diff --git a/sdk/src/Services/S3/Custom/Transfer/Internal/BufferedDownloadConfiguration.cs b/sdk/src/Services/S3/Custom/Transfer/Internal/BufferedDownloadConfiguration.cs
index 43121706d940..867774da8810 100644
--- a/sdk/src/Services/S3/Custom/Transfer/Internal/BufferedDownloadConfiguration.cs
+++ b/sdk/src/Services/S3/Custom/Transfer/Internal/BufferedDownloadConfiguration.cs
@@ -30,9 +30,9 @@ namespace Amazon.S3.Transfer.Internal
     internal class BufferedDownloadConfiguration : DownloadManagerConfiguration
     {
         /// <summary>
-        /// Maximum parts to keep in memory simultaneously.
+        /// Maximum parts to keep in memory simultaneously. When null, defaults to 1024.
         /// </summary>
-        public int MaxInMemoryParts { get; set; }
+        public int? MaxInMemoryParts { get; set; }
         
         /// <summary>
         /// Buffer size for I/O operations.
@@ -48,20 +48,20 @@ internal class BufferedDownloadConfiguration : DownloadManagerConfiguration
         /// Creates a BufferedDownloadConfiguration with the specified configuration values.
         /// </summary>
         /// <param name="concurrentServiceRequests">Maximum concurrent HTTP requests for downloading parts.</param>
-        /// <param name="maxInMemoryParts">Maximum number of parts to keep in memory simultaneously.</param>
+        /// <param name="maxInMemoryParts">Maximum number of parts to keep in memory simultaneously. When null, defaults to 1024.</param>
         /// <param name="bufferSize">Buffer size used for optimal I/O operations.</param>
         /// <param name="targetPartSizeBytes">Target size for each part in bytes.</param>
         /// <param name="chunkBufferSize">Optional chunk buffer size for ChunkedBufferStream. When null, defaults to 64KB.</param>
         /// <exception cref="ArgumentOutOfRangeException">Thrown when any parameter is less than or equal to 0.</exception>
         public BufferedDownloadConfiguration(
             int concurrentServiceRequests,
-            int maxInMemoryParts,
+            int? maxInMemoryParts,
             int bufferSize,
             long targetPartSizeBytes,
             int? chunkBufferSize = null)
             : base(concurrentServiceRequests, targetPartSizeBytes)
         {
-            if (maxInMemoryParts <= 0)
+            if (maxInMemoryParts.HasValue && maxInMemoryParts.Value <= 0)
                 throw new ArgumentOutOfRangeException(nameof(maxInMemoryParts), "Must be greater than 0");
             if (bufferSize <= 0)
                 throw new ArgumentOutOfRangeException(nameof(bufferSize), "Must be greater than 0");
diff --git a/sdk/src/Services/S3/Custom/Transfer/Internal/PartBufferManager.cs b/sdk/src/Services/S3/Custom/Transfer/Internal/PartBufferManager.cs
index a27622ea4377..b6b5cd455c36 100644
--- a/sdk/src/Services/S3/Custom/Transfer/Internal/PartBufferManager.cs
+++ b/sdk/src/Services/S3/Custom/Transfer/Internal/PartBufferManager.cs
@@ -189,14 +189,17 @@ public PartBufferManager(BufferedDownloadConfiguration config)
             if (config == null)
                 throw new ArgumentNullException(nameof(config));
             
+            // Resolve null MaxInMemoryParts to default value of 1024
+            var maxInMemoryParts = config.MaxInMemoryParts ?? 1024;
+            
             _partDataSources = new ConcurrentDictionary<int, IPartDataSource>();
             _bufferSpaceAvailable = new SemaphoreSlim(
-                config.MaxInMemoryParts,  // initialCount
-                config.MaxInMemoryParts   // maxCount - prevents exceeding configured limit
+                maxInMemoryParts,  // initialCount
+                maxInMemoryParts   // maxCount - prevents exceeding configured limit
             );
             _partAvailable = new AutoResetEvent(false);
             
-            _logger.DebugFormat("PartBufferManager initialized with MaxInMemoryParts={0}", config.MaxInMemoryParts);
+            _logger.DebugFormat("PartBufferManager initialized with MaxInMemoryParts={0}", maxInMemoryParts);
         }
 
         /// <inheritdoc/>
diff --git a/sdk/src/Services/S3/Custom/Transfer/TransferUtilityOpenStreamRequest.cs b/sdk/src/Services/S3/Custom/Transfer/TransferUtilityOpenStreamRequest.cs
index a9ed2b468b8b..c36e8c79def5 100644
--- a/sdk/src/Services/S3/Custom/Transfer/TransferUtilityOpenStreamRequest.cs
+++ b/sdk/src/Services/S3/Custom/Transfer/TransferUtilityOpenStreamRequest.cs
@@ -32,22 +32,17 @@ namespace Amazon.S3.Transfer
     /// </summary>
     public class TransferUtilityOpenStreamRequest : BaseDownloadRequest
     {
-        private int _maxInMemoryParts = 1024;
-
         /// <summary>
         /// Gets or sets the maximum number of parts to buffer in memory during multipart downloads.
-        /// The default value is 1024.
+        /// When null, defaults to 1024.
         /// </summary>
         /// <remarks>
         /// This property controls memory usage during streaming downloads. When combined with the 
         /// default part size of 8MB, the default value of 1024 parts allows up to 8GB of memory usage.
         /// Adjust this value based on your application's memory constraints and performance requirements.
+        /// Set to null to use the default value of 1024.
         /// </remarks>
-        public int MaxInMemoryParts
-        {
-            get { return this._maxInMemoryParts; }
-            set { this._maxInMemoryParts = value; }
-        }
+        public int? MaxInMemoryParts { get; set; }
 
         /// <summary>
         /// Gets or sets the chunk buffer size (in bytes) used for buffering out-of-order parts during multipart downloads.
diff --git a/sdk/test/Services/S3/UnitTests/Custom/BufferedDownloadConfigurationTests.cs b/sdk/test/Services/S3/UnitTests/Custom/BufferedDownloadConfigurationTests.cs
index 3574aa24914c..50eba721ff7d 100644
--- a/sdk/test/Services/S3/UnitTests/Custom/BufferedDownloadConfigurationTests.cs
+++ b/sdk/test/Services/S3/UnitTests/Custom/BufferedDownloadConfigurationTests.cs
@@ -18,7 +18,7 @@ public void Constructor_WithValidParameters_CreatesConfiguration()
         {
             // Arrange
             int concurrentRequests = 10;
-            int maxInMemoryParts = 5;
+            int? maxInMemoryParts = 5;
             int bufferSize = 8192;
             long targetPartSize = 8 * 1024 * 1024; // 8MB
 
@@ -38,7 +38,7 @@ public void Constructor_WithChunkBufferSize_SetsProperty()
         {
             // Arrange
             int concurrentRequests = 10;
-            int maxInMemoryParts = 5;
+            int? maxInMemoryParts = 5;
             int bufferSize = 8192;
             long targetPartSize = 8 * 1024 * 1024; // 8MB
             int chunkBufferSize = 32 * 1024; // 32KB
@@ -59,7 +59,7 @@ public void Constructor_WithNullChunkBufferSize_LeavesPropertyNull()
         {
             // Arrange
             int concurrentRequests = 10;
-            int maxInMemoryParts = 5;
+            int? maxInMemoryParts = 5;
             int bufferSize = 8192;
             long targetPartSize = 8 * 1024 * 1024; // 8MB
 
@@ -162,6 +162,22 @@ public void Constructor_WithZeroConcurrentRequests_ThrowsException()
             var config = new BufferedDownloadConfiguration(0, 5, 8192, 8 * 1024 * 1024);
         }
 
+        [TestMethod]
+        public void Constructor_WithNullMaxInMemoryParts_AcceptsValue()
+        {
+            // Arrange
+            int concurrentRequests = 10;
+            int? maxInMemoryParts = null;
+            int bufferSize = 8192;
+            long targetPartSize = 8 * 1024 * 1024; // 8MB
+
+            // Act
+            var config = new BufferedDownloadConfiguration(concurrentRequests, maxInMemoryParts, bufferSize, targetPartSize);
+
+            // Assert
+            Assert.IsNull(config.MaxInMemoryParts);
+        }
+
         [TestMethod]
         [ExpectedException(typeof(ArgumentOutOfRangeException))]
         public void Constructor_WithNegativeMaxInMemoryParts_ThrowsException()