You've written this code before. An S3 event fires, your Lambda function wakes up, and the first thing it does is download a file to /tmp . Process it. Upload the result. Clean up /tmp so you don't run out of space. Repeat for every file, every invocation, every function in your pipeline. S3 Files changes that. You mount your S3 bucket as a local file system, and your Lambda code just uses open() . I built a set of AI code review agents that share a workspace through a mounted S3 bucket, orchestrated by a durable function, and the file access code is the most boring part of the whole project. That's the point. The /tmp Tax If you've built anything on Lambda that touches S3 data, you know the pattern. You need a file. S3 doesn't give you files. It gives you objects. So you download the object to /tmp , do your work, and upload the result back. # The old way: every Lambda developer has written this import boto3 s3 = boto3 .…