Mi 4 was launched back in 2014 with 4.4.3 Kitkat Os out of the box . The Smartphone also received 5.1.1 in 2015 and Now Mi 4 is ready for Marshmallow update .
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The update is of 100+ MB and will update Mi 4 directly to Marshmallow Android 6.0.1 . The Build Number is MMB29M .