Nexus 6
Google has released Android 5.1 Lollipop update for Nexus 6. XDA

Google's latest Android Lollipop treatment has made its sixth generation Nexus smartphone faster and smoother.

Recognised XDA developer, Francisco Franco announced this and said the Android 5.1 update (build LMY47D) bundles improvements in terms of ART and lots of code cleaning and optimisations on the framework for the Nexus 6. Another significant improvement is that the update now makes the quad-core Snapdragon 805 processor (2.7GHz) of Nexus 6 run on all four cores all the time.

".....the device is now running full quad-core mode all the time which helps tremendously because the Kernel task scheduler can distribute the workload through all these cores so you'll get the perception that the device is not hanging anymore," explains Francisco.

As for battery life, Google has disabled the built-in thread migration boost routines that make the battery run longer.

"It (the built-in thread migration boost routines) is a driver made by Qualcomm that receives a notifier from the task scheduler when one thread migrated from one cpu core to another and to minimise perceived lag it boosted the destination core to the same or, greeted, frequency than the origin core."

In simple words, the feature kicks in whenever one task has to be migrated from its current CPU core. In such instances, the task scheduler would tell the destination core to match or exceed the current frequency of the origin core, while lowering the perceived lag.

As these migrations occur dozens of times per second, disabling them could conserve battery life, notes the developer. According to him the Nexus 6 users on 100% stock would be surprised to see the improved battery life.

[Source: Google+ via PhoneArena]