[Crisis 541]

Battle suits are the Tau Empires greatest asset and have had many thousands of hours testing, designing, and creating. So far we know of three different makes of the suits they go as follows

XV 15
XV 25
XV 8/88

My reasining is that the classes of 1-5 use physical agumentation giving the wearer a robotic exoskeleton

Classes 6-9 replace physical abilities, like mini-dreadnaughts.

The next number is the classification of the suit
2 experimental
5 stealth capabilities
8 heavy weapons

These are all my ideas and are taken and extrapolated from the avalible fluff.

[GeekyGator]

Seems right. GW had an article on this I think... not sure/too lazy to find it tho.

[orion549]

The first numbers indicate the weight class. I would expect there to only be 1-8, as Tau seem to only use an base-8 number system. Maybe a class 10 suit (Eq. to our 9) but I wouldn't take it that far yet. Weight class 3-7 would be progressively larger and heavier, in the same basic relation as the differences between the XV-1 and XV-2 class.

The second number indicates something about the suit, it seems a secondary system would be the indicator. So anything with a 5 would have a Stealth Field as it's second system, anything with a 4 a markerlight, a 1 is a SMS system, and 8 being either the Railguns or the generators associated with it.