There are currently two premium products - 30-day search, and full-archive search. Both of these provide access to features (search operators, complexity, and history) that have never been available before in the standard level of the API. Both of these have a period length of 30 days, within which your requests are quota’d depending on the level of your subscription.
There is no premium API that increases access to the followers or friends endpoints and currently no plans to offer this - check the roadmap for what is in progress.