There may have been a bit of a false start recently, when a Sprint employee took to the community forums to announce that the rollout of Jelly Bean for the Nexus S had begun. Maybe the rep confused the Nexus S for the Galaxy Nexus, as we hadn't heard any reports that users had received the OTA for the older of the two Nexii. Today, though, Sprint has posted in its forums details on the upgrade, including a release date of today, September 11th.
As previously reported, the build number will be JRO03R. The rollout should be beginning today. While we didn't have reason to doubt the veracity of the Sprint rep from a few days ago, this is even more solid info.