The curves are similar in shape to those on the front of the iPhone 7. The new OLED screen itself is flat, while the cover glass curves into a steel frame. The design is similar conceptually to the iPhone 4 from 2010. An earlier prototype design had a thinner steel band, leaving more noticeable curved glass on the sides.
Bloomberg also says that an ambitious prototype was in testing with more dramatic curves on the top and bottom of the rear glass, similar to the original iPhone. Suppliers struggled to reliably produce the heavily curved glass so Apple is more likely to ship the design with more subdued curves.
A simpler design with an aluminum back and slightly larger dimensions is allegedly being tested.
Bloomberg also reiterates many of the rumors we've been reporting including the release of three new iPhones, a possible delay in the release of the iPhone 8, OLED display, difficulties in integrating the Touch ID sensor into the display, vertical orientation for dual rear cameras, and augmented reality features.
Apple isn't expected to unveil its new iPhones until this fall. Please follow iClarified on Twitter, Facebook, Google+, or RSS for updates.