Soon in retail !
Solo is limited scenario based. Currently, players fight the Hydra who is automated with an AI.
Seriously, I would not consider this game 1 player. It's a skirmish game that is built for 2+ players fighting against each other.
I like that they are offering the solo scenario, but it is not a core concept of the game, just an addition. I've seen these types of rules written and they often feel very tacked on (I'm looking at you AvP).
There are also solo/cooperative scenarios and campaign in the expansions, like the Compendium or the Rise of the Titans box.