NIP-40

Expiration timestamps

NIP-40 gives events an expiration timestamp. That lets a post or record say “this should stop being shown after this time,” which is useful for temporary announcements, offers, or short-lived status updates.

It does not guarantee every copy disappears, but it gives cooperative relays and clients a clear instruction. Think of it like a flyer with an event date: after the date passes, most places stop displaying it.

Read more in the official 40.md NIP document.