Apple has unveiled their latest and greatest iOS 12 on WWDC 2018, iOS 12 comes with lots of improvements as compared to earlier iOS versions. Apple claim iOS 12 to be 40% faster when it comes to opening an applications than iOS 11.
There is no jailbreak currently available for iOS 12 Betas.
This page will be updated once iOS 12 Jailbreak comes alive. Sileo for iOS 11 and 12 will be available soon. Coolstar has send copies of Sileo to developers for testing the package manager. Cydia may be not available for iOS 12 because Saurik has not updated Cydia from long time. Sileo will be open-sourced for all the Jailbreak Developers once it get released for public.