Correction at 6:30 a.m. PT March 13: The information about the Nexus 4 and 7 reflected inaccurate information on T-Mobile's web pages. A T-Mobile spokesperson says that its Nexus 4 and 7 devices have not received Android 5.1 and that the web pages have been updated to reflect this. The spokesperson added that the Android 5.1 update for the Nexus 6 phablet will begin rolling out next week. The corrected story is below.

Nicole Cozma/CNET

Owners of certain Nexus mobile devices should be on the lookout for Android 5.1.

Announced by Google on Monday, the latest flavor of the Android Lollipop operating system is already out for the Nexus 5 smartphone via T-Mobile. The carrier's page for the Nexus 5 shows the 5.1 update available as an over-the-air (OTA) installation via Wi-Fi as of Monday. The page says the update will be available via a cellular connection at a later date.

A Sprint support page says that Android 5.1 is available for the Nexus 6 phablet as of Wednesday via an OTA update. The page cautions that such updates may be released in stages, so Nexus 6 owners on Sprint may not see the update arrive for several days. A Sprint spokesman told CNET that the new flavor of Android is also rolling out OTA for Nexus 5.

What's different about Android 5.1? The latest update to Google's mobile OS fixes several issues in 5.0 and also throws in a few new features. Google's official blog on the update touts unspecified performance and stability improvements.

One feature new to Android 5.1 is tighter security for lost or stolen devices. Even if the device is reset back to factory conditions, a user will still need to sign in with the original Google account. The new security feature will be available on the Nexus 6 phablet and Nexus 9 tablet for starters but will pop up on other devices that come shipped with Android 5.1.

Another new feature lets you connect to a Wi-Fi network or Bluetooth device more easily via the Quick Settings menu. Users of phones with multiple SIM card slots will be able to switch between the cards without having to physically swap them out. And phone calls should be clearer thanks to the new high-definition voice calling available between Android 5.1 devices.

Nexus owners who don't want to wait for their carrier to roll out Android 5.1 can "flash" their devices with factory images available directly from Google. But be forewarned that this process is much more complex than simply installing the OTA update. The process also wipes your device clean, which means you lose any personal data. So if you're in no hurry, you're better off waiting for your carrier's update, even if it may take awhile.