Apple released iOS 8.0.2 on September 25. iOS 8 is recommended for iPhone 5 and up according to Apple Genius's. Although, the iPhone 4s can receive the update to go to iOS 8. Just know that there will be some lagging in your iPhone while it preforms simpler tasks. Here are some ways to fix this lagging. I would recommend that you turn off spotlight search if you never use it. To do this go to settings, general, then spotlight search and uncheck everything. The next thing you can do is reduce the motion on you iPhone, which will remove moving apps and your background when you turn the devise. To do this go to settings, then general, then accessibility, then reduce motion and slide it on. The last thing you can do is reduce transparency. To do this go to settings, then general, then accessibility, then increase contrast, then turn on reduce transparency. On the iPhone 5 and up you won't have to do these changes to make iOS 8 run smoothly on you iPhone. Apple is expected to release iOS 8.1 on October 20th, it is rumored that this update will provide performance enhancements to the iPhone 4s.