Tentei isso:

import boto3
from boto3.s3.transfer import TransferConfig, S3Transfer
path = "/temp/"
fileName = "bigFile.gz" # this happens to be a 5.9 Gig file
client = boto3.client('s3', region)
config = TransferConfig(
    multipart_threshold=4*1024, # number of bytes
    max_concurrency=10,
    num_download_attempts=10,
)
transfer = S3Transfer(client, config)
transfer.upload_file(path+fileName, 'bucket', 'key')

Resultado: arquivo de 5,9 gig no s3. Não parece conter várias partes.

eu encontreieste exemplo, maspart não está definido.

import boto3

bucket = 'bucket'
path = "/temp/"
fileName = "bigFile.gz"
key = 'key'

s3 = boto3.client('s3')

# Initiate the multipart upload and send the part(s)
mpu = s3.create_multipart_upload(Bucket=bucket, Key=key)
with open(path+fileName,'rb') as data:
    part1 = s3.upload_part(Bucket=bucket
                           , Key=key
                           , PartNumber=1
                           , UploadId=mpu['UploadId']
                           , Body=data)

# Next, we need to gather information about each part to complete
# the upload. Needed are the part number and ETag.
part_info = {
    'Parts': [
        {
            'PartNumber': 1,
            'ETag': part['ETag']
        }
    ]
}

# Now the upload works!
s3.complete_multipart_upload(Bucket=bucket
                             , Key=key
                             , UploadId=mpu['UploadId']
                             , MultipartUpload=part_info)

Pergunta: Alguém sabe como usar o upload de várias partes com o boto3?