S3 Transfer Manager v2 Now Generally Available

[wty-Bryant]

On January 30, 2026, we officially released feature/s3/transfermanager to production, replacing the previous feature/s3/managerutility.

What's New

The new generation Transfer Manager addresses several key issues from the previous version:

• Unified Client: Merged uploader and downloader into a single client, allowing users to transfer objects with shared configuration (concurrency, part size, etc.)
• Improved I/O Handling: Defined new I/O types replacing the old manager's S3 type usage
• Optimized Upload Strategy: Decreased memory allocation when uploading small objects (Issue Upload manager: When using io.Reader without seeking support, the uploader over allocates memory leading to high usage #2694)
• New downloader API: Added new GetObject API which returns object data in a serial io.Reader while retaining the resiliency of part/range-based downloads. See Support for io.Reader Interface in S3 Transfer Manager's Downloader #2247
• Flexible Download Options: Enabled downloading objects in parts or ranges based on configuration
• Modern Checksum Support: Deprecated ContentMD5 checksum in favor of flexible checksum options to guarantee content integrity (Issue manager.Uploader.Upload silently ignores PutObjectInput.ContentMD5 #1040)
• Batch Operations: Added directory-level operations for efficient batch transfers

Available APIs

Transfer Manager v2 implements the following public APIs:

• UploadObject: Enhanced object write support with automatic multipart upload for large objects 
• DownloadObject: Enhanced object read support with automatic multipart download for large objects 
• GetObject:  Mimics s3.GetObject API with sequential io.Reader output and concurrent multipart download 
• UploadDirectory: Enhanced directory write support with automatic concurrent file uploads for folders 
• DownloadDirectory: Enhanced bucket read support with automatic concurrent object downloads

Roadmap

Based on existing feature requests (#2095, #1463), we intend to support following functionalities in the future:

• Multipart copy object
• Key prefix delete objects

[prochac]

The GetObject is great. But could we also get something that returns io.Writer?
Similar to one in GCS SDK.
https://pkg.go.dev/cloud.google.com/go/storage#ObjectHandle.NewWriter

The UploadObject function is blocking and sucks when used for streamed (sequential) upload.

[jobstoit]

@prochac I have this project s3io that does that essentially. I had a PR here a while back too to just get it in the project here but that wasn't accepted at the time. My project does stream concurrently and yet sequential on both Read and Write, hope it helps or gives some inspiration.