GDC every year is like the tech convention for the game industry where they talk about new techniques used and things they learned. This year multitasking in The Sims 4 will be discussed by two software engineers.
Date and time of this talk is unknown right now, also is unknown if it will be live streamed or recorded so we can see it afterwards. We will let you know as soon as we find out!
Here is the link to the schedule: http://schedule.gdconf.com/session-id/826160
This system allows Sims in The Sims 4 to convincingly eat, watch TV, chat with other Sims, express emotion, and perform many more behaviors simultaneously.
Thanks to @SimsVIP for finding this!