Recently info on a Marshmallow update for the Sony Xperia M4 Aqua has been popping up online for some time now. Most recently, in an update schedule from Canadian carrier Rogers. It now appears the update for the M4 Aqua is already seeding to many devices internationally. The package in question has the build number 26.3.A.0.131 and is available for both the single-SIM and Dual-SIM variants of the device.
The Xperia M5 has joined the fun as well. A Marshmallow-based ROM with build number 30.2.A.0.100 has also been spotted in the wild. However, unlike its M4 counterpart, it currently seems to have a rather limited reach and is only available for some E5603 units.
On a side note, early M4 Aqua upgraders are reporting that the 6.0.1 ROM lacks the Marshmallow adoptable storage feature. We are yet to receive word if this is the case for the M5 as well, but the latter doesn’t have to deal with the realities of 8GB of onboard memory.