A small OTA update looks to be headed out to the Nexus 4 today, courtesy of an update document posted on T-Mobile's support page for the device. The build number is JWR66Y, which is obviously a very, very incremental bump from the previous build JWR66V. And the changelog matches up with such an assessment, as it includes but one item: "Security." That's nice and specific.
We have to assume this update will be headed to all Play Store Nexus 4 devices as well, not merely T-Mobile's, as the two are actually one and the same.