Delta sync is one of two features that I'd love to see added to BTSync. +1 for me. The other feature is one of a sort of global hash table where two hashes of two files that are identical wouldn't have to be transferred because that block of data is already at the destination. According to this thread, they're going to do it: Perhaps these two features are related. I'm not a developper so I don't know. What's the roadmap for proposed features? When can we expect a version 1.0 release?