Mark I/II: www.fractalaudio.com/downloads/firmware-presets/axe-fx-2/16.0/axefx2_16p00beta1.zip
XL: www.fractalaudio.com/downloads/firmware-presets/axe-fx-2/16.0/axefx2_xl_16p00beta1.zip
Note that the official Version 16.00 will have much more but those things being worked on aren't ready yet. We felt that these improvements were something that shouldn't be kept from the users in the interim.
EDIT: Official Version 16.00 is now released.
XL: www.fractalaudio.com/downloads/firmware-presets/axe-fx-2/16.0/axefx2_xl_16p00beta1.zip
Note that the official Version 16.00 will have much more but those things being worked on aren't ready yet. We felt that these improvements were something that shouldn't be kept from the users in the interim.
EDIT: Official Version 16.00 is now released.