T-Mobile 's HTC One A9 receives a security update
The promise does not apply to carrier-branded versions of the One A9, like the T-Mobile variant of the handset. As it turns out, the latter received its security update today, taking the phone's security patch level to August 1st. The update weighs in at 596.71MB, and is software version 3.39.531.12.
Because the update is sent out OTA, it is disseminated on a staggered basis. That means that you might not receive it for a few days. No need to panic. Eventually the update will hit your phone. And if you want to try to pull it out manually, you can go to Settings > About > Software update > Check Now.
Once you receive notification that the update has hit your T-Mobile HTC One A9, make sure that you are connected to a Wi-Fi network and that your battery is fully charged before you start the rest of the process.