Update: On January 17, Apple revealed that iOS 17.3 will be released "next week", with Monday, January 22, and Tuesday, January 23, being the most likely dates.
Apple is working on an iOS 17.3 update, and has seeded three betas to developers and public beta testers so far. The update isn't quite as large as the prior iOS 17.2 update in terms of new features so the testing period won't be as long, and we are expecting it to launch before the end of January.
In terms of timing, a launch the week of January 22nd might make the most sense. We've had three betas, two of which have not added anything particularly notable, suggesting there isn't much testing left. If Apple plans to launch the update on the 22nd or the 23rd, we can expect to see the release candidate version of the iOS 17.3 update on the 15th, followed by the launch.
Apple could also release iOS 17.3 on the week of the 29th, but that is the week that visionOS and the Vision Pro headset will be coming out. Apple does sometimes tie software release updates together, but as an entirely new operating system, visionOS isn't likely to be accompanied by any other updates.
The last new operating system update that Apple came out with was watchOS back in 2015. watchOS saw its official release on Friday, April 24, 2015, the same day that the first Apple Watch models launched.
Apple last year released iOS 16.3 on January 23, and in 2022, Apple released iOS 15.3 on January 26, so a January 22 launch date for iOS 17.3 would be in line with Apple's past release timelines.
iOS 17.3's main new feature is Stolen Device Protection, a feature that prevents a thief that somehow gains access to both your iPhone and your passcode from accessing sensitive information. It locks several features behind a Face ID scan, preventing a thief from viewing iCloud Keychain passwords, turning off Lost Mode, using Safari payment methods, and more.
It also adds a time-based delay before allowing Face ID, Find My, or Stolen Device Protection to be turned off, and before letting an Apple ID or iPhone passcode be changed.
Along with Stolen Device Protection, iOS 17.3 adds Collaborative Apple Music Playlists, a feature originally intended for iOS 17.2. With Collaborative Playlists, multiple people can contribute to one shared Apple Music playlist.