MIUI 9 Global Beta ROM and China Developer ROM are rolling out for the first batch of devices.
However, Xiaomi has released MIUI 9 China Developer ROM for 13 devices. All ROMs come as Fastboot ROM.
If you want to try MIUI 9 China Developer ROM while waiting for the Global Beta ROM then you have to flash the ROM using the Fastboot method.
Note: Flash this ROM on your own risk. This Developer Beta ROM which may have unexpected bugs.