HTC 10 and One M9 getting the October security update at T-Mobile
If you own the HTC 10 or the One M9, then you are eligible for the October security update at T-Mobile USA. Your phone will remain on Android 6.0.1 and Android 6.0, respectively, so don't think that you'll get anything else but the usual bug fixes.
In case you haven't been notified on the update yet, you can try force push it onto your phone by heading to Apps / Settings, About, Software update, Check now. If doesn't show up on your smartphone, then you should try later since the update might be rolled out in stages.
Since this isn't a major OS update, it should require too much internal memory, but make sure you have at least 200MB free storage just in case.
While Samsung and HTC continue to deliver timely security updates, other handset makers are struggling to keep up with Google's patch releases. Not to mention that even Samsung and HTC don't offer the update each month for all their relatively new high-end smartphones.