Sony Mobile is currently seeding Android Marshmallow firmware for the Xperia M5, in the form of build number 30.2.A.0.100. This follows on from the Android 6.0.1 Marshmallow release for the Xperia M4 Aqua earlier today.
So far the latest build has only arrived on the E5603 Xperia M5 variant, but we expect it to hit all variants, including the Xperia M5 Dual shortly. We will upload the FTF firmware files shortly, but do let us know your impressions in the meantime.
Download FTF firmware for Xperia M5 – Build number 30.2.B.0.100 (Android 6.0 Marshmallow)
Thanks Abdulghani and Henry!