Most of what's needed for this has been in the main/Satoshi client since 2012. The client uses the pruned chain for most transactions because it's faster, and just uses the full blockchain for syncing with other clients. But I don't know of any clients that turn off the full-blockchain part and use only the pruned one. https://bitcointalk.org/index.php?topic=119525.0 https://bitcointalk.org/index.php?topic=118660.msg1285690#ms...