Several days ago, The LG LS991,which is expected to be the Sprint version of the LG G4, has been spotted in a UA profile on Sprint Official website.
The Sprint’s LG G4 LS991 was spotted again in one updated UA Profile.
Sprint has made a few revisions to its User Agent profile listing for the LG LS991. As you can see from below screen shot, The LG LS991 runs Android 5.1 and the software number is LS991ZV1.
Moreover, Another LG G4 variant (Model:LG-H818)running on Android 5.1 build LMY29F has been spotted on HTML5TEST website.
The upcoming LG G4 should come with Android 5.1 out of the Box.