Apple released a version of iOS for the iPhone 4S, and I'm sure there are plenty of people who are nervous about installing it. This device is four years old, and four new models have come out since its release, so it's possible the iPhone 4S just isn't up to a new operating system. Fortunately, that's not the case. I loaded iOS 9 onto a 4S on the day this new version was introduced and have been using it ever since, and have had no problems. In fact, it's possible the device runs better with this upgrade than it did with iOS 8, which was poorly written from Day 1. Don't get me wrong, this is still an elderly phone and a new OS isn't going to turn it into a speed demon, but it's certainly no slower or more unstable than it was before... except possible the Camera app, which can take a few seconds to open. I also installed iOS 9.0.1 when it came out a few days ago and have continued to have no significant problems.