If you have a Nexus 5 you should start hitting that Update button as the Android 5.1 OTA is rolling out in stages starting today. T Mobile and Sprint have already shared the news with their customers.
T Mobile is giving out the LRX22C version and the official changelog includes Software stability and miscellaneous Android updates.
Some bugs from 5.0 are being fixed and the battery life is improved for phones and tablets that you usually pair with Android Wear devices. International unlocked models will be receiving the update as well, so stay tuned and wait for the rollout to reach your Nexus 5.
Source: T Mobile