Kernel version requirements:
- All SoCs productized in 2017 must launch with kernel 4.4 or newer.
- All other SoCs launching new Android devices running Android 8.0 must use kernel 3.18 or newer.
- Regardless of launch date, all SoCs with device launches on Android 8.0 remain subject to kernel changes required to enable Treble.
- Older Android devices released prior to Android 8.0 but that will be upgraded to Android 8.0 can continue to use their original base kernel version if desired.
Source: AOSP