Apple has already updated iOS to iOS 9.0.1, pushing out a small update to address some potentially major bugs. You can download the update via Settings > General > Software Update, or through iTunes. For those who have successfully updated to iOS 9.0 already, it’s a 35 MB download for an iPhone 6, so it’s probably easiest to update over the air, rather than via iTunes.
That said, the main fix in iOS 9.0.1 is for an issue that made the Slide to Upgrade screen unresponsive, forcing users to restore their devices in order to perform the update. This will benefit those who waited to upgrade to iOS 9.0, as we suggested was a prudent course of action in “iOS 9: TidBITS Answers Your Questions” (16 September 2015).
iOS 9.0.1 also fixes bugs that prevented alarms and timers from playing, caused distorted frames when pausing video in Safari and Photos, and could cause users with custom APNs to lose cellular data.
We’ve heard from readers that iOS 9.0.1 resolves some two-step authentication problems that 9.0 users experienced when updating via iTunes, and images from at least one camera (the Sony A6000) that couldn’t be downloaded via the Apple iPad Camera Connection Kit when using 9.0 now can be transferred in 9.0.1.
Apple’s release notes imply that there are security improvements in iOS 9.0.1, but the company’s security updates site does not include a listing for the update.
After updating to iOS 9.0.1, your recently updated apps may need to be updated again. If Updates is enabled in Settings > App and iTunes Stores, this will happen automatically.