The Economist (sorry, no bylines) states that China “is deploying six road-mobile, solid-fueled (which means quick to launch) intercontinental DF-31s …”
The Economist does not provide a citation, but six is an interesting number. (I don’t think it is from IISS, which has recently said eight—although perhaps the most recent edition has revised the estimate.)
Given the 3-3 system that that the Second Artillery uses from some launch units—“a missile brigade has three subordinate launch battalions, each of which has three subordinate launch companies …”—we would expect China to add missiles in sets of nine. For more on the structure of the PLA, I recommend the source of my description of the Second Artillery 3-3 system. Kenneth Allen and Maryanne Kivlehan-Wise, Implementing PLA Second Artillery Doctrinal Reforms.
I wonder if the DF-31 deployment process will look like the DF-21 process, where the first units went into the field in the early 1990s, but testing continued and deployments did not pick up speed until several years later.