This is quite clearly covered in the actual document! > For longer documents, Hashify splits the contents into as many as 15 chunks. The chunks are then Base64

This is quite clearly covered in the actual document! > For longer documents, Hashify splits the contents into as many as 15 chunks. The chunks are then Base64-encoded and sent to bit.ly in a single request. The bit.ly hashes contained in the response are then "packed" into a URL such as http://hashify.me/unpack:gYi2Ie,g4fpte http://hashify.me/unpack:gYi2Ie,g4fpte. Finally, this URL is itself shortened.