Apple released an iOS update in the middle of the night. It appears to have pushed the 11.2 schedule forward thanks to a date looping bug.
The timeline for release of iOS 11.2 has clearly been moved forward to accommodate users affected by the December 2nd date bug, which was causing iPhones to Springboard crash consistently if certain apps using local notifications were installed.
If you are affected by the repeated crashing bug, which started happening for users worldwide after 12:15 AM on December 2nd, you will need to disable notifications as soon as possible as a workaround. You can then jump to Software Update to install the update.
The release notes mention the inclusion of Apple Pay Cash, which enables peer-to-peer payments between friends in the US, but it is not yet live.
The update also enables support for faster 7.5W Qi wireless charging. If you have an iPhone 8 or an iPhone X as well as a wireless charger that supports 7.5W or more, your phone will now charge more quickly as Apple first limited wireless charging to 5W.
iOS 11.2 also addresses other high-profile bugs, including a fix that prevented fast number entry into the Calculator app, strange autocorrect suggestions, and other tweaks.