A benchmark listing of a Polaris 12 based video card showed up in the database of CompuBench. This is believed to be the only new GPU in the upcoming AMD Radeon RX 500 series, as all other models will be rebrands of the Radeon RX 400 series.
VideoCardz speculates the Polaris 12 chip may be used by the low-end Radeon RX 550 series. The benchmark listing shows this chip has 10 compute units and a total of 640 stream processors. It also reveals 4GB memory and a frequency of 1302MHz, which may be the Boost clockspeed.