We're getting pretty used to this dynamic with Apple; the iPhone 8 is still months away from being released, and that's assuming it even launches on schedule in September 2017; but already work is apparently underway on the following year's successor model; the iPhone 9.
According to Korean publication The Investor, the iPhone 9 will come in two size variants and BOTH will pack OLED display technology, building on the alleged design decisions for the iPhone 8 launch which will see one single OLED iPhone 8 accompanied by non-OLED iPhone 7s and iPhone 7s Plus models.
Allegedly, the iPhone 9 will come in 5.28in and 6.46in versions, presumably a regular model and a Plus model. What isn't clear is how these displays will be implemented; initially it was rumoured the iPhone 8 would feature a curved-edge OLED display similar to Samsung's Galaxy S8 design, but conflicting rumours have suggested Apple may have reverted to a flat design due to design and production difficulties, as well as flexible display shortages.
Whether the iPhone 9 would follow on from this with a flexible, curved-edge OLED display or continue to be flat remains to be seen depending on the iPhone 8 launch itself.
The Investor's report did, however, confirm that Samsung will supply Apple with the OLED panels for the iPhone 9, which is no surprise considering it's apparently the main supplier for the iPhone 8 too. Samsung reportedly predicts it will sell 180 million OLED panels to Apple for the iPhone 9, a significant increase on the 80 million panels for the iPhone 8.