I don't see it on the Dev Team's blog. I'll check twitter later.
Its an unofficial version.
The real question is : Is it untethered or not ? ( i dont see it mentionned anywhere on redmondpie etc)
Probably tethered on the [bold] assumption that it's just a modification of what files it can accept.
Probably true. Also, why waste an untether hack on a beta?
Because it uses old limera1n bootrom based exploit that is unpatchable?