The update is small, coming in a just 91.5MB, and is listed as build OPM1.180104.166.
Essential has been notorious for rolling out quick updates to the PH-1 ever since the device launched last year. It has received numerous camera updates, bug fixes, and new features every couple weeks. While it did take awhile for Essential to roll out Android 8.1 to the device, Essential Phone owners can probably look forward to a speedy Android P rollout once the consumer version is ready in Q3.
For the record, my unlocked Pixel 2 XL is still on the April 2018 security patch.