diff --git a/.changes/next-release/bugfix-S3TransferManager-2f34394.json b/.changes/next-release/bugfix-S3TransferManager-2f34394.json
new file mode 100644
index 000000000000..c36c5269f4b2
--- /dev/null
+++ b/.changes/next-release/bugfix-S3TransferManager-2f34394.json
@@ -0,0 +1,6 @@
+{
+    "category": "S3 Transfer Manager", 
+    "contributor": "", 
+    "type": "bugfix", 
+    "description": "A couple of minor refactoring on the S3TransferManager. 1. `CompletedDirectoryUpload#failedTransfers` now returns `List<FailedFileUpload>` instead of `Collection<FailedFileUpload>`. 2. `UploadDirectoryOverrideConfiguration#uploadFileRequestTransformer` now returns `Consumer<UploadFileRequest.Builder>` instead of `Optional<Consumer<UploadFileRequest.Builder>>` it will be no-op if no uploadFileRequestTransformer is provided"
+}
diff --git a/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/CompletedDirectoryDownload.java b/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/CompletedDirectoryDownload.java
index 9784177486a0..159487059a6c 100644
--- a/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/CompletedDirectoryDownload.java
+++ b/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/CompletedDirectoryDownload.java
@@ -18,6 +18,7 @@
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.List;
 import java.util.Objects;
 import software.amazon.awssdk.annotations.SdkPreviewApi;
 import software.amazon.awssdk.annotations.SdkPublicApi;
@@ -38,15 +39,15 @@ public final class CompletedDirectoryDownload implements CompletedDirectoryTrans
                                                          ToCopyableBuilder<CompletedDirectoryDownload.Builder,
                                                              CompletedDirectoryDownload> {
 
-    private final Collection<FailedFileDownload> failedTransfers;
+    private final List<FailedFileDownload> failedTransfers;
 
     private CompletedDirectoryDownload(DefaultBuilder builder) {
-        this.failedTransfers = Collections.unmodifiableCollection(
+        this.failedTransfers = Collections.unmodifiableList(
             new ArrayList<>(Validate.paramNotNull(builder.failedTransfers, "failedTransfers")));
     }
 
     @Override
-    public Collection<FailedFileDownload> failedTransfers() {
+    public List<FailedFileDownload> failedTransfers() {
         return failedTransfers;
     }
 
diff --git a/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/CompletedDirectoryTransfer.java b/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/CompletedDirectoryTransfer.java
index f0ab9be05caf..e050fc08822c 100644
--- a/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/CompletedDirectoryTransfer.java
+++ b/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/CompletedDirectoryTransfer.java
@@ -15,7 +15,7 @@
 
 package software.amazon.awssdk.transfer.s3;
 
-import java.util.Collection;
+import java.util.List;
 import software.amazon.awssdk.annotations.SdkPreviewApi;
 import software.amazon.awssdk.annotations.SdkPublicApi;
 
@@ -34,5 +34,5 @@ public interface CompletedDirectoryTransfer extends CompletedTransfer {
      *
      * @return an immutable list of failed transfers
      */
-    Collection<? extends FailedObjectTransfer> failedTransfers();
+    List<? extends FailedObjectTransfer> failedTransfers();
 }
diff --git a/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/CompletedDirectoryUpload.java b/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/CompletedDirectoryUpload.java
index bdc8f9d27c38..7c144b8a9c7d 100644
--- a/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/CompletedDirectoryUpload.java
+++ b/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/CompletedDirectoryUpload.java
@@ -18,6 +18,7 @@
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
+import java.util.List;
 import java.util.Objects;
 import software.amazon.awssdk.annotations.SdkPreviewApi;
 import software.amazon.awssdk.annotations.SdkPublicApi;
@@ -38,15 +39,15 @@ public final class CompletedDirectoryUpload implements CompletedDirectoryTransfe
                                                        ToCopyableBuilder<CompletedDirectoryUpload.Builder,
                                                            CompletedDirectoryUpload> {
     
-    private final Collection<FailedFileUpload> failedTransfers;
+    private final List<FailedFileUpload> failedTransfers;
 
     private CompletedDirectoryUpload(DefaultBuilder builder) {
-        this.failedTransfers = Collections.unmodifiableCollection(
+        this.failedTransfers = Collections.unmodifiableList(
             new ArrayList<>(Validate.paramNotNull(builder.failedTransfers, "failedTransfers")));
     }
     
     @Override
-    public Collection<FailedFileUpload> failedTransfers() {
+    public List<FailedFileUpload> failedTransfers() {
         return failedTransfers;
     }
 
diff --git a/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/DownloadDirectoryOverrideConfiguration.java b/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/DownloadDirectoryOverrideConfiguration.java
index db9162cde6be..e6f18e8054f6 100644
--- a/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/DownloadDirectoryOverrideConfiguration.java
+++ b/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/DownloadDirectoryOverrideConfiguration.java
@@ -16,7 +16,6 @@
 package software.amazon.awssdk.transfer.s3;
 
 import java.util.Objects;
-import java.util.Optional;
 import java.util.function.Consumer;
 import software.amazon.awssdk.annotations.SdkPreviewApi;
 import software.amazon.awssdk.annotations.SdkPublicApi;
@@ -45,11 +44,11 @@ private DownloadDirectoryOverrideConfiguration(DefaultBuilder builder) {
     }
 
     /**
-     * @return the optional download request transformer
+     * @return the download request transformer if not null, otherwise no-op
      * @see DownloadDirectoryOverrideConfiguration.Builder#downloadFileRequestTransformer(Consumer)
      */
-    public Optional<Consumer<DownloadFileRequest.Builder>> downloadFileRequestTransformer() {
-        return Optional.ofNullable(downloadFileRequestTransformer);
+    public Consumer<DownloadFileRequest.Builder> downloadFileRequestTransformer() {
+        return downloadFileRequestTransformer == null ? ignore -> { } : downloadFileRequestTransformer;
     }
 
     @Override
diff --git a/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/UploadDirectoryOverrideConfiguration.java b/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/UploadDirectoryOverrideConfiguration.java
index ae3ceb3d3d23..8b5ddfcee087 100644
--- a/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/UploadDirectoryOverrideConfiguration.java
+++ b/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/UploadDirectoryOverrideConfiguration.java
@@ -75,11 +75,11 @@ public Optional<Boolean> recursive() {
     }
 
     /**
-     * @return the optional upload request transformer
+     * @return the upload request transformer if not null, otherwise no-op
      * @see UploadDirectoryOverrideConfiguration.Builder#uploadFileRequestTransformer(Consumer)
      */
-    public Optional<Consumer<UploadFileRequest.Builder>> uploadFileRequestTransformer() {
-        return Optional.ofNullable(uploadFileRequestTransformer);
+    public Consumer<UploadFileRequest.Builder> uploadFileRequestTransformer() {
+        return uploadFileRequestTransformer == null ? ignore -> { } : uploadFileRequestTransformer;
     }
 
     @Override
diff --git a/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/internal/UploadDirectoryHelper.java b/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/internal/UploadDirectoryHelper.java
index 5ece1ddf7cd6..bf19bc60e151 100644
--- a/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/internal/UploadDirectoryHelper.java
+++ b/services-custom/s3-transfer-manager/src/main/java/software/amazon/awssdk/transfer/s3/internal/UploadDirectoryHelper.java
@@ -237,7 +237,7 @@ private UploadFileRequest constructUploadRequest(UploadDirectoryRequest uploadDi
                                                                     .putObjectRequest(putObjectRequest);
 
         uploadDirectoryRequest.overrideConfiguration()
-                              .flatMap(UploadDirectoryOverrideConfiguration::uploadFileRequestTransformer)
+                              .map(UploadDirectoryOverrideConfiguration::uploadFileRequestTransformer)
                               .ifPresent(c -> c.accept(requestBuilder));
 
         return requestBuilder.build();
diff --git a/services-custom/s3-transfer-manager/src/test/java/software/amazon/awssdk/transfer/s3/DownloadDirectoryOverrideConfigurationTest.java b/services-custom/s3-transfer-manager/src/test/java/software/amazon/awssdk/transfer/s3/DownloadDirectoryOverrideConfigurationTest.java
index 9535fff74246..1c8da69ca8f4 100644
--- a/services-custom/s3-transfer-manager/src/test/java/software/amazon/awssdk/transfer/s3/DownloadDirectoryOverrideConfigurationTest.java
+++ b/services-custom/s3-transfer-manager/src/test/java/software/amazon/awssdk/transfer/s3/DownloadDirectoryOverrideConfigurationTest.java
@@ -15,32 +15,11 @@
 
 package software.amazon.awssdk.transfer.s3;
 
-
-import static org.assertj.core.api.Assertions.assertThat;
-
-import java.nio.file.Paths;
 import nl.jqno.equalsverifier.EqualsVerifier;
 import org.junit.jupiter.api.Test;
 
 class DownloadDirectoryOverrideConfigurationTest {
 
-    @Test
-    void defaultBuilder() {
-        DownloadDirectoryOverrideConfiguration configuration =
-            DownloadDirectoryOverrideConfiguration.builder()
-                                                  .build();
-        assertThat(configuration.downloadFileRequestTransformer()).isEmpty();
-    }
-
-    @Test
-    void defaultBuilderWithPropertySet() {
-        DownloadDirectoryOverrideConfiguration configuration =
-            DownloadDirectoryOverrideConfiguration.builder()
-                .downloadFileRequestTransformer((request -> request.destination(Paths.get("."))))
-                                                  .build();
-        assertThat(configuration.downloadFileRequestTransformer()).isNotEmpty();
-    }
-
     @Test
     void equalsHashCode() {
         EqualsVerifier.forClass(DownloadDirectoryOverrideConfiguration.class).verify();