The latest jailbreakable version of iOS at the time of this writing is iOS 12.1.2, but that could change in the very future.
iOS hobbyist @NedWilliamson Tweeted a teaser Friday afternoon of what appears to be a successful tfp0 exploit for iOS 12.2 on an iPhone 6s Plus, a feat that was purportedly made possible after working closely with long-respected security researcher Brandon Azad: