diff --git a/sdk/core/System.ClientModel/api/System.ClientModel.net6.0.cs b/sdk/core/System.ClientModel/api/System.ClientModel.net6.0.cs
index 3edacd35c1d4..ebb1d752e648 100644
--- a/sdk/core/System.ClientModel/api/System.ClientModel.net6.0.cs
+++ b/sdk/core/System.ClientModel/api/System.ClientModel.net6.0.cs
@@ -107,6 +107,10 @@ protected virtual void OnSendingRequest(System.ClientModel.Primitives.PipelineMe
         protected sealed override void ProcessCore(System.ClientModel.Primitives.PipelineMessage message) { }
         protected sealed override System.Threading.Tasks.ValueTask ProcessCoreAsync(System.ClientModel.Primitives.PipelineMessage message) { throw null; }
     }
+    public partial interface IJsonModel
+    {
+        System.Collections.Generic.IDictionary<string, object> AdditionalProperties { get; }
+    }
     public partial interface IJsonModel<out T> : System.ClientModel.Primitives.IPersistableModel<T>
     {
         T Create(ref System.Text.Json.Utf8JsonReader reader, System.ClientModel.Primitives.ModelReaderWriterOptions options);
@@ -118,6 +122,21 @@ public partial interface IPersistableModel<out T>
         string GetFormatFromOptions(System.ClientModel.Primitives.ModelReaderWriterOptions options);
         System.BinaryData Write(System.ClientModel.Primitives.ModelReaderWriterOptions options);
     }
+    public abstract partial class JsonModel<T> : System.ClientModel.Primitives.IJsonModel, System.ClientModel.Primitives.IJsonModel<T>, System.ClientModel.Primitives.IPersistableModel<T>
+    {
+        protected JsonModel() { }
+        System.Collections.Generic.IDictionary<string, object> System.ClientModel.Primitives.IJsonModel.AdditionalProperties { get { throw null; } }
+        protected abstract T CreateCore(ref System.Text.Json.Utf8JsonReader reader, System.ClientModel.Primitives.ModelReaderWriterOptions options);
+        protected virtual string GetFormatFromOptionsCore(System.ClientModel.Primitives.ModelReaderWriterOptions options) { throw null; }
+        protected void ReadUnknownProperty(ref System.Text.Json.Utf8JsonReader reader, System.ClientModel.Primitives.ModelReaderWriterOptions options) { }
+        T System.ClientModel.Primitives.IJsonModel<T>.Create(ref System.Text.Json.Utf8JsonReader reader, System.ClientModel.Primitives.ModelReaderWriterOptions options) { throw null; }
+        void System.ClientModel.Primitives.IJsonModel<T>.Write(System.Text.Json.Utf8JsonWriter writer, System.ClientModel.Primitives.ModelReaderWriterOptions options) { }
+        T System.ClientModel.Primitives.IPersistableModel<T>.Create(System.BinaryData data, System.ClientModel.Primitives.ModelReaderWriterOptions options) { throw null; }
+        string System.ClientModel.Primitives.IPersistableModel<T>.GetFormatFromOptions(System.ClientModel.Primitives.ModelReaderWriterOptions options) { throw null; }
+        System.BinaryData System.ClientModel.Primitives.IPersistableModel<T>.Write(System.ClientModel.Primitives.ModelReaderWriterOptions options) { throw null; }
+        protected abstract void WriteCore(System.Text.Json.Utf8JsonWriter writer, System.ClientModel.Primitives.ModelReaderWriterOptions options);
+        protected void WriteUnknownProperties(System.Text.Json.Utf8JsonWriter writer, System.ClientModel.Primitives.ModelReaderWriterOptions options) { }
+    }
     public static partial class ModelReaderWriter
     {
         public static object? Read(System.BinaryData data, [System.Diagnostics.CodeAnalysis.DynamicallyAccessedMembersAttribute(System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.NonPublicConstructors | System.Diagnostics.CodeAnalysis.DynamicallyAccessedMemberTypes.PublicConstructors)] System.Type returnType, System.ClientModel.Primitives.ModelReaderWriterOptions? options = null) { throw null; }
diff --git a/sdk/core/System.ClientModel/api/System.ClientModel.netstandard2.0.cs b/sdk/core/System.ClientModel/api/System.ClientModel.netstandard2.0.cs
index 2367ba7f518d..775f20d55344 100644
--- a/sdk/core/System.ClientModel/api/System.ClientModel.netstandard2.0.cs
+++ b/sdk/core/System.ClientModel/api/System.ClientModel.netstandard2.0.cs
@@ -107,6 +107,10 @@ protected virtual void OnSendingRequest(System.ClientModel.Primitives.PipelineMe
         protected sealed override void ProcessCore(System.ClientModel.Primitives.PipelineMessage message) { }
         protected sealed override System.Threading.Tasks.ValueTask ProcessCoreAsync(System.ClientModel.Primitives.PipelineMessage message) { throw null; }
     }
+    public partial interface IJsonModel
+    {
+        System.Collections.Generic.IDictionary<string, object> AdditionalProperties { get; }
+    }
     public partial interface IJsonModel<out T> : System.ClientModel.Primitives.IPersistableModel<T>
     {
         T Create(ref System.Text.Json.Utf8JsonReader reader, System.ClientModel.Primitives.ModelReaderWriterOptions options);
@@ -118,6 +122,21 @@ public partial interface IPersistableModel<out T>
         string GetFormatFromOptions(System.ClientModel.Primitives.ModelReaderWriterOptions options);
         System.BinaryData Write(System.ClientModel.Primitives.ModelReaderWriterOptions options);
     }
+    public abstract partial class JsonModel<T> : System.ClientModel.Primitives.IJsonModel, System.ClientModel.Primitives.IJsonModel<T>, System.ClientModel.Primitives.IPersistableModel<T>
+    {
+        protected JsonModel() { }
+        System.Collections.Generic.IDictionary<string, object> System.ClientModel.Primitives.IJsonModel.AdditionalProperties { get { throw null; } }
+        protected abstract T CreateCore(ref System.Text.Json.Utf8JsonReader reader, System.ClientModel.Primitives.ModelReaderWriterOptions options);
+        protected virtual string GetFormatFromOptionsCore(System.ClientModel.Primitives.ModelReaderWriterOptions options) { throw null; }
+        protected void ReadUnknownProperty(ref System.Text.Json.Utf8JsonReader reader, System.ClientModel.Primitives.ModelReaderWriterOptions options) { }
+        T System.ClientModel.Primitives.IJsonModel<T>.Create(ref System.Text.Json.Utf8JsonReader reader, System.ClientModel.Primitives.ModelReaderWriterOptions options) { throw null; }
+        void System.ClientModel.Primitives.IJsonModel<T>.Write(System.Text.Json.Utf8JsonWriter writer, System.ClientModel.Primitives.ModelReaderWriterOptions options) { }
+        T System.ClientModel.Primitives.IPersistableModel<T>.Create(System.BinaryData data, System.ClientModel.Primitives.ModelReaderWriterOptions options) { throw null; }
+        string System.ClientModel.Primitives.IPersistableModel<T>.GetFormatFromOptions(System.ClientModel.Primitives.ModelReaderWriterOptions options) { throw null; }
+        System.BinaryData System.ClientModel.Primitives.IPersistableModel<T>.Write(System.ClientModel.Primitives.ModelReaderWriterOptions options) { throw null; }
+        protected abstract void WriteCore(System.Text.Json.Utf8JsonWriter writer, System.ClientModel.Primitives.ModelReaderWriterOptions options);
+        protected void WriteUnknownProperties(System.Text.Json.Utf8JsonWriter writer, System.ClientModel.Primitives.ModelReaderWriterOptions options) { }
+    }
     public static partial class ModelReaderWriter
     {
         public static object? Read(System.BinaryData data, System.Type returnType, System.ClientModel.Primitives.ModelReaderWriterOptions? options = null) { throw null; }
diff --git a/sdk/core/System.ClientModel/src/ModelReaderWriter/IJsonModel.cs b/sdk/core/System.ClientModel/src/ModelReaderWriter/IJsonModel.cs
index 0fc498a4da62..7c3237071a78 100644
--- a/sdk/core/System.ClientModel/src/ModelReaderWriter/IJsonModel.cs
+++ b/sdk/core/System.ClientModel/src/ModelReaderWriter/IJsonModel.cs
@@ -1,34 +1,13 @@
 // Copyright (c) Microsoft Corporation. All rights reserved.
 // Licensed under the MIT License.
 
-using System.Text.Json;
+using System.Collections.Generic;
 
 namespace System.ClientModel.Primitives;
 
-/// <summary>
-/// Allows an object to control its own JSON writing and reading.
-/// </summary>
-/// <typeparam name="T">The type the model can be converted into.</typeparam>
-public interface IJsonModel<out T> : IPersistableModel<T>
+#pragma warning disable CS1591 // public XML comments
+public interface IJsonModel
 {
-    /// <summary>
-    /// Writes the model to the provided <see cref="Utf8JsonWriter"/>.
-    /// </summary>
-    /// <param name="writer">The <see cref="Utf8JsonWriter"/> to write into.</param>
-    /// <param name="options">The <see cref="ModelReaderWriterOptions"/> to use.</param>
-    /// <exception cref="FormatException">If the model does not support the requested <see cref="ModelReaderWriterOptions.Format"/>.</exception>
-#pragma warning disable AZC0014 // Avoid using banned types in public API
-    void Write(Utf8JsonWriter writer, ModelReaderWriterOptions options);
-#pragma warning restore AZC0014 // Avoid using banned types in public API
-
-    /// <summary>
-    /// Reads one JSON value (including objects or arrays) from the provided reader and converts it to a model.
-    /// </summary>
-    /// <param name="reader">The <see cref="Utf8JsonReader"/> to read.</param>
-    /// <param name="options">The <see cref="ModelReaderWriterOptions"/> to use.</param>
-    /// <returns>A <typeparamref name="T"/> representation of the JSON value.</returns>
-    /// <exception cref="FormatException">If the model does not support the requested <see cref="ModelReaderWriterOptions.Format"/>.</exception>
-#pragma warning disable AZC0014 // Avoid using banned types in public API
-    T Create(ref Utf8JsonReader reader, ModelReaderWriterOptions options);
-#pragma warning restore AZC0014 // Avoid using banned types in public API
+    IDictionary<string, object> AdditionalProperties { get; }
 }
+#pragma warning restore CS1591 // public XML comments
diff --git a/sdk/core/System.ClientModel/src/ModelReaderWriter/IJsonModelOfT.cs b/sdk/core/System.ClientModel/src/ModelReaderWriter/IJsonModelOfT.cs
new file mode 100644
index 000000000000..0fc498a4da62
--- /dev/null
+++ b/sdk/core/System.ClientModel/src/ModelReaderWriter/IJsonModelOfT.cs
@@ -0,0 +1,34 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+using System.Text.Json;
+
+namespace System.ClientModel.Primitives;
+
+/// <summary>
+/// Allows an object to control its own JSON writing and reading.
+/// </summary>
+/// <typeparam name="T">The type the model can be converted into.</typeparam>
+public interface IJsonModel<out T> : IPersistableModel<T>
+{
+    /// <summary>
+    /// Writes the model to the provided <see cref="Utf8JsonWriter"/>.
+    /// </summary>
+    /// <param name="writer">The <see cref="Utf8JsonWriter"/> to write into.</param>
+    /// <param name="options">The <see cref="ModelReaderWriterOptions"/> to use.</param>
+    /// <exception cref="FormatException">If the model does not support the requested <see cref="ModelReaderWriterOptions.Format"/>.</exception>
+#pragma warning disable AZC0014 // Avoid using banned types in public API
+    void Write(Utf8JsonWriter writer, ModelReaderWriterOptions options);
+#pragma warning restore AZC0014 // Avoid using banned types in public API
+
+    /// <summary>
+    /// Reads one JSON value (including objects or arrays) from the provided reader and converts it to a model.
+    /// </summary>
+    /// <param name="reader">The <see cref="Utf8JsonReader"/> to read.</param>
+    /// <param name="options">The <see cref="ModelReaderWriterOptions"/> to use.</param>
+    /// <returns>A <typeparamref name="T"/> representation of the JSON value.</returns>
+    /// <exception cref="FormatException">If the model does not support the requested <see cref="ModelReaderWriterOptions.Format"/>.</exception>
+#pragma warning disable AZC0014 // Avoid using banned types in public API
+    T Create(ref Utf8JsonReader reader, ModelReaderWriterOptions options);
+#pragma warning restore AZC0014 // Avoid using banned types in public API
+}
diff --git a/sdk/core/System.ClientModel/src/ModelReaderWriter/IPersistableModel.cs b/sdk/core/System.ClientModel/src/ModelReaderWriter/IPersistableModelOfT.cs
similarity index 100%
rename from sdk/core/System.ClientModel/src/ModelReaderWriter/IPersistableModel.cs
rename to sdk/core/System.ClientModel/src/ModelReaderWriter/IPersistableModelOfT.cs
diff --git a/sdk/core/System.ClientModel/src/ModelReaderWriter/JsonModelOfT.cs b/sdk/core/System.ClientModel/src/ModelReaderWriter/JsonModelOfT.cs
new file mode 100644
index 000000000000..2e3e663ece99
--- /dev/null
+++ b/sdk/core/System.ClientModel/src/ModelReaderWriter/JsonModelOfT.cs
@@ -0,0 +1,175 @@
+// Copyright (c) Microsoft Corporation. All rights reserved.
+// Licensed under the MIT License.
+
+using System.Collections.Generic;
+using System.IO;
+using System.Text.Json;
+
+namespace System.ClientModel.Primitives;
+
+#pragma warning disable CS1591 // public XML comments
+public abstract class JsonModel<T> : IJsonModel, IJsonModel<T>
+{
+    private Dictionary<string, object>? _unknownProperties;
+
+    IDictionary<string, object> IJsonModel.AdditionalProperties
+        => _unknownProperties ??= new();
+
+#pragma warning disable AZC0014 // Avoid using banned types in public API
+    protected abstract T CreateCore(ref Utf8JsonReader reader, ModelReaderWriterOptions options);
+
+    protected abstract void WriteCore(Utf8JsonWriter writer, ModelReaderWriterOptions options);
+#pragma warning restore AZC0014 // Avoid using banned types in public API
+
+    T IJsonModel<T>.Create(ref Utf8JsonReader reader, ModelReaderWriterOptions options)
+        => CreateCore(ref reader, options);
+
+    T IPersistableModel<T>.Create(BinaryData data, ModelReaderWriterOptions options)
+    {
+        var pm = this as IJsonModel<T>;
+        var reader = new Utf8JsonReader(data);
+        return pm.Create(ref reader, options);
+    }
+
+    string IPersistableModel<T>.GetFormatFromOptions(ModelReaderWriterOptions options)
+        => GetFormatFromOptionsCore(options);
+
+    protected virtual string GetFormatFromOptionsCore(ModelReaderWriterOptions options)
+    {
+        if (options.Format == "W")
+            return "J";
+
+        throw new NotSupportedException();
+    }
+
+    void IJsonModel<T>.Write(Utf8JsonWriter writer, ModelReaderWriterOptions options)
+        => WriteCore(writer, options);
+
+    BinaryData IPersistableModel<T>.Write(ModelReaderWriterOptions options)
+    {
+        using var stream = new MemoryStream();
+        using var writer = new Utf8JsonWriter(stream);
+
+        var jsonModel = this as IJsonModel<T>;
+        jsonModel.Write(writer, options);
+        stream.Position = 0;
+        // TODO: flush?
+
+        return BinaryData.FromStream(stream);
+    }
+
+    private static BinaryData ReadUnknownValue(ref Utf8JsonReader reader)
+    {
+        var stream = new MemoryStream();
+        int depth = 0;
+#if NET6_0_OR_GREATER
+        bool writeComma = false;
+#endif
+
+        // TODO: netstandard2.0
+
+        while (true)
+        {
+            if (!reader.Read())
+                throw new Exception();
+
+            switch (reader.TokenType)
+            {
+                case JsonTokenType.String:
+                    if (depth == 0)
+                    {
+                        return new BinaryData(reader.ValueSpan.ToArray());
+                    }
+#if NET6_0_OR_GREATER
+                    stream.Write("\""u8);
+                    stream.Write(reader.ValueSpan);
+                    stream.Write("\""u8);
+                    writeComma = true;
+#endif
+                    break;
+                case JsonTokenType.Number:
+                    if (depth == 0)
+                    {
+                        return new BinaryData(reader.ValueSpan.ToArray());
+                    }
+#if NET6_0_OR_GREATER
+                    stream.Write(reader.ValueSpan);
+                    writeComma = true;
+#endif
+                    break;
+                case JsonTokenType.EndObject:
+                case JsonTokenType.EndArray:
+#if NET6_0_OR_GREATER
+                    stream.Write(reader.ValueSpan);
+#endif
+                    depth--;
+                    if (depth == 0)
+                    {
+                        stream.Position = 0;
+                        return BinaryData.FromStream(stream);
+                    }
+                    break;
+                case JsonTokenType.StartObject:
+                case JsonTokenType.StartArray:
+                    depth++;
+#if NET6_0_OR_GREATER
+                    stream.Write(reader.ValueSpan);
+#endif
+                    break;
+                case JsonTokenType.PropertyName:
+#if NET6_0_OR_GREATER
+                    if (writeComma)
+                    {
+                        stream.Write(",\n"u8);
+                        writeComma = false;
+                    }
+                    stream.Write("\""u8);
+                    stream.Write(reader.ValueSpan);
+                    stream.Write("\":"u8);
+#endif
+                    break;
+
+                default:
+                    throw new NotImplementedException();
+            }
+        }
+    }
+
+#pragma warning disable AZC0014 // Avoid using banned types in public API
+    protected void ReadUnknownProperty(ref Utf8JsonReader reader, ModelReaderWriterOptions options)
+#pragma warning restore AZC0014 // Avoid using banned types in public API
+    {
+        string name = reader.GetString()!;
+        BinaryData value = ReadUnknownValue(ref reader);
+        ((IJsonModel)this).AdditionalProperties.Add(name, value);
+    }
+
+#pragma warning disable AZC0014 // Avoid using banned types in public API
+    protected void WriteUnknownProperties(Utf8JsonWriter writer, ModelReaderWriterOptions options)
+#pragma warning restore AZC0014 // Avoid using banned types in public API
+    {
+        if (_unknownProperties != null)
+        {
+            foreach (var property in _unknownProperties)
+            {
+                // Skip non-serialized items for now
+                // TODO: serialize non-serialized items in some cases?
+                if (property.Value is not BinaryData serializedValue)
+                {
+                    continue;
+                }
+
+                writer.WritePropertyName(property.Key);
+#if NET6_0_OR_GREATER
+                writer.WriteRawValue(serializedValue);
+#else
+                using (JsonDocument document = JsonDocument.Parse(serializedValue))
+                {
+                    JsonSerializer.Serialize(writer, document.RootElement);
+                }
+#endif
+            }
+        }
+    }
+}
+#pragma warning restore CS1591 // public XML comments