CYA Bottom bracket
As you would imagine this results in a great power transfer with minimal flex but there is another reason for this. There is a wealth of bottom bracket sizes available including BB30, BB90, press fit, BB92 and doubtless somebody somewhere is working on a new one. Rather than pick a standard which may become obsolete, Niner has developed adapter inserts called the CYA. You press these into the frame using a standard headset press. You then simply install your chosen BB, essentially future proofing your bike and allowing you to adopt a different standard in the future if you so choose.
29er technology is continually adapting, not only in terms of bottom brackets but also with things like gear ratios and you may well want to change your cranks to another manufacturer in the future should they adopt a certain BB style. True, there is a small weight penalty. Niner could have made the bike lighter in a few ways but has opted for ingenuity over weight savings, and I actually prefer it this way.
One of the big advantages of this type of bottom brackets, though, is for singlespeeders. Niner has developed a single speed bottom bracket insert called an eccentric bottom bracket (or EBB) which allows you to rotate the bottom bracket within the shell in an off centre rotation to put tension on the chain, removing the need for rearward facing drop outs or a chain tensioner. This allows a no compromise transfer between a geared and single speed bike. It works too, the 2010 Single Speed World Champion rode to victory on an Air 9 Carbon.