Block or full file sync?

Does Cryptomator encrypt/modify a file block, only at the block level, so only a small block is needed to be transferred to the cloud? Or will the full file need to be transferred to the cloud?

For example, if I have a 10 MB text file, change one letter, will the full 10 MB need to be uploaded, or just the small block that was changed?

On a file basis the complete file is needed.