The antihero rules have been updated and the last two antihero playbooks have been released. The rules can be found in the appendix section of v4.0 and the playbooks have been added to the playbook folder.
All of the antihero mechanics and options have been updated since v4.0 to fit with the discipline system. They represent a way to continue the story of your PC while changing their way of interacting with the world. Most of the playbooks introduce new mechanics, so it will be interesting to see how they play out.
Right now, the playbooks are focused more on exploring interesting dynamics than balance. Antiheroes tend to be weaker with their actions but have more powerful special abilities. I expect it will lead to needing safer play, but more dramatic moments.