Lately, Google has started pushing out the Android security patch for the month of April to Pixel and Nexus devices. And now Blackberry has also started pushing out the security updates to it's Android powered devices.
Given that it's an OTA roll out so will take time to reach every unit so be patient.
If you own a BlackBerry Priv, DTEK 50 or DTEK 60 smartphones you'll soon get notification of April security patch.
By doing so Blackberry has now become the first non-google OEM to roll out this new Android security update.