From GTABOOM: “Tomorrow, the Diamond Casino & Resort opens its doors for all Grand Theft Auto Online players – provided you have enough GTA$ to burn at the tables. The Casino has been long anticipated and this major DLC will bring a motherload of content to the game, including an all-new series of promotions called the Diamond Program.
The new program will debut alongside the DLC tomorrow and have several tiers with different requirements and rewards. You’ll need to complete the requirements to hit the higher tiers by August 7th in order to be eligible for the rewards, so you better be prepared for some hard work and Diamond grinding.”
Source: N4G PC GTA Online Diamond Program – New Promotions Coming With Casino DLC