After releasing iOS 12.0.1 to the public yesterday, Apple has followed up by releasing the third beta of iOS 12.1 to developers signed up in the company's developer program. The final version of iOS 12.1 when released is expected to add eSIM support to the new lineup of iPhones on Verizon, AT&T and T-Mobile.
Additionally, the update will also give iPhone users the ability to adjust the depth control while taking a photo, in real time. Currently, you can only make adjustments to your photos after they have been shot. With depth control photographers w to adjust just how blurry the background appears on a portrait. The new update to iOS will also bring emoji and Group FaceTime support for up to 32 people.
If you are a registered developer, you can downloaded the iOS 12.1 Beta 3 update as an IPSW link from developer.apple.com or directly as an OTA update from Settings > General > Software Update on your device.
source - Apple