Pretty sure Ult. Mjolnir turned out to be magical, too. Also, it'll probably be said to be less powerful than the 616 version.
He eventually got a magical hammer, but it looked just like regular Mjolnir, it wasn't the same one he originally had. Loeb did it, as I recall. The original hammer, with that shape, was tech based and he eventually got it back when he lost his powers and Stark repowered his old tech suit.
I didn't read the end of the Ultimate line, though, so they could have done another reveal I'm not aware of.