Nothing OS 4.0, based on Android 16, has entered Open Beta. It’s available now for Phone (3), Phone (2), Phone (2a), and Phone (2a) Plus, with Phone (3a) and (3a) Pro joining in October.
Users must first update to the latest stable release, then install an APK that enables the Nothing Beta Hub in settings to register and download the beta. As expected, bugs may occur, so it’s not recommended for primary devices. Feedback can be shared via Settings > System > Feedback.
Source: GSMArena