V6.3-000 brings significant enhancements to GT.M's use of encryption. One defensive technique is to reduce the "surface" available to an attacker. V6.3-000 reduces the surface in several ways.
The release bring numerous smaller enhancements, including to the $ZQGBLMOD() function, better handling of split $PRINCIPAL, more helpful TPRESTART messages, and more.
V6.2-001 brings important enhancements to GT.M, most notable of which is a production grade implementation of auto-relink.