Don't Expect a Fast iOS 12 Jailbreak
Jailbreak developers have reportedly jailbroken iOS 12, but that doesn't mean we'll see a release for the official version of iOS 12 right away.
It usually takes jailbreak developers several weeks to push a jailbreak tool to the general public. And those releases often come without warning.
At this point we aren't expecting a public jailbreak for iOS 12 beta and we'd be shocked if developers released a tool to the public on the initial iOS 12 release date.
Keep an eye out for new developments, but if you want to jailbreak iOS 12 be prepared to wait.