The header only download is a client side thing and can be done already (with a client that supports it). The Unused Output Tree (UOT) - the second thing you me

The header only download is a client side thing and can be done already (with a client that supports it). The Unused Output Tree (UOT) - the second thing you mentioned - needs amendment to the blockchain (adding checkpoints). https://en.bitcoin.it/wiki/Thin_Client_Security#Header-Only_Clients https://en.bitcoin.it/wiki/Thin_Client_Security#Header-Only_...