Google posted Android 5.1.1 Lollipop factory images for LG Nexus 4, LG Nexus 5, and the LTE variant of HTC Nexus 9. The latter is also getting the new firmware over-the-air.
As its version number suggests, Android 5.1.1 fixes some of the minor niggles in Android 5.1. It contains mostly under the hood performance and stability improvements.
For those who aren’t in the know, OTAs are usually meant for everyone, while factory images are targeted at Android developers and enthusiasts as they to be applied manually.