From the post:
Over the years, we have added a wide variety of new rules to Pathfinder First Edition, but none has been so well received as archetypes. It's no surprise that archetypes found such universal appeal. Allowing you to play a more specialized character, they let you play the character you want to play in a way that a single class often cannot support.
When the time came for us to look at archetypes for the Pathfinder Playtest, we knew that we wanted to make them a more integral part of the game, built to be an option from the very beginning. We also wanted to open them up a bit, so we could build archetypes allowing more than one class to access their features and feats, as opposed to having to recreate a concept for every applicable class with an entirely new archetype. This doesn't prevent us from creating more specific archetypes as well, but it opens up the design space further. In opening archetypes up, we realized that they might be easily abused if a player dipped into a variety of archetypes just to grab the best rules bits to make an overpowered character. It was a tough set of challenges, but fortunately for us, the answer was already built into the game.
Archetypes in the Pathfinder Playtest consist of a series of feats you can choose in place of your class feats. Every class gets its feats at roughly every other level, making them a perfect cost for archetypes. So if an archetype appeals to you—say, the pirate archetype—the only thing you need to do to gain access to it is take the appropriate dedication feat. Each dedication feat gives you some basic abilities and adds all the rest of that archetype's feats to your list of available class feats. The only catch is that you cannot take another dedication feat until after you have taken a specified number of archetype feats from the first one. So you can dip into a single archetype without too much trouble, but if you want more than one, you really have to put a fair amount of your character into the concept. For example, let's take a look at the pirate archetype.