This beta release brings a number of new features and bug fixes. See https://github.com/Duet3D/RepRapFirmware/wiki/Changelog-RRF-3.x-Beta#reprapfirmware-350beta2 for the change list.
Users of Duets in SBC mode should update from the package server. User of Duet in standalone mode should use the files here. The WiFi files are from WiFiSocketServerRTOS release 2.1beta3.