Apple has released the third beta of iOS 12.1.3 to developers.
Being the first beta this year, the contents of this update are expected to be small as it's a 'point' release that contains bug fixes. We will update you if any larger changes are spotted soon.
Previous betas contained some fixes to address issues in China with Qualcomm. With the previous iOS 12.1.2 update, a new animation was found when closing apps, but only for users in China. We may get it with this beta.
Updates when we get them, and if Beta 3 is released to the public program. watchOS 5.1.3 beta is now out as well, most likely containing fixes.