All the functionality from Alpaca Trading API for direct users is supported under Broker API. Please read the documentation for more details. There are additional capabilities for Trading API in the broker setup.

Fractional Shares

Under the correspondent authentication, Trading API is extended for fractional shares trading.

Asset API

Asset entity has an extra field named fractionable with type boolean, it is set to true if the asset is marked for fractional trading. Check out more about our Assets API here.

Order API

The POST method (to submit order) has an extra parameter called notional to denote the dollar amount to buy. This parameter is mutually exclusive to the qty parameter. You can also specify the qty parameter with fractional quantity. Note that the fractional shares trading is currently supported only for market day orders and any other type of orders will result in API error. You can submit such fractional share orders in the night to execute at the next market open.

The order entity includes the notional value if the order was submitted with the notional value. In this case, the order entity omits the qty field.

Check out more about our Order API here.

Sample Order Object

    "id": "39c489ad-fcb1-42b3-9f62-e14c11c62157",
    "client_order_id": "a49c3e74-3f74-468e-a31a-f7a15de17128",
    "created_at": "2024-05-20T09:56:41.449735Z",
    "updated_at": "2024-05-20T13:30:00.876162Z",
    "submitted_at": "2024-05-20T13:23:01.24795Z",
    "filled_at": "2024-05-20T13:30:00.865454Z",
    "expired_at": null,
    "canceled_at": null,
    "failed_at": null,
    "replaced_at": null,
    "replaced_by": null,
    "replaces": null,
    "asset_id": "7595a8d2-68a6-46d7-910c-6b1958491f5c",
    "symbol": "A",
    "asset_class": "us_equity",
    "notional": null,
    "qty": "0.1",
    "filled_qty": "0.1",
    "filled_avg_price": "154.03",
    "order_class": "",
    "order_type": "market",
    "type": "market",
    "side": "sell",
    "time_in_force": "day",
    "limit_price": null,
    "stop_price": null,
    "status": "filled",
    "extended_hours": false,
    "legs": null,
    "trail_percent": null,
    "trail_price": null,
    "hwm": null,
    "commission": "0",
    "subtag": null,
    "source": "correspondent"

Order Properties

idstring/UUIDOrder ID generated by Alpaca
client_order_idstring/UUIDClient unique order ID
created_atstring/timestampTime when order was entered
updated_atstring/timestampTime of most recent change to the order
submitted_atstring/timestampTime the order was submitted for execution or, if not yet submitted the created_at time. Because orders are submitted for execution asynchronous to database updates, at times this may be before the created_at time.
filled_atstring/timestampTime the order was filled. Can be null if not filled
expired_atstring/timestampCan be null
cancelled_atstring/timestampCan be null
failed_atstring/timestampCan be null
replaced_atstring/timestampCan be null
replaced_bystring/UUIDThe order ID that this order was replaced by. (Can be null)
replacesstring/UUIDThe order ID that this order replaces. (Can be null)
asset_idstring/UUIDThe asset ID
symbolstringThe asset symbol
asset_classstringThe asset class
notionalstring/numberOrdered notional amount. If entered, qty will be null. Can take up to 2 decimal points.
qtystring/numberOrdered quantity. If entered, notional will be null. Can take up to 9 decimal points.
filled_qtystring/numberFilled quantity.
filled_avg_pricestring/numberFilled average price. Can be 0 until order is processed in case order is passed outside of market hours.
order_classstringValid values: simplebracketoco or oto.
order_typestring/number(Will be deprecated in favor of type field below) Valid values: market, limit, stop, stop_limit, trailing_stop
typestringValid values: market,limitstopstop_limittrailing_stop.
sidestringValid values: buy and sell.
time_in_forcestringPlease see the relevant section in Time in Force for more info on what values are possible for what kind of orders.
limit_pricestring/numberLimit price.
stop_pricestring/numberStop price.
statusstringOrder status. See Order statuses here.
extended_hoursbooleanIf true, eligible for execution outside regular trading hours.
legsarrayWhen querying non-simple order_class orders in a nested style, an array of Order entities associated with this order. Otherwise, null.
trail_percentstring/numberThe percent value away from the high water mark for trailing stop orders.
trail_pricestring/numberThe dollar value away from the high water mark for trailing stop orders.
hwmstring/numberThe highest (lowest) market price seen since the trailing stop order was submitted.
commissionstring/numberThe commission you want to charge the end user.
commission_typestringSelect how to interpret the value provided in the commission field.
Available options: notional(default), qty, bps.
subtagstring/numberAn account identifier for Omnibus partners. (Can be null)
sourcestringSource of order.

Account Configuration API

Account configuration API adds another configuration key called fractional_trading and defaults to true. If you want to disable fractional trading for a specific account for any reason, you can set this to false.


You have the option to charge the commission for each order. You will need to contact Alpaca first to set up the commission structure, but once it’s set up, you can submit customer orders with a commission parameter indicating the dollar amount to charge. The respective field is attached in the order entity in the API response.

To charge commissions, first select desired method with commission_type. Then specify the desired dollar amount or percentage in commission field.

  • notional:
    Charge commission on a per order basis. When the commission_type field is omitted from the order request, this is used as the default.
  • qty:
    Charge commission on a per qty/contract basis, pro rated.
  • bps:
    The percent commission you want to charge the end user on the order (expressed in bps). Alpaca will convert the order to a notional amount for purposes of calculating commission.

Order Sub-tagging (Omnibus)

If you are an omnibus setup, we ask you to submit a “sub-tag” value in each order. This is for us to understand the order flow better from the trade surveillance requirements. In case you fail to attach proper sub-tags, we may need to reject all of the order flows coming from you as we may not be able to segregate particular malicious activities.