Mythology is now in Private Beta. I just passed 200 rep on that site and my profile which had been tracking Access Review Queues (350 Rep) since I started (on 101 rep with the Association Bonus) suddenly reported that I had earned Reduce Ads.
If I look at the privileges page for the private beta the Reduce Ads privilege is not displayed there, which makes sense since Private Betas don't have adverts.
It seems like Reduce Ads is almost completely hidden, it isn't displayed as a privilege to track but but the awarding point in the new Privileges Page has that check missing.
I assume this applies to any Private Beta once you cross 200 Rep.