Apple is now allowing developers to generate 100 app promo codes per app release, according to many developers. Before today, developers were limited to just 50 promo codes, which are usually given out to members of the press so they can review apps without having to pay for them. With the bump to 100 promo codes, that means developers can enable many more journalists to potentially write about their apps between releases.
Once the promo code limit is used up, developers still have to wait until their app is next updated to generate more codes. As always, the codes can be generated in iTunes Connect.