This release introduces new features including INDX tool board support, TLS networking in standalone mode, 2-slope pressure advance, easier control of multiple bed or chamber heaters, LRU cache for SD card, experimental third-order (S-curve) motion on 6HC, and a second USB communications channel.
Please read the upgrade notes at https://github.com/Duet3D/RepRapFirmware/wiki/Changelog-RRF-3.x-Beta#reprapfirmware-changes-from-363-to-370-beta1 before upgrading. In particular, note that Duet 2 and some older versions of PanelDue are no longer supported.
Users running Duet with attached Single Board Computer should upgrade from the unstable feed of the package server as usual. Users running in standalone mode can use the files here. There is no need to upgrade WiFi files if you are already using the ones from release 3.6.3.