Due to issues in compatibility with Voice Search on Android, Microsoft is killing the "Hey Cortana" hands-free feature on Android in the US.
Based on user-feedback, the hands-free Cortana feature was conflicting with the default voice search feature on Android, therefore Microsoft has disabled it, till they can figure out what's wrong.
The new update also adds better call and text messaging features alongwith improved performance and overall stability. You can download Cortana for Android from the Play Store link below.
Download (Play Store): Cortana
