Xiaomi has released Android 6.0 Marshmallow based stable ROM for the Mi 3/Mi 4 in China. MIUI v7.2.8.0.MXDCNDB is available in China which means that you won't get Google Play Services pre-installed.
Therefore, we would recommend waiting for the global stable ROM to be available. This is a stable ROM though and if you can live without Google apps, give it a try.
Source: MIUI Forum
