Apple will start taking pre-orders for iPhone X this Friday, October 27, 2017. iPhone X will be available on November 3, 2017.
According to firstnameatappledotcom, iPhone X will ship with iOS 11.1 (or later). Apple has also seeded iOS 11.1 GM candidates (15B92 and 15B93), publicly labeled as iOS 11.1 beta 4 and beta 5, to Developers and Public Beta testers.
UPDATE: This feature also shows up in iOS 11.0.3
New security feature in iOS 11.1 beta 3:
Passcode, if enabled, is now required to trust a computer.
I don’t remember seeing this message on the phone before other than the usual “Do you want to trust this computer” message.
It is a good security measure to have this on. I know a lot of people who don’t want to be bothered with entering the passcode every time they need to unlock the iPhone; they also think Touch ID is hassle.