Stream Reference

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Fast API provides multiple data streams for various exchange data:

• L2 Order Book Data
• Trade Events
• Per Account Order Events

Book Ticker

Schema	Frequency	Description
{symbol}@bookTicker	Real-time	Real time updates to the best bid/ask price for an order book.

Code
 
{
  "u": 1751505576085,
  "E": 1751508438600117161,
  "s": "btcusd",
  "b": "45000.50",
  "B": "1.25000000",
  "a": "45001.00",
  "A": "0.75000000"
}

Field	Type	Description
u	number	Update ID
E	number	Event time (nanoseconds)
s	string	Symbol
b	string	Best bid price
B	string	Best bid quantity
a	string	Best ask price
A	string	Best ask quantity

---

L2 Partial Depth Streams

Schema	Frequency	Description
{symbol}@depth5	Periodic (1s)	Periodic snapshot of the top 5 levels once per second
{symbol}@depth10	Periodic (1s)	Top 10 levels
{symbol}@depth20	Periodic (1s)	Top 20 levels
{symbol}@depth5@100ms	Periodic (100ms)	Top 5 levels every 100 milliseconds
{symbol}@depth10@100ms	Periodic (100ms)	Top 10 levels
{symbol}@depth20@100ms	Periodic (100ms)	Top 20 levels

Code
 
{
  "lastUpdateId": 12345678,
  "bids": [
    ["45000.50", "1.25000000"],
    ["45000.25", "0.50000000"]
  ],
  "asks": [
    ["45001.00", "0.75000000"],
    ["45001.25", "2.00000000"]
  ]
}

Field	Type	Description
lastUpdateId	number	Last update ID
bids	array	Array of [price, quantity]
asks	array	Array of [price, quantity]

---

L2 Differential Depth Streams

Schema	Frequency	Description
{symbol}@depth	Periodic (1s)	List of all changed price levels in the last second
{symbol}@depth@100ms	Periodic (100ms)	In the last 100 milliseconds

Code
 
{
  "e": "depthUpdate",
  "E": 1751508260659505382,
  "s": "btcusd",
  "U": 12345677,
  "u": 12345678,
  "b": [
    ["45000.50", "1.25000000"],
    ["45000.25", "0.00000000"]
  ],
  "a": [
    ["45001.00", "0.75000000"]
  ]
}

Field	Type	Description
e	string	Event type ("depthUpdate")
E	number	Event time (nanoseconds)
s	string	Symbol
U	number	First update ID in this event
u	number	Last update ID in this event
b	array	Bid updates [price, quantity]
a	array	Ask updates [price, quantity]

---

Trade Stream

Schema	Frequency	Description
{symbol}@trade	Real-time	Real time trade executions

Code
 
{
  "E": 1759873803503023900,
  "s": "btcusd",
  "t": 2840140956529623,
  "p": "120649.97000",
  "q": "0.0046190900",
  "m": true
}

Field	Type	Description
E	number	Event time (nanoseconds)
s	string	Symbol
t	number	Trade ID
p	string	Price
q	string	Quantity
m	boolean	Is buyer the maker

---

Order Events

Schema	Frequency	Description
orders@account	Real-time	Real time order activity for the account associated with the authenticated API key
orders@session	Real-time	Real time order activity for the authenticated API key

Code
 
# Order Event - New
{
  "E":1759291847686856569,
  "s":"BTCUSD",
  "i":73797746498585286,
  "c":"my-order-1759291847503",
  "S":"BUY",
  "o":"LIMIT",
  "X":"NEW",
  "p":"1.00000",
  "q":"0.0000100000",
  "z":"0.0000100000",
  "T":1759291847686856569
}

# Order Event - Canceled
{
  "E":1759291847731455006,
  "s":"BTCUSD",
  "i":73797746498585286,
  "c":"my-order-1759291847503",
  "X":"CANCELED",
  "T":1759291847731455006
}

Field	Type	Description
E	number	Event time (nanoseconds)
s	string	Symbol
i	number	Order ID
c	string	Client Order ID
S	string	Side, BUY / SELL
o	string	Type, LIMIT / MARKET
X	string	Status, NEW / OPEN / FILLED / PARTIALLY_FILLED / CANCELED / REJECTED / MODIFIED
p	string	Order price
P	string	Stop price
q	string	Original quantity
z	string	Remaining quantity
Z	string	Executed quantity. For FILLED / PARTIALLY_FILLED events, this is the quantity filled in the last execution. For CANCELED and other events, this is the cumulative quantity filled over the lifetime of the order.
L	string	Last execution price
t	number	Trade ID
r	string	Rejection reason
T	number	Update time (nanoseconds)
O	string	Event outcome for event contracts, YES / NO

Rejection Reasons

When an order is REJECTED, the r field contains one of:

Reason	Description
MarketNotOpen	Market is closed or paused
InsufficientFunds	Account lacks sufficient balance
InvalidPrice	Price violates constraints
LimitPriceOffTick	Price does not align with tick size
InvalidQuantity	Quantity below minimum or off increment
InvalidStopPrice	Stop price violates constraints
InvalidTotalSpend	Total spend calculation error
DuplicateOrder	Duplicate client order ID
InsufficientLiquidity	Not enough liquidity at price
UnknownInstrument	Trading pair does not exist

Cancellation Reasons

When an order is CANCELED by the system, the r field contains one of:

Reason	Description
SelfCrossPrevented	Self-trade prevention triggered
FillOrKillWouldNotFill	FOK order could not fill completely
ImmediateOrCancelWouldPost	IOC order would post to book
MakerOrCancelWouldTake	MOC order would take liquidity
AuctionCancelled	Auction-related cancellation
ExceedsPriceLimits	Price moved beyond limits

---

Balance Updates

Schema	Frequency	Description
balances@account	Real-time	Real time balance updates for the account associated with the authenticated API key
balances@account@1s	Periodic (1s)	Periodic snapshot of all balances every second for the account associated with the authenticated API key

The balances@account stream pushes updates in real time whenever a balance change occurs, and only includes the assets that changed. The balances@account@1s stream sends a complete snapshot of all account balances every second, regardless of whether they changed. On subscribe, balances@account@1s will immediately send the current balances if available.

Code
 
# Balance Update
{
  "e": "balanceUpdate",
  "E": 1768250434780,
  "u": 1768250421600,
  "B": [
    {
      "a": "USD",
      "f": "207.39"
    }
  ]
}

Field	Type	Description
e	string	Event type ("balanceUpdate")
E	number	Event time (nanoseconds)
u	number	Time of the last account update (nanoseconds)
B	array	Balance updates
a	string	Asset code
f	string	Asset balance