This seems like kind of a weird thing to announce as a twitter reply, but he's the creative director and neither he nor Ubisoft have objected to any site posting this (including IGN) so...
Source: http://www.ign.com/articles/2014/03/07/watch-dogs-to-have-8-player-open-world-multiplayerIGN said:Watch Dogs will feature free roam multiplayer for up to eight players in its open world.
The news comes via Ubisoft creative director Jonathan Morin, who responded to a fan on Twitter asking what we should expect outside of the game's single-player offerings.