Interestingly enough, the 1.5 GB for OnePlus 5T started showing up on Tuesday for some customers but only if they chose to have the full updates. There is a magical app called Oxygen Updater that tells you when a new update is available but this is not available as partial download, only as a full update.

System

• Updated Android security patch to 2018.8
• Confirm PIN without tapping ? to unlock the phone (Settings -> Security & lock screen -> Screen lock -> PIN)

Officially there is no mention that Project Treble is supported on this ROM but the Treble Check application immediately recognizes that the OnePlus 5 with 5.1.5 ROM is Treble compatible. Android 9 will get faster on both OnePlus 6, OnePlus 5T and a year-old OnePlus 5, hopefully rather soon.

Android 9 is currently only available on Pixel devices as well as Essential (One and only) phones with the big hope that it might started showing up for other Project Treble supporting phones, including OnePlus.

Google announced that Sony Xperia XZ2, Xiaomi Mi Mix 2S, Nokia 7 Plus, Oppo R15 Pro, Vivo X21, OnePlus 6 and Essential PH?1 will be getting the update soon but there is no date when.