Today, Apple issued the fourth Developer beta of iOS 12.1.3 to all devices capable of running iOS 12. This update comes in two days after Apple released the third Developer beta of iOS 12.1.3 on Monday, so it was likely Apple found a glaring security issue or bug which needed to be addressed right away.
Apple has been working on iOS 12.1 for a while now, with its original introduction on October 30th with Group FaceTime and eSIM for iPhone XS, iPhone XS Max and iPhone XR. In November, Apple released iOS 12.1.1 with FaceTime UI improvements and Live Photo captures, and most recently  iOS 12.1.2 included cellular connectivity fixes and eSIM activation bug fixes for the latest iPhone models.
It is unclear when Apple will begin Developer testing of iOS 12.2, which should be launching as a final release in March, according to The Verifier, who predicted iOS 12.1’s release very accurately.
Coming back to iOS 12.1.3 beta 4, we’ve seen some indications in 12.1.3 that Apple has added some code to be able to change the animation behavior remotely, when force closing apps in China ”“ which is a new change to satisfy courts in China about a Qualcomm patent ban.