According to T-Mobile, the Android 5.1 update is scheduled to begin rolling out to the Nexus 5, Nexus 4, and Nexus 7 (2013) as early as today under build LMY47D. T-Mobile’s support pages don’t talk through a list of features or changes, but Google basically gave us one already.
Nexus 5 owners should be expecting an update that weighs in at around 222MB. The Nexus 7’s update drops in at around 202MB. Finally, the Nexus 4 update seems a bit small at just 16.7MB.
If you start seeing any of these updates, be sure to let us know! Also, be sure to grab the OTA .zip file URL with this guide.