account_id overview

Every Plaid API request returns an accounts key with information about the account(s) affiliated with a user’s credentials:

{
  "accounts": [{
    "account_id": "vzeNDwK7KQIm4yEog683uElbp9GRLEFXGK98D",
    "balances": {
      "available": 100,
      "current": 110,
      "limit": null
    },
    "mask": "0000",
    "name": "Plaid Checking",
    "official_name": "Plaid Gold Checking",
    "subtype": "checking",
    "type": "depository"
  }],
  "numbers": [{
    "account": "9900009606",
    "account_id": "vzeNDwK7KQIm4yEog683uElbp9GRLEFXGK98D",
    "routing": "011401533",
    "wire_routing": "021000021"
   }],
  "item": {Object},
  "request_id": "45QSn"
}

Each account’s _id property is unique. 

An account's _id will not change, except when Plaid is unable to match the account as it is stored in our system with the data returned by the financial institution. This may occur, for example, when the name of the account changes substantially. In cases like this, a new account _id will be assigned to the account. Additionally, if an access_token is deleted, and the same credentials that were used to generate that access_token are used to generate a new access_token on a later date, the new account _id will be different from the account _id affiliated with the original access_token.

Plaid’s system automatically detects when accounts are opened or closed. If an account is closed, the account and any transactions associated with that account will no longer be returned in API responses.