With few exceptions, Apple doesn't talk about the amount of RAM included in its iPhones and iPads. Even though it has an obvious impact on developers and the user experience, that information is almost always discovered after the fact by users and reviewers.
Adobe may have just leaked the amount of memory included in the new iPad Pro, though. In a post about the apps the company showed off onstage yesterday, Adobe claimed that "iPad Pro is great for creative workflows with a high res 12.9-inch touch screen display at 2732 x 2048 pixels, A9X chip, and 4GB RAM." The reference to both the A9X chip and the 4GB of RAM have since been deleted, but the reference has been preserved by ZDnet.
Apple says the A9X has roughly 1.8 times better CPU performance than the A8X and double the GPU performance of the A8X.