The new feature is currently in testing.
The feature will be made possible by the timestamps creators provide in the description box of their videos. This means that if they do not list any, YouTube won’t be able to make its own.
While Chapters will utilize timestamps, they are different in that they appear along the progress bar of the video in sections, and that hovering over one will show viewers to name of said chapter, which will be provided by the creator.
YouTube shares that it’s testing the feature on a small section of videos across desktop, iOS and Android devices while it waits to gather feedback. Those who wish to opt-out of the testing need only adjust the timestamp in their video’s description box from 0:00 to 0:01.
As the Chapters feature is currently in testing, it’s unknown when or if it will see a global rollout.