Many Samsung devices compatible with Marshmallow have still not been updated to Marshmallow. The problem is compounded when it comes to carrier locked devices since the updates then have to go through a lengthy certification and testing process before they’re released by carriers. T-Mobile customers can rest a bit easy knowing that their carrier has now started testing Marshmallow for Galaxy S6 and Galaxy S6 Edge.
T-Mobile has a separate section on its support pages which list the devices that are in the process of being updated. We can see that the Marshmallow update for Galaxy S6 and Galaxy S6 Edge on Magenta has already passed the Manufacturer Development stage.
Testing is the next stage. T-Mobile will put the update through its paces to ensure that the firmware won’t cause any problems to devices on its network. Once the certification process is done the update is marked “Completed” and from then it’s only a matter of days before it’s released to end users.
It’s unclear right now how long T-Mobile is going to take but if history is any indication it may not take more than a couple of weeks from now to get this update out to Galaxy S6 and Galaxy S6 Edge owners on its network.