Stable installers were historically released as both small (web) and full (offline) versions. The offline installer is preferred for reliability. AVR Studio 5.1 Full Installer Readme (Official) . Key Features of Version 5.1 AVR® and SAM MCU Downloads Archive

If you are referring to the deep debugging protocol (used on devices like the AVR32), you need the AVR32 Software Framework.

Search for the specific installer filename: as5installer-5.1.208.exe .