The issue with Android and its rollout technically happened about four months ago, but very few actual Android devices have it.  Sure, Google was able to bring Android M (also known as Marshmallow or Version 6.0) to the Nexus series, but it has been slow to come to other companies like HTC, Motorola, LG, Samsung, and very slow to come to Sony.  This is what is currently known about the Android M 6.0 Marshmallow Upgrade Release Date for Sony Z5, Z5 Compact, Z5 Premium, Z4, and Z3 series for carriers like Verizon, Sprint, T-Mobile, AT&T, and US Cellular. 

A recent report from Neurogadget has shown that a beta test that Sony has been running on the Z3 Series has proven an 80 percent success.  Since this process looks good, the chances of the Android Marshmallow update coming to both the Z3 and the Z3 Compact within the next few days are pretty good. 

It is quite strange that the Z3 and Z3 Compact might receive Android 6.0 first among the members of the Xperia series, as the Z3 was Sony's flagship from two years ago.  Android rollouts will go to the newest flagships first, and then trickle down to all of the others.  Clearly, the Z3 is currently more popular than the Z5 series, which includes the Z5, Z5 Compact, and Z5 Premium.  

Android Pit reports that the Wi-Fi Alliance has certified the Xperia Z5 and Z4 Marshmallow updates, and it speculates a February release date for these particular devices, but it believes that release date is a little bit optimistic.

Tech Radar reports that a Twitter tipster @Ricciolo should get the update in January, with the older models to follow shortly.  There isn't much of January left, so unless the update arrives over the weekend, it doesn't seem likely that this tipster's info is valid.  Again, it seems a little too optimistic.

The truth is that Sony hasn't even given any indicators on when this will be coming to their devices, and they have been kind of slow in the past.  Leaks about this news are also pretty scarce, but we do know this: in addition to the Z5 and Z3 series (not to mention the Z4), here is a list of other Sony devices that are set to receive the update, according to Pocket Lint. 

• Xperia Z3+
• Xperia Z3 Tablet Compact
• Xperia Z2
• Xperia Z2 Tablet
• Xperia M5
• Xperia C5 Ultra
• Xperia M4 Aqua
• Xperia C4

Assuming that the rollouts for the Z5 and Z3 Xperia series to come soon, there still might be a delay due to the carrier, like US Cellular, AT&T, Sprint, Verizon, or T-Mobile.  Certain carriers have been known to receive the Android update before others, and there isn't really a pattern. 

For those that have Sony devices, check your "Settings" to see if any updates are available, as well as "System Update" to see if you can get an over the air (OTA) update.  Perhaps optimism might be correct in this instance.