Yes, the latest version of s3cmd supports Amazon S3 multipart uploads.
Multipart uploads are automatically used when a file to upload is larger than 15MB.
In that case the file is split into multiple parts, with each part of 15MB in size (the last part can be smaller). Each part is then uploaded separately and then reconstructed at destination when the transfer is completed.
With this new feature, if an upload of a part fails, it can be restarted without affecting any of the other parts already uploaded.
There are two options related to multipart uploads in s3cmd. They are:
Disable multipart uploads for all files
Size of each chunk of a multipart upload. Files bigger than SIZE are automatically uploaded as multithreaded-multipart, smaller files are uploaded using the traditional method. SIZE is in Mega-Bytes, default
chunk size is 15MB, minimum allowed chunk size is 5MB, maximum is 5GB.