I've had this game since before Early Access. I was in the early beta before that. Now I can't opt into the beta which is referred to on the main Longbow Website. There's no option for that in my Steam account.

EDIT: Wish I could remove this useless post disregard: You need to add the password HegemonyRome into the Beta password field in Steam. I mixed things up with the Paradox games that don't need passwords, but you just click the pull down menu and selec the beta from there...