IGSID
An IGSID, or Instagram-Scoped ID, is the stable identifier Instagram assigns to a person for their conversations with a specific app or business through the messaging API. It stays the same across messages so tools can recognize returning people, but it differs from the person's public account ID and from their IGSID with other apps.
Why it matters for creators
The IGSID is how an automation tool tells people apart and remembers them. When someone who commented on last month's reel replies to today's story, the tool sees the same IGSID and can treat them as a returning person — already sent the guide, already asked the welcome question — instead of starting from zero.
It's also a privacy boundary. Because the ID is scoped to one app, tools can't use it to follow a person's activity across other apps, and it isn't their public account ID. For you it mostly stays invisible: it's the key your contact list is built on.