Sony has finally begun rolling Android Marshmallow update to its Xperia C4 and C4 Dual smartphones. Both phones were launched running Android 5.0 Lollipop and are just now receiving Marshmallow updates while the rest of the world is looking towards Nougat.
The company generally is fast with updates on its flagship devices, however with Marshmallow they have been quite lazy. Given that both the C4 devices run on MediaTek chipsets could be one of the reasons for delay to the new OS.
The Xperia C4 (E5503, E5306) gets an updated build number of 27.3.A.0.122 while the C4 Dual (E5333, E5343) will come with 27.3.B.0.122. You will get Sony's minimalist take on a skin over stock Android Marshmallow with Doze Mode, Now on Tap and App permissions apart from the usual assortment of security and performance enhancements.