1-bit SGD and insanely high minibatch sizes (8192) it would appear: which drastically reduces communication costs, making data-parallel computation scale.

If so, while very cool, that's not a general solution. Scaling batch sizes of 256 or lower would be the breakthrough. I suspect they get away with this because speech recognition has very sparse output targets (words/phonemes).

Too bad the code below isn't open-source because they got g2 instances with ~2.5 Gb/s interconnect to scale:

http://www.nikkostrom.com/publications/interspeech2015/strom...