Google Officially announced Android 5.1 Lollipop today, which brings along new features like HD Voice calling on compatible devices, dual SIM support for compatible devices, and Device Protection which essentially keeps your device locked if lost or stolen until the device receives a login from your Gmail account, which persists even after a factory data reset. Although this official roll out was stated by Google to begin today, it would have been reasonable to assume that it would potentially be limited to just the Nexus 6 and the Nexus 9, at least initially.
According to T-Mobile though this isn't the case, as they've stated that software updates to Android 5.1 Lollipop are scheduled to happen as early as today for three other devices, which includes the Nexus 4, the Nexus 5, and the Nexus 7 2013. Since this is coming from T-Mobile, we can only assume that the Nexus 7 2013 being referred to is the LTE model that was sold through their network, which makes sense, given that there would be no reason for them to post any information about the update coming to the WiFi only model. The build for the software on all three of these devices is being listed as LMY47D. It's also worth noting that T-Mobile states this is only available via over-the-air and pull down via WiFi only at this time.
They further explain that the update will be coming as an OTA via the cellular network at a later date, which means if users want to get these updates to the listed devices here, they'll have to be connected to a WiFi network to do it. All this means is that you can't download the software package when you're connected to the T-Mobile network for data. This shouldn't be a big issue for users as the Lollipop update is listed as being 222MB in size. While this isn't a large amount of data to be downloaded for some users, others may only have a small amount of data to use each month, and saving precious 4G data where you can is a good idea. T-Mobile lists specific requirements for having this update come through, which includes 222MB of free space on the device, a data connection, at least 50% battery life and the device already has to be on the Android Lollipop build LRX22c. The requirement for LRX22C is for the Nexus 4 and the Nexus 5 only while the Nexus 7 2013 must meet the other three before having the update show up as available.