I just applied SP1 to Studio (available from www.atmel.no/beta_ware ). The change history states:
The following new parts have been added to AVR Studio since 4.15:
- ATxmega16D4, ATxmega32D4, ATxmega64D3, ATxmega128D3, ATxmega256D3
Check the device matrix to see which devices are supported by which tools: See a list of all supported devices and tools here.
AVR ISP mkII command line SW support for XMEGA device family
9473: Programming window - Empty Flash's .hex file read-back after programming and verification
9510: Cannot program a bootloader
7966: ATmega329P signature wrong.
9291: Misguidance in AVR Studio Help-->AVR Studio User Guide-->Getting Started-- >Debugging external code projects
9545: Bug in partdescription file of ATmega640
9505 ATmega640 needs STK600 support
9509 The include file for ATxmega128A1 contains errors
9528 Wrong fuse description in ATtiny48/88
9508 I am not asked if I want to reload project even if it has changed
Perhaps the most significant of those being that bootloaders can now be programmed once again.