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Connection

Connect to the Kalshi WebSocket endpoint: 
wss://api.delphiterminal.co/ws/kalshi
No authentication is required for WebSocket connections.
PropertyValue
ProtocolWebSocket (wss://)
KeepalivePing every 54 seconds
Timeout60 seconds without pong
Max Message Size512 KB

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Subscribing to markets

Once connected, send a JSON message to subscribe using klsi_id: 
{
  "action": "subscribe",
  "klsi_ids": ["KXBTCD-25FEB14-B55000", "KXETHD-25FEB14-B3100"],
  "message_types": ["prices", "orderbook", "trades"]
}
FieldTypeRequiredDescription
actionstringYessubscribe or unsubscribe
klsi_idsarrayYesArray of Kalshi market identifiers
message_typesarrayNo["prices"], ["orderbook"], ["trades"], or any combination. Defaults to prices and orderbook if omitted

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Unsubscribing

{
  "action": "unsubscribe",
  "klsi_ids": ["KXBTCD-25FEB14-B55000"]
}

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Message types

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Price messages

Real-time price updates for subscribed markets: 
{
  "klsi_id": "KXBTCD-25FEB14-B55000",
  "price": 0.65,
  "yes_bid": 0.64,
  "yes_ask": 0.66,
  "volume": 15000,
  "open_interest": 8500,
  "last_update": "2026-02-03T14:30:00Z"
}

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Orderbook messages

Real-time orderbook snapshots for subscribed markets: 
{
  "klsi_id": "KXBTCD-25FEB14-B55000",
  "bid_side": [0, 0, 0, "...", 150, 200, 100],
  "ask_side": [100, 150, 200, "...", 0, 0, 0],
  "last_update": "2026-02-03T14:30:00Z"
}

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Trade messages

Real-time trade executions for subscribed markets: 
{
  "id": "trade123",
  "klsi_id": "KXBTCD-25FEB14-B55000",
  "exchange": "klsi",
  "yes_price": 0.65,
  "no_price": 0.35,
  "count": 10,
  "taker_side": "buy",
  "last_update": "2026-02-03T14:30:00Z"
}

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Full example

const ws = new WebSocket("wss://api.delphiterminal.co/ws/kalshi");

ws.onopen = () => {
  console.log("Connected to Kalshi WebSocket");

  ws.send(JSON.stringify({
    action: "subscribe",
    klsi_ids: ["KXBTCD-25FEB14-B55000"],
    message_types: ["prices", "orderbook", "trades"]
  }));
};

ws.onmessage = (event) => {
  const data = JSON.parse(event.data);
  console.log("Received:", data);
};

ws.onclose = () => console.log("Disconnected");
ws.onerror = (error) => console.error("WebSocket error:", error);

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Important notes

  • No authentication required for WebSocket connections
  • Use klsi_id (Kalshi market identifier) to subscribe
  • Messages are only sent for markets you have explicitly subscribed to
  • Multiple markets can be subscribed in a single message
  • Trades must be explicitly requested (not included in the default subscription)