iOS 11 Download Size
The iOS 11 GM could provide us with some clues but it probably won't reveal the exact size of the final version of iOS 11 for your device.
If you're getting close to your device's storage limit, you'll want to watch for details regarding the iOS 11 download size.
The iOS 11 update probably won't require 10GB of space but download sizes will differ based on device and your version of iOS 10.
If you're upgrading from iOS 10.3.3 your iOS 11 download will be the smallest. If you're coming from an update like iOS 10.2.1, your iOS 11 update will be much larger due to the features and fixes you missed in more recent iOS 10 updates.
If you only have a few MB of storage available on your phone or tablet, now would be a good time to do some cleanup.
If you don't want to delete a ton of files, it might be a good idea to wait for the iOS 11 release (GM or final) so that you can get a better idea about what you're up against.