diff --git a/sdk/src/Services/S3/Custom/Transfer/Internal/BufferedPartDataHandler.cs b/sdk/src/Services/S3/Custom/Transfer/Internal/BufferedPartDataHandler.cs
index ae55c6c2422c..02fb974c7f72 100644
--- a/sdk/src/Services/S3/Custom/Transfer/Internal/BufferedPartDataHandler.cs
+++ b/sdk/src/Services/S3/Custom/Transfer/Internal/BufferedPartDataHandler.cs
@@ -82,7 +82,7 @@ public async Task ProcessPartAsync(
                 partNumber, buffer.Length);
                 
             // Add the buffered part to the buffer manager
-            await _partBufferManager.AddBufferAsync(buffer, cancellationToken).ConfigureAwait(false);
+            _partBufferManager.AddBuffer(buffer);
 
             Logger.DebugFormat("BufferedPartDataHandler: [Part {0}] Added to buffer manager",
                 partNumber);
diff --git a/sdk/src/Services/S3/Custom/Transfer/Internal/IPartBufferManager.cs b/sdk/src/Services/S3/Custom/Transfer/Internal/IPartBufferManager.cs
index 004c27092eae..9675c60b321e 100644
--- a/sdk/src/Services/S3/Custom/Transfer/Internal/IPartBufferManager.cs
+++ b/sdk/src/Services/S3/Custom/Transfer/Internal/IPartBufferManager.cs
@@ -48,9 +48,7 @@ internal interface IPartBufferManager : IDisposable
         /// Adds a downloaded part buffer and signals readers when next expected part arrives.
         /// </summary>
         /// <param name="buffer">The downloaded part buffer to add.</param>
-        /// <param name="cancellationToken">A token to cancel the operation.</param>
-        /// <returns>A task that completes when the buffer has been added and signaling is complete.</returns>
-        Task AddBufferAsync(StreamPartBuffer buffer, CancellationToken cancellationToken);
+        void AddBuffer(StreamPartBuffer buffer);
         
         /// <summary>
         /// Reads data from the buffer manager. Automatically handles sequential part consumption
diff --git a/sdk/src/Services/S3/Custom/Transfer/Internal/PartBufferManager.cs b/sdk/src/Services/S3/Custom/Transfer/Internal/PartBufferManager.cs
index 57d700363eb0..c679fcb91f9e 100644
--- a/sdk/src/Services/S3/Custom/Transfer/Internal/PartBufferManager.cs
+++ b/sdk/src/Services/S3/Custom/Transfer/Internal/PartBufferManager.cs
@@ -84,7 +84,7 @@ namespace Amazon.S3.Transfer.Internal
     ///    - Example: With MaxInMemoryParts=10, if parts 5-14 are buffered, the task downloading
     ///      part 15 blocks here until the reader consumes and releases part 5's buffer
     /// 2. Read part data from S3 into pooled buffer
-    /// 3. Add buffered part: await <see cref="AddBufferAsync"/>
+    /// 3. Add buffered part: <see cref="AddBuffer"/>
     ///    - Adds buffer to _partDataSources dictionary
     ///    - Signals _partAvailable to wake consumer if waiting
     /// 4. Consumer eventually releases the buffer slot after reading the part
@@ -286,7 +286,7 @@ public void AddDataSource(IPartDataSource dataSource)
         }
 
         /// <inheritdoc/>
-        public async Task AddBufferAsync(StreamPartBuffer buffer, CancellationToken cancellationToken)
+        public void AddBuffer(StreamPartBuffer buffer)
         {
             ThrowIfDisposed();
             
diff --git a/sdk/test/Services/S3/UnitTests/Custom/BufferedPartDataHandlerTests.cs b/sdk/test/Services/S3/UnitTests/Custom/BufferedPartDataHandlerTests.cs
index 48c3e8369170..e7131cdc208d 100644
--- a/sdk/test/Services/S3/UnitTests/Custom/BufferedPartDataHandlerTests.cs
+++ b/sdk/test/Services/S3/UnitTests/Custom/BufferedPartDataHandlerTests.cs
@@ -78,7 +78,7 @@ public async Task ProcessPartAsync_BuffersPartData()
 
             // Assert - should add buffer to manager
             mockBufferManager.Verify(
-                x => x.AddBufferAsync(It.IsAny<StreamPartBuffer>(), It.IsAny<CancellationToken>()),
+                x => x.AddBuffer(It.IsAny<StreamPartBuffer>()),
                 Times.Once);
         }
 
@@ -92,9 +92,8 @@ public async Task ProcessPartAsync_ReadsExactContentLength()
 
             StreamPartBuffer capturedBuffer = null;
             var mockBufferManager = new Mock<IPartBufferManager>();
-            mockBufferManager.Setup(x => x.AddBufferAsync(It.IsAny<StreamPartBuffer>(), It.IsAny<CancellationToken>()))
-                .Callback<StreamPartBuffer, CancellationToken>((buffer, ct) => capturedBuffer = buffer)
-                .Returns(Task.CompletedTask);
+            mockBufferManager.Setup(x => x.AddBuffer(It.IsAny<StreamPartBuffer>()))
+                .Callback<StreamPartBuffer>((buffer) => capturedBuffer = buffer);
 
             var config = MultipartDownloadTestHelpers.CreateBufferedDownloadConfiguration();
             var handler = new BufferedPartDataHandler(mockBufferManager.Object, config);
@@ -124,9 +123,8 @@ public async Task ProcessPartAsync_HandlesSmallPart()
 
             StreamPartBuffer capturedBuffer = null;
             var mockBufferManager = new Mock<IPartBufferManager>();
-            mockBufferManager.Setup(x => x.AddBufferAsync(It.IsAny<StreamPartBuffer>(), It.IsAny<CancellationToken>()))
-                .Callback<StreamPartBuffer, CancellationToken>((buffer, ct) => capturedBuffer = buffer)
-                .Returns(Task.CompletedTask);
+            mockBufferManager.Setup(x => x.AddBuffer(It.IsAny<StreamPartBuffer>()))
+                .Callback<StreamPartBuffer>((buffer) => capturedBuffer = buffer);
 
             var config = MultipartDownloadTestHelpers.CreateBufferedDownloadConfiguration();
             var handler = new BufferedPartDataHandler(mockBufferManager.Object, config);
@@ -155,9 +153,8 @@ public async Task ProcessPartAsync_HandlesLargePart()
 
             StreamPartBuffer capturedBuffer = null;
             var mockBufferManager = new Mock<IPartBufferManager>();
-            mockBufferManager.Setup(x => x.AddBufferAsync(It.IsAny<StreamPartBuffer>(), It.IsAny<CancellationToken>()))
-                .Callback<StreamPartBuffer, CancellationToken>((buffer, ct) => capturedBuffer = buffer)
-                .Returns(Task.CompletedTask);
+            mockBufferManager.Setup(x => x.AddBuffer(It.IsAny<StreamPartBuffer>()))
+                .Callback<StreamPartBuffer>((buffer) => capturedBuffer = buffer);
 
             var config = MultipartDownloadTestHelpers.CreateBufferedDownloadConfiguration();
             var handler = new BufferedPartDataHandler(mockBufferManager.Object, config);
@@ -191,9 +188,8 @@ public async Task ProcessPartAsync_PreservesDataIntegrity()
 
             StreamPartBuffer capturedBuffer = null;
             var mockBufferManager = new Mock<IPartBufferManager>();
-            mockBufferManager.Setup(x => x.AddBufferAsync(It.IsAny<StreamPartBuffer>(), It.IsAny<CancellationToken>()))
-                .Callback<StreamPartBuffer, CancellationToken>((buffer, ct) => capturedBuffer = buffer)
-                .Returns(Task.CompletedTask);
+            mockBufferManager.Setup(x => x.AddBuffer(It.IsAny<StreamPartBuffer>()))
+                .Callback<StreamPartBuffer>((buffer) => capturedBuffer = buffer);
 
             var config = MultipartDownloadTestHelpers.CreateBufferedDownloadConfiguration();
             var handler = new BufferedPartDataHandler(mockBufferManager.Object, config);
@@ -234,7 +230,7 @@ public async Task ProcessPartAsync_HandlesZeroByteResponse()
 
             // Assert - should handle empty response gracefully
             mockBufferManager.Verify(
-                x => x.AddBufferAsync(It.IsAny<StreamPartBuffer>(), It.IsAny<CancellationToken>()),
+                x => x.AddBuffer(It.IsAny<StreamPartBuffer>()),
                 Times.Once);
         }
 
@@ -301,7 +297,7 @@ public async Task ProcessPartAsync_WithUnexpectedEOF_DoesNotBufferPartialData()
 
             // Assert - should NOT have added any buffer to manager since download failed
             mockBufferManager.Verify(
-                x => x.AddBufferAsync(It.IsAny<StreamPartBuffer>(), It.IsAny<CancellationToken>()),
+                x => x.AddBuffer(It.IsAny<StreamPartBuffer>()),
                 Times.Never);
         }
 
@@ -335,17 +331,14 @@ public async Task ProcessPartAsync_WithCancelledToken_ThrowsTaskCanceledExceptio
         }
 
         [TestMethod]
-        public async Task ProcessPartAsync_PassesCancellationTokenToBufferManager()
+        public async Task ProcessPartAsync_CallsAddBufferOnce()
         {
             // Arrange
             var partSize = 1024;
             var partData = new byte[partSize];
 
-            CancellationToken capturedToken = default;
             var mockBufferManager = new Mock<IPartBufferManager>();
-            mockBufferManager.Setup(x => x.AddBufferAsync(It.IsAny<StreamPartBuffer>(), It.IsAny<CancellationToken>()))
-                .Callback<StreamPartBuffer, CancellationToken>((buffer, ct) => capturedToken = ct)
-                .Returns(Task.CompletedTask);
+            mockBufferManager.Setup(x => x.AddBuffer(It.IsAny<StreamPartBuffer>()));
 
             var config = MultipartDownloadTestHelpers.CreateBufferedDownloadConfiguration();
             var handler = new BufferedPartDataHandler(mockBufferManager.Object, config);
@@ -361,8 +354,8 @@ public async Task ProcessPartAsync_PassesCancellationTokenToBufferManager()
             // Act
             await handler.ProcessPartAsync(1, response, cts.Token);
 
-            // Assert
-            Assert.AreEqual(cts.Token, capturedToken);
+            // Assert - verify AddBuffer was called exactly once
+            mockBufferManager.Verify(x => x.AddBuffer(It.IsAny<StreamPartBuffer>()), Times.Once);
         }
 
         #endregion
diff --git a/sdk/test/Services/S3/UnitTests/Custom/PartBufferManagerTests.cs b/sdk/test/Services/S3/UnitTests/Custom/PartBufferManagerTests.cs
index 72e3a11158c4..b07ddce455ac 100644
--- a/sdk/test/Services/S3/UnitTests/Custom/PartBufferManagerTests.cs
+++ b/sdk/test/Services/S3/UnitTests/Custom/PartBufferManagerTests.cs
@@ -78,7 +78,7 @@ public async Task NextExpectedPartNumber_IncrementsAfterPartComplete()
                 // Add part 1
                 byte[] testBuffer = ArrayPool<byte>.Shared.Rent(512);
                 var partBuffer = new StreamPartBuffer(1, testBuffer, 512);
-                await manager.AddBufferAsync(partBuffer, CancellationToken.None);
+                manager.AddBuffer(partBuffer);
 
                 // Read part 1 completely
                 byte[] readBuffer = new byte[512];
@@ -134,7 +134,7 @@ public async Task WaitForBufferSpaceAsync_WhenMaxPartsReached_Blocks()
                     await manager.WaitForBufferSpaceAsync(CancellationToken.None);
                     byte[] testBuffer = ArrayPool<byte>.Shared.Rent(512);
                     var partBuffer = new StreamPartBuffer(i, testBuffer, 512);
-                    await manager.AddBufferAsync(partBuffer, CancellationToken.None);
+                    manager.AddBuffer(partBuffer);
                 }
 
                 // Act - Try to wait for space (should block)
@@ -169,7 +169,7 @@ public async Task WaitForBufferSpaceAsync_AfterRelease_AllowsAccess()
                 await manager.WaitForBufferSpaceAsync(CancellationToken.None);
                 byte[] testBuffer = ArrayPool<byte>.Shared.Rent(512);
                 var partBuffer = new StreamPartBuffer(1, testBuffer, 512);
-                await manager.AddBufferAsync(partBuffer, CancellationToken.None);
+                manager.AddBuffer(partBuffer);
 
                 // Release space
                 manager.ReleaseBufferSpace();
@@ -226,10 +226,10 @@ public async Task WaitForBufferSpaceAsync_WithCancellation_ThrowsOperationCancel
 
         #endregion
 
-        #region AddBufferAsync Tests
+        #region AddBuffer Tests
 
         [TestMethod]
-        public async Task AddBufferAsync_CreatesBufferedDataSource()
+        public async Task AddBuffer_CreatesBufferedDataSource()
         {
             // Arrange
             var config = MultipartDownloadTestHelpers.CreateBufferedDownloadConfiguration();
@@ -241,7 +241,7 @@ public async Task AddBufferAsync_CreatesBufferedDataSource()
                 var partBuffer = new StreamPartBuffer(1, testBuffer, 512);
 
                 // Act
-                await manager.AddBufferAsync(partBuffer, CancellationToken.None);
+                manager.AddBuffer(partBuffer);
 
                 // Assert - Should be able to read from part 1
                 byte[] readBuffer = new byte[512];
@@ -256,7 +256,7 @@ public async Task AddBufferAsync_CreatesBufferedDataSource()
 
         [TestMethod]
         [ExpectedException(typeof(ArgumentNullException))]
-        public async Task AddBufferAsync_WithNullBuffer_ThrowsArgumentNullException()
+        public void AddBuffer_WithNullBuffer_ThrowsArgumentNullException()
         {
             // Arrange
             var config = MultipartDownloadTestHelpers.CreateBufferedDownloadConfiguration();
@@ -265,7 +265,7 @@ public async Task AddBufferAsync_WithNullBuffer_ThrowsArgumentNullException()
             try
             {
                 // Act
-                await manager.AddBufferAsync(null, CancellationToken.None);
+                manager.AddBuffer(null);
 
                 // Assert - ExpectedException
             }
@@ -276,7 +276,7 @@ public async Task AddBufferAsync_WithNullBuffer_ThrowsArgumentNullException()
         }
 
         [TestMethod]
-        public async Task AddBufferAsync_SignalsPartAvailable()
+        public async Task AddBuffer_SignalsPartAvailable()
         {
             // Arrange
             var config = MultipartDownloadTestHelpers.CreateBufferedDownloadConfiguration();
@@ -297,7 +297,7 @@ public async Task AddBufferAsync_SignalsPartAvailable()
                 // Add the part
                 byte[] testBuffer = ArrayPool<byte>.Shared.Rent(512);
                 var partBuffer = new StreamPartBuffer(1, testBuffer, 512);
-                await manager.AddBufferAsync(partBuffer, CancellationToken.None);
+                manager.AddBuffer(partBuffer);
 
                 // Assert - Read should complete
                 int bytesRead = await readTask;
@@ -411,7 +411,7 @@ public async Task ReadAsync_ReadsDataSequentially()
                 Buffer.BlockCopy(testData, 0, testBuffer, 0, 512);
                 
                 var partBuffer = new StreamPartBuffer(1, testBuffer, 512);
-                await manager.AddBufferAsync(partBuffer, CancellationToken.None);
+                manager.AddBuffer(partBuffer);
 
                 // Act
                 byte[] readBuffer = new byte[512];
@@ -439,7 +439,7 @@ public async Task ReadAsync_AdvancesNextExpectedPartNumber()
                 // Add part 1
                 byte[] testBuffer = ArrayPool<byte>.Shared.Rent(512);
                 var partBuffer = new StreamPartBuffer(1, testBuffer, 512);
-                await manager.AddBufferAsync(partBuffer, CancellationToken.None);
+                manager.AddBuffer(partBuffer);
 
                 // Read part 1 completely
                 byte[] readBuffer = new byte[512];
@@ -572,7 +572,7 @@ public async Task ReadAsync_WaitsForPartAvailability()
                 // Add the part asynchronously
                 byte[] testBuffer = ArrayPool<byte>.Shared.Rent(512);
                 var partBuffer = new StreamPartBuffer(1, testBuffer, 512);
-                await manager.AddBufferAsync(partBuffer, CancellationToken.None);
+                manager.AddBuffer(partBuffer);
 
                 // Assert - Read should complete
                 int bytesRead = await readTask;
@@ -653,14 +653,14 @@ public async Task ReadAsync_ReadingAcrossPartBoundary_FillsBuffer()
                 byte[] testBuffer1 = ArrayPool<byte>.Shared.Rent(100);
                 Buffer.BlockCopy(testData1, 0, testBuffer1, 0, 100);
                 var partBuffer1 = new StreamPartBuffer(1, testBuffer1, 100);
-                await manager.AddBufferAsync(partBuffer1, CancellationToken.None);
+                manager.AddBuffer(partBuffer1);
 
                 // Add Part 2 (100 bytes) 
                 byte[] testData2 = MultipartDownloadTestHelpers.GenerateTestData(100, 100);
                 byte[] testBuffer2 = ArrayPool<byte>.Shared.Rent(100);
                 Buffer.BlockCopy(testData2, 0, testBuffer2, 0, 100);
                 var partBuffer2 = new StreamPartBuffer(2, testBuffer2, 100);
-                await manager.AddBufferAsync(partBuffer2, CancellationToken.None);
+                manager.AddBuffer(partBuffer2);
 
                 // Act - Request 150 bytes (spans both parts)
                 byte[] readBuffer = new byte[150];
@@ -700,7 +700,7 @@ public async Task ReadAsync_MultiplePartsInSingleRead_AdvancesCorrectly()
                     byte[] testBuffer = ArrayPool<byte>.Shared.Rent(50);
                     Buffer.BlockCopy(testData, 0, testBuffer, 0, 50);
                     var partBuffer = new StreamPartBuffer(i, testBuffer, 50);
-                    await manager.AddBufferAsync(partBuffer, CancellationToken.None);
+                    manager.AddBuffer(partBuffer);
                 }
 
                 // Act - Read 150 bytes (all 3 parts)
@@ -729,7 +729,7 @@ public async Task ReadAsync_PartCompletes_AdvancesToNextPart()
                 // Add part 1
                 byte[] testBuffer1 = ArrayPool<byte>.Shared.Rent(100);
                 var partBuffer1 = new StreamPartBuffer(1, testBuffer1, 100);
-                await manager.AddBufferAsync(partBuffer1, CancellationToken.None);
+                manager.AddBuffer(partBuffer1);
 
                 // Read part 1 completely
                 byte[] readBuffer = new byte[100];
@@ -741,7 +741,7 @@ public async Task ReadAsync_PartCompletes_AdvancesToNextPart()
                 // Add part 2
                 byte[] testBuffer2 = ArrayPool<byte>.Shared.Rent(100);
                 var partBuffer2 = new StreamPartBuffer(2, testBuffer2, 100);
-                await manager.AddBufferAsync(partBuffer2, CancellationToken.None);
+                manager.AddBuffer(partBuffer2);
 
                 // Read part 2
                 int bytesRead = await manager.ReadAsync(readBuffer, 0, 100, CancellationToken.None);
@@ -768,14 +768,14 @@ public async Task ReadAsync_EmptyPart_ContinuesToNextPart()
                 // Add empty part 1
                 byte[] testBuffer1 = ArrayPool<byte>.Shared.Rent(100);
                 var partBuffer1 = new StreamPartBuffer(1, testBuffer1, 0); // 0 bytes
-                await manager.AddBufferAsync(partBuffer1, CancellationToken.None);
+                manager.AddBuffer(partBuffer1);
 
                 // Add part 2 with data
                 byte[] testData2 = MultipartDownloadTestHelpers.GenerateTestData(100, 0);
                 byte[] testBuffer2 = ArrayPool<byte>.Shared.Rent(100);
                 Buffer.BlockCopy(testData2, 0, testBuffer2, 0, 100);
                 var partBuffer2 = new StreamPartBuffer(2, testBuffer2, 100);
-                await manager.AddBufferAsync(partBuffer2, CancellationToken.None);
+                manager.AddBuffer(partBuffer2);
 
                 // Act - Try to read 100 bytes starting from part 1
                 byte[] readBuffer = new byte[100];
@@ -945,7 +945,7 @@ public void Dispose_DisposesAllDataSources()
             
             byte[] testBuffer = ArrayPool<byte>.Shared.Rent(512);
             var partBuffer = new StreamPartBuffer(1, testBuffer, 512);
-            manager.AddBufferAsync(partBuffer, CancellationToken.None).Wait();
+            manager.AddBuffer(partBuffer);
 
             // Act
             manager.Dispose();
@@ -963,7 +963,7 @@ public void Dispose_ClearsCollection()
             
             byte[] testBuffer = ArrayPool<byte>.Shared.Rent(512);
             var partBuffer = new StreamPartBuffer(1, testBuffer, 512);
-            manager.AddBufferAsync(partBuffer, CancellationToken.None).Wait();
+            manager.AddBuffer(partBuffer);
 
             // Act
             manager.Dispose();