There has been no AT3 jailbreak and would be suspicious of anyone who claims they have (because there's been plenty of scams).
FireCore hasn't got a jailbreak for the ATV3 and pretty much never will. From what I recall they even refunded purchases after it became clear they couldn't deploy on the ATV3 so I wouldnt hold much hope. In part it's the reason that the ATV2 is selling at a premium (over the 3) on eBay etc.