It's not a security upgrade over current AOSP overall and is definitely not a port of GrapheneOS to other devices. Someone could make a partial port of GrapheneOS to other devices but this is not that.
> but includes security backports from GrapheneOS and CalyxOS
It has a small portion of the GrapheneOS features, similar to DivestOS before it. However, it's not preserving or restoring the standard security reduced by LineageOS as much as DivestOS did. DivestOS was not a strict upgrade over AOSP either.
CalyxOS isn't a hardened OS in the same space as GrapheneOS. It doesn't have similar exploit protections or privacy features. That's a misconception about it. They also haven't provided the June 2025 patches yet.
https://eylenburg.github.io/android_comparison.htm
> but surely more secure than LineageOS
This doesn't imply it's as secure as AOSP though despite having additional security features. Starting from LineageOS as the baseline and adding more problematic changes makes it much messier than it just being AOSP with added security features. Android 16 is required for full Android privacy/security patches and the current privacy/security improvements. Soon there will be Android 16 QPR1.