After a month of Android 8.1 Oreo beta testing, Essential starts rolling out stable Android 8.1 Oreo update with March 2018 security patch to its Essential PH-1. The update is rolling out through OTA and it will take few days to complete the roll out. If you cannot wait for the OTA, you can download and flash the OTA update (OPM1.180104.092) manually.
The most important change in this update is slow-scrolling jitter fix – an issue that was plagued the device since its launch. The update also includes dynamic Calendar and Clock icons, latest Android security patch (March 2018) for enhanced security and Android 8.1 native features like Smart Text Selection, faster Startup and App Sign-in, Google Play Protect security scans and more.
Both Essential Phone PH-1 runs Android 8.1 Oreo beta and Android 7.1.1 Nougat will get the 8.1 stable build (build OPM1.180104.092) through OTA (over-the-air). For 8.1 beta users the update weighs around 276MB and for 7.1 Nougat it weighs around 1GB.
If you have not received the update notification yet, check it manually by heading to Settings > About Device > System update. If you cannot wait for the OTA you can download and flash the OTA update manually.
Essential PH-1 runs Android 8.1 Oreo beta (build OPM1.180104.010), download stable Android 8.1 OTA update (build OPM1.180104.092) from here and sideload it manually. (Source)