# Memory ids

> One memory per conversation. A memory only grows, so a branch or an edit is a new memory.

A memory is one conversation. Its id is the only scope there is: every read and write names it, a request without one is refused, and recall searches within that one memory, never across your other memories.

## The shape

`POST /memories` returns the id. It is `mem_` followed by 24 letters and digits, for example `mem_8fK2qLmN4pR7sT1vW3xY5zA9`. Store it next to your own conversation id; you can also put your id in the memory's `metadata` (up to 16 string pairs).

```ts
const { id } = await memory.memories.create({ metadata: { conversation: 'c_123', user: 'u_9' } });
```

A memory belongs to the project of the key that created it. A key can only reach its own project's memories; any other id answers `404 not_found`.

## One per conversation

Create a memory when a conversation starts and use it for every call in that conversation, tool loops included. Two conversations never share a memory: facts from one would be recalled into the other.

A conversation can run for months. There is no length at which you need a new memory; that is what forgetting is for.

## A memory only grows

Messages are appended, never rewritten. That has two consequences:

- **Editing a past message** (the user edits turn 12 and regenerates): start a new memory. Send it the conversation as it now stands, up to the edit, in its first `decorate`.
- **Branching** (two continuations from one point): each branch is its own memory, seeded the same way.

Only what is new since the last call belongs in `newMessages`. The one exception is the model's last reply, which is recognised and not stored twice; any other message you send again is stored again, as new.

## Deleting and exporting

- `memory.memories.delete(id)` removes everything the memory holds and checks it is gone before it returns. It cannot be undone.
- `memory.memories.export(id)` returns every message, episode and fact as JSON.

See [Security](https://threadlessai.com/security) for what is stored and how deletion is verified.