TL;DR of that change is that they've moved from a truncated SHA1 hash to SHA3/ed25519/curve25519. For more detail, here's their own summary from the technical

TL;DR of that change is that they've moved from a truncated SHA1 hash to SHA3/ed25519/curve25519. For more detail, here's their own summary from the technical specification: Here is a list of improvements of this proposal over the legacy hidden services: a) Better crypto (replaced SHA1/DH/RSA1024 with SHA3/ed25519/curve25519) b) Improved directory protocol leaking less to directory servers. c) Improved directory protocol with smaller surface for targeted attacks. d) Better onion address security against impersonation. e) More extensible introduction/rendezvous protocol. f) Offline keys for onion services g) Advanced client authorization