Android 6.0 Marshmallow rolled out for all the Nexus devices a couple of days back. The new Android brought many new functions to the existing Nexus devices. The newly announced Nexus 5X and Nexus 6P come with Android 6.0 Marshmallow out of the box.
There is another line of devices, The Android One series, which Google promised to keep them up to date. Google kept its promise and some Android One devices in India are receiving Android 6.0 Marshmallow update OTA. Although Google did not announce anything about anything related to updates for Android One devices recently. Not all of the Android One devices have received the update yet as it will take some time for the update to reach all devices.
It seems like India is the first company to get the update for Android One series. Other countries like Bangladesh, Pakistan ans Sri Lanka should expect the update soon. The update is around 340 MB in size. So make sure to connect your phone to Wi-Fi to download it quickly and avoid any network charges.