From CBR News
Well, it looks like it's a 616/Ultimate crossover. To be honest, it doesn't bother me. I'm definitely looking forward to seeing how this works. If I had to pick, it would be Peter coming to the Ultimate Universe, rather than Miles going to 616, but I'll be interested to see it either way.
Granted, there's also a chance this isn't 616 Peter, just like the crossover in Ultimate Fantastic Four turned out to be Zombie-Reed, not 616. Or it could be a different Miles. But I think this is going to be the real deal, if I had to guess.
Alonso on Marvel's Ultimate "Spider-men" Crossover
That confirms that it will, in fact, be 616 and Ultimate crossing over. Not much else is revealed, though, in the interest of keeping some of the story a surprise.