Google has announced that they are release a software update today and the update will include the March Android security update.
The news of the software update for the Google Nexus 5X was announced on Reddit, you can see some details below on what is included in the update.
I know there has been some discussion here about the 5X-specific factory images that were posted yesterday on the developers site. I wanted to give some clarification around this, and specifically let you all know that an OTA update will begin rolling out today for the Nexus 5X. We have listened to your feedback, and this update includes a number of bug fixes that will improve overall stability, connectivity, and performance on the Nexus 5X. The March security update will be included with this OTA for the Nexus 5X.
As yet there are no details on exactly when the update will land, it should be available some time today as an over the air update.