Instagram Stories let you send disappearing messages to your friends, but until now, you had to send them to all your friends. That's changing now, though, as Instagram has announced a new feature that lets you pare your audience for certain Stories down to just a select subset of your followers.
The feature is called Close Friends. You can add and remove followers from the list at any time; they won't know. The list can be accessed from the side menu on your profile. After setting it up, when you share a Story, you'll have the option to send it to all your followers, or just your smaller Close Friends list.
The feature is for sharing "more personal moments," according to Instagram — or moments you don't necessarily want your tech-savvy grandmother to see. While followers won't be notified if they're added to or removed from your Close Friends list, a badge appears in the Stories of people whose Close Friends lists you're on, so it's not totally secret. Assuming everything on social media is public is still probably safest.