During January 2025, Millem focused on enhancing reliability in the aws/aws-sdk-java-v2 repository, specifically targeting S3 upload workflows. They addressed concurrency issues by refactoring the checksum digest cache to use a thread-safe LinkedBlockingDeque, resolving checksum mismatches during parallel uploads with SHA1 and SHA256 algorithms. Millem also removed the default SessionMode for S3 Express Sessions, aligning API behavior with service defaults and simplifying client requests. Their work, implemented in Java and leveraging AWS SDK expertise, improved error handling and testing coverage. These targeted bug fixes contributed to more predictable S3 upload behavior and reduced integration issues for developers using the SDK.