Note that version 8.5.1 is the first released version of GX Developer for Geosoft version 8.5 applications. Documentation: GX Developer 8.5
See http://docs.geosoft.com/gxdev/8.5/dotnet/GXNet/html/version-history.htm for a list of new API methods added in 8.5.0. Note that 8.5.1 is a maintenance release that has no new API methods. Notable in the 8.5 is the DBREAD class, which support blocked reading and writing for very large lines.
Geosoft ID authentication improvements. These important changes support user security and future rights management through Geosoft ID. Note that in the next major release of Geosoft platforms the Geosoft license key will be replaced by rights managed using Geosoft ID. This removes the need for users to park license keys to transfer rights.