On April 7, 2026, AWS launched S3 Files - a managed NFS v4.1/4.2 layer built on Amazon EFS that provides file-system semantics on top of S3, including read-after-write consistency, advisory file locking, and POSIX permissions. (AWS Storage Gateway's File Gateway has offered NFS-over-S3 for years, but as a caching gateway appliance, not a native file system with these guarantees.) You can mount S3 Files from EC2, Lambda, EKS, and ECS (Fargate and ECS Managed Instances launch types; EC2 launch type is not yet supported). Your code reads and writes files with open() , os.rename() , and os.listdir() . No boto3 for the data path. No /tmp juggling. No copy-then-delete to simulate a rename. In this post, I'll build two identical document-processing Lambda functions - one using the traditional S3 API approach and one using S3 Files - deploy them with Terraform, and benchmark the difference. The Long Road to a Real S3 File System For nearly two decades, developers have been trying to use S3 as a file system.…