Considering the amount of people who have asked us if their cases will be compatible with the new phones, it's worth underscoring that Apple's own case lineup for the iPhone 6 and iPhone 6 Plus will indeed fit the new iPhone 6s and iPhone 6s Plus, and vice versa.
As iDownloadBlog reader Adam Baligian observed on Twitter, Apple's own iPhone 6s Accessories webpage states that existing cases “fit snugly and your iPhone 6s or iPhone 6 still feels incredibly slim,” even with the case on.