Samsung Galaxy Tab S 10.5 starts grtting Android M update on AT&T network. The update itself Weighing 1,063MB and the new update brings along Android version 6.0.1 as well as security patch for the month of September.
Additionally, the update also includes the NumberSync feature that allows you to use your tablet to make and receive voice and video calls using your existing mobile number.
it may take some time for the update to hit your device. If you still did not get update you can check it manually by visiting setting menu.