This was first noticed by @Evleaks and then picked up by some XDA users, who were able to confirm through a Sprint employee that the nation’s third largest carrier was shipping these special handsets as the standard option.
The Sprint version has Harman/Kardon speakers in it whereas the other versions do not. They were waiting to announce this for all of the patents and agreements with JBL and Harman/Kardon to pass.
It’s the same M8 that is already available. They haven’t been marketing it as such yet due to a delay in the legal realm trying to get agreements pushed through. Soon they will be adjusting their marketing to include that the Sprint version exclusively offers Harman/Kardon technology in their BoomSound setup.
Apparently, Sprint hasn’t made an official announcement yet because it is still waiting for an agreement with Harman Kardon to be completed.
Update: And just like that, Sprint makes the official announcement.
Sweet!
[xda-developers via Cult of Android]