What changes have been made and are the sources available? The link on the catalog page still point to the 3.0 sources and contents list 3.0 hardware.
Source is here: http://devel.lulzbot.com/TAZ/Guava/
Main changes are:
- Leadscrew instead of threaded rod. and changes to Z axis to accommodate that, as well as a relocated Z endstop target.
- Modified enclosure for the computational bits, existing enclosure will work without modification.
- New fully enclosed power supply. Existing power supply will work without modification.
The leadscrew and Z axis changes are really the only ones that change machine operation from the 3.1 to the 4 variant. Should improve it somewhat.
You might also want to check out the Taz mini that is under development.