Todesco is best known for releasing the yalu jailbreak of iOS 10.2. He confirmed the jailbreak of the iPhone XS Max on iOS 12 via Twitter.
since I’m finally done hacking the Xs Max I started using it as my daily driver and I gotta say it’s a damn fine piece of hardware
When asked for clarification, he replied:
I have jailbroken the A12, and yes, I’m running stock now.
Todesco isn't the first person to jailbreak the A12. Pangu successfully jailbroke the chip last month; however, it appears they did that on the iPhone XS.
At this point there's no indication that PanguTeam or Todesco plan to release their jailbreak to the public but you can follow iClarified on Twitter, Facebook, Google+, or RSS for updates.