Fedora has been working on transitioning to Zchunk for its DNF metadata due to its good compression ratio while being delta-friendly and leveraging the existing work of Zstandard and Zsync/casync. The metadata has been offered in Zchunk for some weeks while more client testing is needed before landing that support in Rawhide and in turn for Fedora 30…

Source: Phoronix – Fedora Still Needs Help Testing The New Zchunk Metadata Support