A new update for Google's Nexus devices is pushing out to T-Mobile models today. The update is LMY48M (for most of the devices) and hasn't been made available as factory image downloads by Google just yet. We expect that to happen shortly.
In the mean-time, T-Mo has included these links for folks who want to get it manually:
If you aren't on T-Mobile, you may want to wait and get the factory images from Google, once they put them up on their download servers.