According to XperiaBlog, firmware build 6.1.1.B.1.89 was certified by PTCRB a few months ago for all Xperia smartphones powered by NovaThor chipsets.
For the time being, the update has been spotted in Italy, as TIM-branded Xperia U devices have been reportedly receiving the new firmware version via Sony PC Companion.
Unfortunately, Sony did not confirm the global rollout of the update yet, though we can expect firmware version 6.1.1.B.1.89 will be made available to all Xperia U units pretty soon.
So far, users who installed the update report important system improvements and performance enhancements. Stay tuned for more info on the matter.