Many websites published information that Xiaomi develops new project named Chiron. It's sure that this project exists, but nobody knows from which series this phone will be.
In the past people talked about possible release of Xiaomi Mi6 Plus, but according to the newest information project was cancelled. Some people rumored that Chiron may be codename for Mi7, but this guess probably isn't correct because journalists wrote that new Xiaomi's phone will have 6-inch bezel-less display with 9:18 aspect ratio. Inside phone will have 8GB of RAM and Qualcomm Snapdragon 835 processor, so it means that under Chiron codename probably hides Xiaomi Mi Note 3 or Xiaomi Mi MIX 2, but for confirmation we have to wait until Xiaomi will release official info in this case.