Nexus 5 System Update

[peterx]

My phone is LG Nexus 5 with the latest Android 5.1.1 – Build Number LMY48B.

Today I checked System Update which said:

"This software update will upgrade your Nexus 5 to improve stability, increase security,...

Update size: 10.1MB

RESTART & INSTALL".

Why there is a software update for when my LG Nexus 5 is running with the latest Android 5.1.1 – Build Number LMY48B?

[xray]

Might be Marshmallow but I thought that wasn't going to be released until the end of the month. 

[JayLaw1]

Nexus phones get updates from Google, not the carrier (Telus). Google has announced monthly security updates for Nexus phones. That's all that is.