b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ProjectedNameModelRequest.cs
@@ -2,16 +2,28 @@
 
 #nullable disable
 
+using System;
+using System.Collections.Generic;
+
 namespace UnbrandedTypeSpec.Models
 {
     /// <summary> The ProjectedNameModelRequest. </summary>
     public partial class ProjectedNameModelRequest
     {
+        /// <summary> Keeps track of any properties unknown to the library. </summary>
+        private IDictionary<string, BinaryData> _serializedAdditionalRawData;
+
         internal ProjectedNameModelRequest(string name)
         {
             Name = name;
         }
 
+        internal ProjectedNameModelRequest(string name, IDictionary<string, BinaryData> serializedAdditionalRawData)
+        {
+            Name = name;
+            _serializedAdditionalRawData = serializedAdditionalRawData;
+        }
+
         /// <summary> name of the ModelWithProjectedName. </summary>
         public string Name { get; set; }
     }
diff --git a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ReturnsAnonymousModelResponse.Serialization.cs b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ReturnsAnonymousModelResponse.Serialization.cs
index bc74620661e..6cef383a25e 100644
--- a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ReturnsAnonymousModelResponse.Serialization.cs
+++ b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ReturnsAnonymousModelResponse.Serialization.cs
@@ -14,14 +14,6 @@ namespace UnbrandedTypeSpec.Models
     /// <summary></summary>
     public partial class ReturnsAnonymousModelResponse : IJsonModel<ReturnsAnonymousModelResponse>
     {
-        /// <summary> Keeps track of any properties unknown to the library. </summary>
-        private IDictionary<string, BinaryData> _serializedAdditionalRawData;
-
-        internal ReturnsAnonymousModelResponse(IDictionary<string, BinaryData> serializedAdditionalRawData)
-        {
-            _serializedAdditionalRawData = serializedAdditionalRawData;
-        }
-
         void IJsonModel<ReturnsAnonymousModelResponse>.Write(Utf8JsonWriter writer, ModelReaderWriterOptions options)
         {
             writer.WriteStartObject();
diff --git a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ReturnsAnonymousModelResponse.cs b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ReturnsAnonymousModelResponse.cs
index d83a56f3465..d6210b21e66 100644
--- a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ReturnsAnonymousModelResponse.cs
+++ b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/ReturnsAnonymousModelResponse.cs
@@ -2,13 +2,24 @@
 
 #nullable disable
 
+using System;
+using System.Collections.Generic;
+
 namespace UnbrandedTypeSpec.Models
 {
     /// <summary> The ReturnsAnonymousModelResponse. </summary>
     public partial class ReturnsAnonymousModelResponse
     {
+        /// <summary> Keeps track of any properties unknown to the library. </summary>
+        private IDictionary<string, BinaryData> _serializedAdditionalRawData;
+
         internal ReturnsAnonymousModelResponse()
         {
         }
+
+        internal ReturnsAnonymousModelResponse(IDictionary<string, BinaryData> serializedAdditionalRawData)
+        {
+            _serializedAdditionalRawData = serializedAdditionalRawData;
+        }
     }
 }
diff --git a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/RoundTripModel.Serialization.cs b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/RoundTripModel.Serialization.cs
index 8cdfca05185..dae9fe23026 100644
--- a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/RoundTripModel.Serialization.cs
+++ b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/RoundTripModel.Serialization.cs
@@ -14,38 +14,6 @@ namespace UnbrandedTypeSpec.Models
     /// <summary></summary>
     public partial class RoundTripModel : IJsonModel<RoundTripModel>
     {
-        /// <summary> Keeps track of any properties unknown to the library. </summary>
-        private IDictionary<string, BinaryData> _serializedAdditionalRawData;
-
-        internal RoundTripModel(string requiredString, int requiredInt, IList<StringFixedEnum> requiredCollection, IDictionary<string, StringExtensibleEnum> requiredDictionary, Thing requiredModel, IntExtensibleEnum? intExtensibleEnum, IList<IntExtensibleEnum> intExtensibleEnumCollection, FloatExtensibleEnum? floatExtensibleEnum, FloatExtensibleEnumWithIntValue? floatExtensibleEnumWithIntValue, IList<FloatExtensibleEnum> floatExtensibleEnumCollection, FloatFixedEnum? floatFixedEnum, FloatFixedEnumWithIntValue? floatFixedEnumWithIntValue, IList<FloatFixedEnum> floatFixedEnumCollection, IntFixedEnum? intFixedEnum, IList<IntFixedEnum> intFixedEnumCollection, StringFixedEnum? stringFixedEnum, BinaryData requiredUnknown, BinaryData optionalUnknown, IDictionary<string, BinaryData> requiredRecordUnknown, IDictionary<string, BinaryData> optionalRecordUnknown, IReadOnlyDictionary<string, BinaryData> readOnlyRequiredRecordUnknown, IReadOnlyDictionary<string, BinaryData> readOnlyOptionalRecordUnknown, ModelWithRequiredNullableProperties modelWithRequiredNullable, BinaryData requiredBytes, IDictionary<string, BinaryData> serializedAdditionalRawData)
-        {
-            RequiredString = requiredString;
-            RequiredInt = requiredInt;
-            RequiredCollection = requiredCollection;
-            RequiredDictionary = requiredDictionary;
-            RequiredModel = requiredModel;
-            IntExtensibleEnum = intExtensibleEnum;
-            IntExtensibleEnumCollection = intExtensibleEnumCollection;
-            FloatExtensibleEnum = floatExtensibleEnum;
-            FloatExtensibleEnumWithIntValue = floatExtensibleEnumWithIntValue;
-            FloatExtensibleEnumCollection = floatExtensibleEnumCollection;
-            FloatFixedEnum = floatFixedEnum;
-            FloatFixedEnumWithIntValue = floatFixedEnumWithIntValue;
-            FloatFixedEnumCollection = floatFixedEnumCollection;
-            IntFixedEnum = intFixedEnum;
-            IntFixedEnumCollection = intFixedEnumCollection;
-            StringFixedEnum = stringFixedEnum;
-            RequiredUnknown = requiredUnknown;
-            OptionalUnknown = optionalUnknown;
-            RequiredRecordUnknown = requiredRecordUnknown;
-            OptionalRecordUnknown = optionalRecordUnknown;
-            ReadOnlyRequiredRecordUnknown = readOnlyRequiredRecordUnknown;
-            ReadOnlyOptionalRecordUnknown = readOnlyOptionalRecordUnknown;
-            ModelWithRequiredNullable = modelWithRequiredNullable;
-            RequiredBytes = requiredBytes;
-            _serializedAdditionalRawData = serializedAdditionalRawData;
-        }
-
         internal RoundTripModel()
         {
         }
diff --git a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/RoundTripModel.cs b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/RoundTripModel.cs
index 676eba05dfb..7bd748f8af0 100644
--- a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/RoundTripModel.cs
+++ b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/RoundTripModel.cs
@@ -13,6 +13,9 @@ namespace UnbrandedTypeSpec.Models
     /// <summary> this is a roundtrip model. </summary>
     public partial class RoundTripModel
     {
+        /// <summary> Keeps track of any properties unknown to the library. </summary>
+        private IDictionary<string, BinaryData> _serializedAdditionalRawData;
+
         /// <summary> Initializes a new instance of <see cref="RoundTripModel"/>. </summary>
         /// <param name="requiredString"> Required string, illustrating a reference type property. </param>
         /// <param name="requiredInt"> Required int, illustrating a value type property. </param>
@@ -53,6 +56,35 @@ public RoundTripModel(string requiredString, int requiredInt, IEnumerable<String
             RequiredBytes = requiredBytes;
         }
 
+        internal RoundTripModel(string requiredString, int requiredInt, IList<StringFixedEnum> requiredCollection, IDictionary<string, StringExtensibleEnum> requiredDictionary, Thing requiredModel, IntExtensibleEnum? intExtensibleEnum, IList<IntExtensibleEnum> intExtensibleEnumCollection, FloatExtensibleEnum? floatExtensibleEnum, FloatExtensibleEnumWithIntValue? floatExtensibleEnumWithIntValue, IList<FloatExtensibleEnum> floatExtensibleEnumCollection, FloatFixedEnum? floatFixedEnum, FloatFixedEnumWithIntValue? floatFixedEnumWithIntValue, IList<FloatFixedEnum> floatFixedEnumCollection, IntFixedEnum? intFixedEnum, IList<IntFixedEnum> intFixedEnumCollection, StringFixedEnum? stringFixedEnum, BinaryData requiredUnknown, BinaryData optionalUnknown, IDictionary<string, BinaryData> requiredRecordUnknown, IDictionary<string, BinaryData> optionalRecordUnknown, IReadOnlyDictionary<string, BinaryData> readOnlyRequiredRecordUnknown, IReadOnlyDictionary<string, BinaryData> readOnlyOptionalRecordUnknown, ModelWithRequiredNullableProperties modelWithRequiredNullable, BinaryData requiredBytes, IDictionary<string, BinaryData> serializedAdditionalRawData)
+        {
+            RequiredString = requiredString;
+            RequiredInt = requiredInt;
+            RequiredCollection = requiredCollection;
+            RequiredDictionary = requiredDictionary;
+            RequiredModel = requiredModel;
+            IntExtensibleEnum = intExtensibleEnum;
+            IntExtensibleEnumCollection = intExtensibleEnumCollection;
+            FloatExtensibleEnum = floatExtensibleEnum;
+            FloatExtensibleEnumWithIntValue = floatExtensibleEnumWithIntValue;
+            FloatExtensibleEnumCollection = floatExtensibleEnumCollection;
+            FloatFixedEnum = floatFixedEnum;
+            FloatFixedEnumWithIntValue = floatFixedEnumWithIntValue;
+            FloatFixedEnumCollection = floatFixedEnumCollection;
+            IntFixedEnum = intFixedEnum;
+            IntFixedEnumCollection = intFixedEnumCollection;
+            StringFixedEnum = stringFixedEnum;
+            RequiredUnknown = requiredUnknown;
+            OptionalUnknown = optionalUnknown;
+            RequiredRecordUnknown = requiredRecordUnknown;
+            OptionalRecordUnknown = optionalRecordUnknown;
+            ReadOnlyRequiredRecordUnknown = readOnlyRequiredRecordUnknown;
+            ReadOnlyOptionalRecordUnknown = readOnlyOptionalRecordUnknown;
+            ModelWithRequiredNullable = modelWithRequiredNullable;
+            RequiredBytes = requiredBytes;
+            _serializedAdditionalRawData = serializedAdditionalRawData;
+        }
+
         /// <summary> Required string, illustrating a reference type property. </summary>
         public string RequiredString { get; set; }
 
diff --git a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/Thing.Serialization.cs b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/Thing.Serialization.cs
index effd4fc052a..323d56091b3 100644
--- a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/Thing.Serialization.cs
+++ b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/Thing.Serialization.cs
@@ -14,27 +14,6 @@ namespace UnbrandedTypeSpec.Models
     /// <summary></summary>
     public partial class Thing : IJsonModel<Thing>
     {
-        /// <summary> Keeps track of any properties unknown to the library. </summary>
-        private IDictionary<string, BinaryData> _serializedAdditionalRawData;
-
-        internal Thing(string name, BinaryData requiredUnion, ThingRequiredLiteralString requiredLiteralString, ThingRequiredLiteralInt requiredLiteralInt, ThingRequiredLiteralFloat requiredLiteralFloat, bool requiredLiteralBool, ThingOptionalLiteralString? optionalLiteralString, ThingOptionalLiteralInt? optionalLiteralInt, ThingOptionalLiteralFloat? optionalLiteralFloat, bool? optionalLiteralBool, string requiredBadDescription, IList<int> optionalNullableList, IList<int> requiredNullableList, IDictionary<string, BinaryData> serializedAdditionalRawData)
-        {
-            Name = name;
-            RequiredUnion = requiredUnion;
-            RequiredLiteralString = requiredLiteralString;
-            RequiredLiteralInt = requiredLiteralInt;
-            RequiredLiteralFloat = requiredLiteralFloat;
-            RequiredLiteralBool = requiredLiteralBool;
-            OptionalLiteralString = optionalLiteralString;
-            OptionalLiteralInt = optionalLiteralInt;
-            OptionalLiteralFloat = optionalLiteralFloat;
-            OptionalLiteralBool = optionalLiteralBool;
-            RequiredBadDescription = requiredBadDescription;
-            OptionalNullableList = optionalNullableList;
-            RequiredNullableList = requiredNullableList;
-            _serializedAdditionalRawData = serializedAdditionalRawData;
-        }
-
         internal Thing()
         {
         }
diff --git a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/Thing.cs b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/Thing.cs
index 2b045c194d3..35c8e19739d 100644
--- a/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/Thing.cs
+++ b/packages/http-client-csharp/generator/TestProjects/Local/Unbranded-TypeSpec/src/Generated/Models/Thing.cs
@@ -13,6 +13,9 @@ namespace UnbrandedTypeSpec.Models
     /// <summary> A model with a few properties of literal types. </summary>
     public partial class Thing
     {
+        /// <summary> Keeps track of any properties unknown to the library. </summary>
+        private IDictionary<string, BinaryData> _serializedAdditionalRawData;
+
         /// <summary> Initializes a new instance of <see cref="Thing"/>. </summary>
         /// <param name="name"> name of the Thing. </param>
         /// <param name="requiredUnion"> required Union. </param>
@@ -32,6 +35,24 @@ public Thing(string name, BinaryData requiredUnion, string requiredBadDescriptio
             RequiredNullableList = requiredNullableList?.ToList();
         }
 
+        internal Thing(string name, BinaryData requiredUnion, ThingRequiredLiteralString requiredLiteralString, ThingRequiredLiteralInt requiredLiteralInt, ThingRequiredLiteralFloat requiredLiteralFloat, bool requiredLiteralBool, ThingOptionalLiteralString? optionalLiteralString, ThingOptionalLiteralInt? optionalLiteralInt, ThingOptionalLiteralFloat? optionalLiteralFloat, bool? optionalLiteralBool, string requiredBadDescription, IList<int> optionalNullableList, IList<int> requiredNullableList, IDictionary<string, BinaryData> serializedAdditionalRawData)
+        {
+            Name = name;
+            RequiredUnion = requiredUnion;
+            RequiredLiteralString = requiredLiteralString;
+            RequiredLiteralInt = requiredLiteralInt;
+            RequiredLiteralFloat = requiredLiteralFloat;
+            RequiredLiteralBool = requiredLiteralBool;
+            OptionalLiteralString = optionalLiteralString;
+            OptionalLiteralInt = optionalLiteralInt;
+            OptionalLiteralFloat = optionalLiteralFloat;
+            OptionalLiteralBool = optionalLiteralBool;
+            RequiredBadDescription = requiredBadDescription;
+            OptionalNullableList = optionalNullableList;
+            RequiredNullableList = requiredNullableList;
+            _serializedAdditionalRawData = serializedAdditionalRawData;
+        }
+
         /// <summary> name of the Thing. </summary>
         public string Name { get; set; }