Xcode 12.3 Beta 1 was released on 12 Nov 2020 and requires macOS 10.15.4+.
It can be downloaded from https://download.developer.apple.com/Developer_Tools/Xcode_12.3_beta/Xcode_12.3_beta.xip.
Release notes are located at https://developer.apple.com/documentation/xcode-release-notes/xcode-12_3-beta-release-notes.
The SDKs it contains are:
- iOS 14.3 (Build 18C5044f)
- macOS 11.1 (Build 20C5048g)
- tvOS 14.3 (Build 18K5545f)
- watchOS 7.2 (Build 18S5545f)
The compilers it contains are:
- clang 12.0.0 (Build 1200.0.32.28)
- swift 5.3.2 (Build 1200.0.44.1)