Apple has released the first iOS 12.1.1 beta with build the number 16C5036c. Apple also released the first tvOS 12.1.1 beta with build number 16K5035b, and the first macOS Mojave 10.14.2 beta which build is number 18C31g.
At this stage, nothing is known about the contents of each beta. Users need to have the developer beta profile installed for this beta.
Update: The Live Photos feature returns, but both devices must be updated to use it.
Update 2: Apple has pulled the MacOS Mojave 10.14.2 beta, no details have been given as to why but Apple also pulled WatchOS 5.1 yesterday after users were reporting it bricking their device.