Google has started pushing out the Android security patch for the month of April to Pixel and Nexus devices. Factory images are now available on Google's website, you can head over to the links provided below and see if your device makes an appearance.
Here's the list of the devices for which this new security patch is available:
Pixel XL (NOF27D)
Nexus 6P (N4F26U)
Nexus 5X (N4F26U)
Nexus 6 (N6F26Y)
Nexus 9 (N4F26X)
OTA files are also available for download, you can also flash piece of build by downloading the image of update.