I followed the tall guy's link to the AT&T forums and came across this:
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A user posted the question "When will the Marshmallow Update arrive for the S6Active?"
Here is the response:
Thank you for reaching out to the AT&T Community Forums!
That is the highly asked question these days. We know our Galaxy S6 Active owners are excited about the new Marshmallow update. I am excited about it too, as I wait for it to be released for my device. I understand the wait may be frustrating but we are working diligently to get the update to you.
We are putting the 6.0 update and your device through extensive testing to ensure full compatibility. Once we are sure that the Marshmallow update will successfully operate on your phone with no issues, we will release it to you. As of now, I don’t have a firm date for when this will happen. Rest assured, when available, you will receive an over the air notification on your device with step-by-step instructions to update your software.
For more updates and discussion about Marshmallow availability, please visit
https://forums.att.com/t5/Android/Marshmallow-Updates-amp-Discussion/m-p/4817255#M69781
Thank you so much for your patience!
Tim, Community Specialist
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I have been running a beta build since early May and have not run into any issues what so ever. All of the featured improvements work, battery life and device performance is significantly improved over 5.1.1. I cannot for the life of me understand why they are taking so long to approve the OTA.