Kalshi Real-Time WebSocket

Connect to the Kalshi WebSocket for real-time price, orderbook, and trade updates.

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Connection

Connect to the WebSocket endpoint:

Code sample:

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

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Subscribing to Markets

Once connected, send a JSON message to subscribe to Kalshi markets using their klsi_id:

Code sample:

• {
• "action": "subscribe",
• "klsi_ids": ["KXBTCD-25FEB14-B55000", "KXETHD-25FEB14-B3100"],
• "message_types": ["prices", "orderbook", "trades"]
• }

Subscription Fields

Field	Type	Required	Description
action	string	Yes	subscribe or unsubscribe
klsi_ids	array	Yes	Array of Kalshi market identifiers
message_types	array	No	["prices"], ["orderbook"], ["trades"], or any combination. Defaults to prices and orderbook if omitted

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Unsubscribing

Code sample:

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

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Message Types

Price Messages

Real-time price updates for subscribed markets:

Code sample:

• {
• "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"
• }

Orderbook Messages

Real-time orderbook snapshots for subscribed markets:

Code sample:

• {
• "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"
• }

Trade Messages

Real-time trade executions for subscribed markets:

Code sample:

• {
• "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 JavaScript Example

Code sample:

• const ws = new WebSocket('wss://api.delphiterminal.co/ws/kalshi');
• ws.onopen = () => {
• console.log('Connected to Kalshi WebSocket');
• // Subscribe to markets
• 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 from WebSocket');
• };
• ws.onerror = (error) => {
• console.error('WebSocket error:', error);
• };

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Connection Details

Property	Value
Protocol	WebSocket (wss://)
Keepalive	Ping every 54 seconds
Timeout	60 seconds without pong
Max Message Size	512 KB

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Notes

• No authentication required for WebSocket connection
• You must 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
• Subscribe to specific message types to reduce message volume
• Trades must be explicitly requested (not included in default subscription)

GET /ws/kalshi

Response

101

WebSocket connection upgraded successfully