Android 5.1 (Lollipop MR1)

http://officialandroid.blogspot.tw/2015/03/android-51-unwrapping-new-lollipop.html
http://www.cnet.com/news/android-5-1-reportedly-spotted-on-new-phones/
https://android.googlesource.com/platform/manifest/+/refs/heads/android-5.0.2_r1..refs/heads/android-5.1.0_r1/

Features:

• multiple SIM cards, 
• Device Protection
• high definition (HD) voice (aka. VoLTE)

Bug fixed:

• Silent mode added after missing on Android 5.0
• General improvements in system stability
• Improved RAM management
• Fixes for sudden app closures
• Improved battery management
• Excessive consumption of network devices when used Wi-Fi fixed
• Issues with wireless connections fixed
• Problems with Okay Google function solved
• Notifications problems solved
• Some sound problems experience by certain devices fixed
• Other improvements and changes
• Changes in the Material Design color palette (after users complaints, possibly for a higher version though)

[Note] git log --oneline --decorate android-5.1.0_r1..android-5.0.2_r1