The latest update for the Cortana app on the Google Play store allows Android users to set it as their default assistant.
Setting Cortana as the default assistant allows users to access it via a long-press of the home button.
Cortana for Android allows users to access reminders, alarms, and information saved from Office 365 documents or Outlook.
Cortana currently cannot be accessed via an OS-wide voice command, and is available for Android 4.4 and up.
To set Cortana as the default assistant on Android, you will need to update the application to version 2.8.0.