Google recently launched the Next Iteration of its Android Operating System Android 8.0 Oreo. The Tech Giant also pushed Android Oreo source code to AOSP, helping the developers develop custom ROMs for their devices based on Oreo.
Well, if you are a OnePlus X owner, then this recent development might be of interest to you. Developer "YumeMichi" has successfully ported Android 8.0 Oreo LineageOS 15 on the OnePlus X. Additionally, most major aspects of the phone are working as expected (such as the RIL, WiFi, sensors, etc.), but it's still not suitable for daily use.
You'll need to Unlock Bootloader and Install TWRP Custom Recovery in-order to Install the LineageOS 15 Android 8.0 Oreo Rom on OnePlus X Onyx. You can grab the Custom Rom ZIP file from below.
Download LineageOS 15 for OnePlus X Onyx
LineageOS 15 (Recent Release) (Thanks to the Developer)