diff --git a/docs/providers/azure-storage.md b/docs/providers/azure-storage.md
index cc9960838..a17444727 100644
--- a/docs/providers/azure-storage.md
+++ b/docs/providers/azure-storage.md
@@ -152,6 +152,15 @@ The Azure Storage provider creates these resources:
 | **Partitions Table** | `{taskhub}Partitions` | Partition leases (table manager) |
 | **Lease Blobs** | `{taskhub}-leases/` | Partition leases (blob manager) |
 
+### Queue Message Serialization
+
+The provider serializes the full `MessageData` envelope to JSON and measures its UTF-8 byte count before any Base64 encoding. Messages at or below 45 KiB (46,080 bytes) are sent inline using that same JSON. Larger messages are compressed and uploaded to blob storage; the queue receives a separately serialized blob-reference wrapper.
+
+This transport serialization is separate from the application input/output serialization performed by `DataConverter`. `AzureStorageOrchestrationServiceSettings.CustomMessageTypeBinder` configures type binding for queue messages. Its `ICustomTypeBinder.BindToName` implementation should return stable names for a given type. Serialization invocation counts are implementation details, not an API contract; custom binders, getters, and serialization callbacks on transport types must not depend on a particular number of passes for correctness.
+
+> [!NOTE]
+> The inline path reuses the JSON produced for the size check instead of serializing the full message a second time. This preserves the wire payload for stable messages with deterministic, side-effect-free serialization. Custom serialization logic that changes its output or relies on side effects across successive passes can observe a behavior change and should be reviewed when upgrading.
+
 ### Partitioning
 
 The Azure Storage provider uses **partitions** to distribute orchestration workloads across workers. Each partition corresponds to exactly one **control queue**.
diff --git a/src/DurableTask.AzureStorage/AzureStorageOrchestrationServiceSettings.cs b/src/DurableTask.AzureStorage/AzureStorageOrchestrationServiceSettings.cs
index bc5689e0e..5def0af60 100644
--- a/src/DurableTask.AzureStorage/AzureStorageOrchestrationServiceSettings.cs
+++ b/src/DurableTask.AzureStorage/AzureStorageOrchestrationServiceSettings.cs
@@ -239,8 +239,12 @@ public class AzureStorageOrchestrationServiceSettings
         public bool DisableExecutionStartedDeduplication { get; set; }
 
         /// <summary>
-        /// Gets or sets an optional custom type binder used when trying to deserialize queued messages.
+        /// Gets or sets an optional custom type binder used when serializing and deserializing queued messages.
         /// </summary>
+        /// <remarks>
+        /// Custom bindings must be stable and must not depend on serialization invocation counts.
+        /// See <see cref="ICustomTypeBinder.BindToName"/> for details.
+        /// </remarks>
         public ICustomTypeBinder? CustomMessageTypeBinder { get; set; }
 
         /// <summary>
diff --git a/src/DurableTask.AzureStorage/ICustomTypeBinder.cs b/src/DurableTask.AzureStorage/ICustomTypeBinder.cs
index 44e85fdd3..4f9b90b16 100644
--- a/src/DurableTask.AzureStorage/ICustomTypeBinder.cs
+++ b/src/DurableTask.AzureStorage/ICustomTypeBinder.cs
@@ -17,15 +17,20 @@ namespace DurableTask.AzureStorage
 {
     /// <summary>
     /// Abstraction to prevent surfacing the dynamic loading between System.Runtime.Serialization.SerializationBinder and Newtonsoft.Json.Serialization.ISerializationBinder
-    /// Used when deserializing QueueMessages to MessageData to allow providing custom type binding. 
-    /// Does not support custom bindings for DurableTask types
+    /// Used when serializing and deserializing queue messages to allow providing custom type binding.
+    /// Custom bindings for DurableTask types are not used during deserialization.
     /// </summary>
     public interface ICustomTypeBinder
     {
         /// <summary>
-        /// When implemented, controls the binding of a serialized object to a type.
+        /// When implemented, supplies the assembly and type names written during serialization.
         /// </summary>
-        /// <param name="serializedType">The type of the object the formatter creates a new instance of.</param>
+        /// <remarks>
+        /// Return stable names for a given type. The number of invocations is an implementation detail
+        /// and can vary with the message size, storage path, and serializer configuration.
+        /// Implementations must not depend on a particular invocation count for correctness.
+        /// </remarks>
+        /// <param name="serializedType">The type of the object being serialized.</param>
         /// <param name="assemblyName">Specifies the System.Reflection.Assembly name of the serialized object.</param>
         /// <param name="typeName">Specifies the System.Type name of the serialized object.</param>
         void BindToName(Type serializedType, out string assemblyName, out string typeName);
diff --git a/src/DurableTask.AzureStorage/MessageManager.cs b/src/DurableTask.AzureStorage/MessageManager.cs
index 1fc6d0785..e5809f618 100644
--- a/src/DurableTask.AzureStorage/MessageManager.cs
+++ b/src/DurableTask.AzureStorage/MessageManager.cs
@@ -119,7 +119,7 @@ public async Task<string> SerializeMessageDataAsync(MessageData messageData, Can
                 return Utils.SerializeToJson(serializer, wrapperMessageData);
             }
 
-            return Utils.SerializeToJson(serializer, messageData);
+            return rawContent;
         }
 
         /// <summary>
diff --git a/test/DurableTask.AzureStorage.Tests/MessageManagerTests.cs b/test/DurableTask.AzureStorage.Tests/MessageManagerTests.cs
index 008a9eac7..de86ca3d3 100644
--- a/test/DurableTask.AzureStorage.Tests/MessageManagerTests.cs
+++ b/test/DurableTask.AzureStorage.Tests/MessageManagerTests.cs
@@ -14,15 +14,20 @@
 namespace DurableTask.AzureStorage.Tests
 {
     using DurableTask.AzureStorage.Storage;
+    using DurableTask.Core;
     using DurableTask.Core.History;
     using Microsoft.VisualStudio.TestTools.UnitTesting;
     using Newtonsoft.Json;
     using System;
     using System.Collections.Generic;
+    using System.Text;
+    using System.Threading.Tasks;
 
     [TestClass]
     public class MessageManagerTests
     {
+        const int MaxStorageQueuePayloadSizeInBytes = 45 * 1024;
+
         [DataTestMethod]
         [DataRow("System.Collections.Generic.Dictionary`2[[System.String, System.Private.CoreLib],[System.String, System.Private.CoreLib]]")]
         [DataRow("System.Collections.Generic.Dictionary`2[[System.String, mscorlib],[System.String, mscorlib]]")]
@@ -69,6 +74,102 @@ public void DeserializesCustomTypes()
             Assert.AreEqual("tagValue", startedEvent.Tags["tag1"]);
         }
 
+        [DataTestMethod]
+        [DataRow(false)]
+        [DataRow(true)]
+        public async Task SerializeMessageDataAsync_InlinePayloadMatchesPreviousWirePayload(bool useDataContractSerialization)
+        {
+            var binder = new CustomNameTypeBinder();
+            var settings = new AzureStorageOrchestrationServiceSettings
+            {
+                CustomMessageTypeBinder = binder,
+                UseDataContractSerialization = useDataContractSerialization,
+            };
+            var manager = SetupMessageManager(settings, "$root");
+            MessageData message = CreateMessageData("inline payload");
+
+            string actualPayload = await manager.SerializeMessageDataAsync(message);
+            string previousWirePayload = SerializeUsingMessageSettings(
+                new AzureStorageOrchestrationServiceSettings
+                {
+                    CustomMessageTypeBinder = new CustomNameTypeBinder(),
+                    UseDataContractSerialization = useDataContractSerialization,
+                },
+                message);
+
+            Assert.AreEqual(previousWirePayload, actualPayload);
+            Assert.AreEqual(Encoding.UTF8.GetByteCount(previousWirePayload), message.TotalMessageSizeBytes);
+            Assert.AreEqual(MessageFormatFlags.InlineJson, manager.GetMessageFormatFlags(message));
+            Assert.IsNull(message.CompressedBlobName);
+            Assert.AreEqual(1, binder.MessageDataSerializationCount);
+            StringAssert.Contains(actualPayload, CustomNameTypeBinder.CustomAssemblyName);
+
+            MessageData roundTrippedMessage = manager.DeserializeMessageData(actualPayload);
+            Assert.AreEqual(message.ActivityId, roundTrippedMessage.ActivityId);
+            Assert.AreEqual(
+                ((GenericEvent)message.TaskMessage.Event).Data,
+                ((GenericEvent)roundTrippedMessage.TaskMessage.Event).Data);
+        }
+
+        [DataTestMethod]
+        [DataRow(false, 0)]
+        [DataRow(false, 1)]
+        [DataRow(true, 0)]
+        [DataRow(true, 1)]
+        public async Task SerializeMessageDataAsync_UsesExpectedStoragePathAtThreshold(
+            bool useDataContractSerialization,
+            int bytesOverThreshold)
+        {
+            var settings = new AzureStorageOrchestrationServiceSettings
+            {
+                UseDataContractSerialization = useDataContractSerialization,
+            };
+            string containerName = $"message-manager-{Guid.NewGuid():N}";
+            var manager = SetupMessageManager(settings, containerName);
+            int targetSize = MaxStorageQueuePayloadSizeInBytes + bytesOverThreshold;
+            MessageData message = CreateMessageDataWithSerializedSize(settings, targetSize);
+            string fullMessagePayload = SerializeUsingMessageSettings(settings, message);
+
+            try
+            {
+                string queuePayload = await manager.SerializeMessageDataAsync(message);
+                MessageFormatFlags expectedFormat = bytesOverThreshold == 0
+                    ? MessageFormatFlags.InlineJson
+                    : MessageFormatFlags.StorageBlob;
+
+                Assert.AreEqual(targetSize, message.TotalMessageSizeBytes);
+                Assert.AreEqual(expectedFormat, manager.GetMessageFormatFlags(message));
+
+                if (expectedFormat == MessageFormatFlags.InlineJson)
+                {
+                    Assert.AreEqual(fullMessagePayload, queuePayload);
+                    Assert.IsNull(message.CompressedBlobName);
+                }
+                else
+                {
+                    string expectedWrapperPayload = SerializeUsingMessageSettings(
+                        settings,
+                        new MessageData { CompressedBlobName = message.CompressedBlobName });
+                    Assert.AreEqual(expectedWrapperPayload, queuePayload);
+
+                    MessageData wrapper = manager.DeserializeMessageData(queuePayload);
+                    Assert.IsNull(wrapper.TaskMessage);
+                    Assert.IsFalse(string.IsNullOrWhiteSpace(wrapper.CompressedBlobName));
+                    Assert.AreEqual(message.CompressedBlobName, wrapper.CompressedBlobName);
+
+                    string storedPayload = await manager.DownloadAndDecompressAsBytesAsync(wrapper.CompressedBlobName);
+                    Assert.AreEqual(fullMessagePayload, storedPayload);
+                }
+            }
+            finally
+            {
+                if (bytesOverThreshold > 0)
+                {
+                    await manager.DeleteContainerAsync();
+                }
+            }
+        }
+
         [DataTestMethod]
         [DataRow("blob.bin", "blob.bin")]
         [DataRow("@#$%!", "%40%23%24%25%21")]
@@ -94,17 +195,108 @@ private string GetMessage(string dictionaryType)
 
         private MessageManager SetupMessageManager(ICustomTypeBinder binder)
         {
-            var azureStorageClient = new AzureStorageClient(
-                new AzureStorageOrchestrationServiceSettings
-                {
-                    StorageAccountClientProvider = new StorageAccountClientProvider("UseDevelopmentStorage=true"),
-                });
-
-            return new MessageManager(
+            return SetupMessageManager(
                 new AzureStorageOrchestrationServiceSettings { CustomMessageTypeBinder = binder },
-                azureStorageClient,
                 "$root");
         }
+
+        private static MessageManager SetupMessageManager(
+            AzureStorageOrchestrationServiceSettings settings,
+            string containerName)
+        {
+            settings.StorageAccountClientProvider =
+                new StorageAccountClientProvider(TestHelpers.GetTestStorageAccountConnectionString());
+            var azureStorageClient = new AzureStorageClient(settings);
+            return new MessageManager(settings, azureStorageClient, containerName);
+        }
+
+        private static MessageData CreateMessageData(string payload)
+        {
+            var orchestrationInstance = new OrchestrationInstance
+            {
+                InstanceId = "message-manager-instance",
+                ExecutionId = "message-manager-execution",
+            };
+            var taskMessage = new TaskMessage
+            {
+                Event = new GenericEvent(1, payload),
+                OrchestrationInstance = orchestrationInstance,
+                SequenceNumber = 42,
+            };
+
+            return new MessageData(
+                taskMessage,
+                Guid.Parse("55f31df8-9abb-4d86-a197-78fd0908efcf"),
+                "message-manager-queue",
+                orchestrationEpisode: 3,
+                sender: orchestrationInstance)
+            {
+                SequenceNumber = 43,
+                SerializableTraceContext = "trace-context",
+            };
+        }
+
+        private static MessageData CreateMessageDataWithSerializedSize(
+            AzureStorageOrchestrationServiceSettings settings,
+            int targetSize)
+        {
+            MessageData message = CreateMessageData(string.Empty);
+            int emptyPayloadSize = Encoding.UTF8.GetByteCount(SerializeUsingMessageSettings(settings, message));
+            Assert.IsTrue(targetSize >= emptyPayloadSize);
+
+            ((GenericEvent)message.TaskMessage.Event).Data = new string('x', targetSize - emptyPayloadSize);
+            int actualSize = Encoding.UTF8.GetByteCount(SerializeUsingMessageSettings(settings, message));
+            Assert.AreEqual(targetSize, actualSize);
+            return message;
+        }
+
+        private static string SerializeUsingMessageSettings(
+            AzureStorageOrchestrationServiceSettings settings,
+            MessageData message)
+        {
+            var serializerSettings = new JsonSerializerSettings
+            {
+                TypeNameHandling = TypeNameHandling.Objects,
+                SerializationBinder = new TypeNameSerializationBinder(settings.CustomMessageTypeBinder),
+            };
+
+            if (settings.UseDataContractSerialization)
+            {
+                serializerSettings.Converters.Add(new DataContractJsonConverter());
+            }
+
+            return Utils.SerializeToJson(JsonSerializer.Create(serializerSettings), message);
+        }
+    }
+
+    internal class CustomNameTypeBinder : ICustomTypeBinder
+    {
+        public const string CustomAssemblyName = "MessageManagerTests.CustomAssembly";
+        readonly Dictionary<string, Type> serializedTypes = new Dictionary<string, Type>();
+
+        public int MessageDataSerializationCount { get; private set; }
+
+        public void BindToName(Type serializedType, out string assemblyName, out string typeName)
+        {
+            assemblyName = CustomAssemblyName;
+            typeName = serializedType.FullName!;
+            this.serializedTypes[typeName] = serializedType;
+
+            if (serializedType == typeof(MessageData))
+            {
+                this.MessageDataSerializationCount++;
+            }
+        }
+
+        public Type BindToType(string assemblyName, string typeName)
+        {
+            if (this.serializedTypes.TryGetValue(typeName, out Type? serializedType))
+            {
+                return serializedType;
+            }
+
+            throw new JsonSerializationException($"Unknown serialized type '{typeName}'.");
+        }
     }
 
     internal class KnownTypeBinder : ICustomTypeBinder