Cloudflare R2 also has a tool in beta that provides an incremental migration from S3. As users request files using your R2 URLs, Cloudflare automatically migrates the files from S3 to R2 on request. Depending on your user's request patterns this may be a way to migrate everything without paying any additional cost. If you have a lot of files that are rarely accessed then they will be slow to migrate, but because they are rarely accessed your S3 costs could be significantly reduced by using different storage classes anyway. Eventually you will have a small enough number of infrequently accessed files remaining in S3 that the additional cost to migrate them all in one go can make financial sense.