In listening to James Shore at #CraftConf, I'm forming the impression that FaST intends to constrain groups as little as posible, but in key ways that promote changes in habits. Specifically, strong nudges towards actual collaboration and teamwork. In that way, it reminds me an awful lot of XP.
@jbrains This makes sense. I recall @qrquartel telling me that FaST evolved from an XP team, which discovered it while trying novel things to deal with their context.