Roblox Premium

History
Premium was first confirmed on June 10, 2019, after "Premium" was added to the MembershipType enum. It was first speculated when an icon called "icon_premium-16.png" was added to the Roblox files. Later, changes to CoreScripts further increased the idea that a new membership was being added. This can also be confirmed through the content within the URL of the upgrade page  as it contains "premium" in it. Web APIs have also been updated to give the idea a new membership is being added. For example, https://www.roblox.com/mobileapi/userinfo has "IsPremium" at the end.

It was confirmed that Premium will be replacing Builders Club, when the BC overlay endpoint was modified on August 10, 2019, to always return "empty.png".

Plans
Membership plans for Roblox Premium are categorized by how much monthly Robux they provide. Compared to Builders Club, all memberships share the same name and icons rather than having distinct ones, and Robux is provided all at once after each renewal date instead of gradually each day.

Purchase Screen
The purchase screen displays a MeepCity banner with a picture of an avatar wearing the Golden Suit of Bling Squared and the Golden Top Hat of Bling Bling, also referred to as Mr. Bling Bling, from the Robux purchase page on it. Unlike the former Builders Club purchase screen, it is missing Gamecard information, Roblox Credit information and billing information.

First members
The first known users on Roblox to obtain a Premium membership (for testing purposes) include:

Trivia

 * The implementation of this membership is widely suspected to result in Builders Club bonus items such as the Builders Club Hard Hat becoming unavailable.
 * The API endpoint https://premiumfeatures.roblox.com/v1/users/1/subscriptions can be used to see whether a user has a Lifetime subscription as well as when their expiration and renewal dates are.
 * Replace the '1' with the ID of the user whose membership is desired to be checked.
 * Users who had the prototype version of this exclusive membership do not own a corresponding Roblox badge showcasing the ownership of Premium. They instead have the Outrageous Builders Club badge on their profile.
 * This could be caused by the highest level of Builders Club (OBC) being directly replaced by Premium given to these users. A badge of the membership is yet to be implemented.
 * It is speculated that the original plans for membership transfer were to cancel the user's Builders Club subscription and refund them the amount of Robux they would have if they continued with Builders Club.
 * The endpoint for this, /v1/users/buildersclubcancellation, was deleted sometime before RDC 2019 started.
 * Sending a GET request would result in the amount of Robux the user would recieve, while sending a POST request would go through with the process.
 * Unlike any other previous premium membership plan, Roblox Premium is the first membership program to have the ability to lengthen your group count from 5 to 100, no matter what tier you choose. This has been heavily positively commented on as many people believe it's a way from Roblox to better grant their users freedom on that platform.