Message reference

Four channel types, one envelope. Every message arrives wrapped in:

{"channel": "dist:fomc-2026-04-29", "data": { ... }}

The wrapper has exactly two top-level fields: channel (string) and data (object). Filter your message handler on channel, not on a type field — there is no type field in the wire format.

Channel types

Channel	Subscribe to	Description	Tier
dist	`dist:fomc-2026-04-29`	Cross-venue probability distribution for all outcomes	Free
book	`book:fomc-2026-04-29:hold`	Normalized orderbook updates for one outcome	Pro
trade	`trade:fomc-2026-04-29:hold`	Trade executions for one outcome	Pro
snapshot	`snapshot:fomc-2026-04-29`	Full state reset every 60s for all outcomes	Pro

dist and snapshot are event-level channels — subscribe with just the event_key. book and trade are per-outcome channels — append :{outcome_key} (use ?expand=channels on /feeds/catalog to get a ready-to-paste list). snapshot payload differs from dist: snapshot wraps the per-outcome list under data.distribution and adds full orderbook state per outcome. dist uses data.outcomes.

Distribution

Shows the market-implied probability for every outcome in an event, combining data from both venues.

{
  "event_key": "fomc-2026-04-29",
  "seq": 312,
  "published_ts": 1773892530947,
  "outcomes": [
    {
      "outcome": "hold",
      "label": "Fed maintains rate",
      "kalshi_prob": 0.945,
      "poly_prob": 0.955,
      "prob": 0.9479,
      "kalshi_depth_usd": 4714197.04,
      "poly_depth_usd": 1965879.48
    }
  ],
  "total_kalshi_depth_usd": 4784397.57,
  "total_poly_depth_usd": 2104564.65,
  "reference": {
    "source": "binance",
    "symbol": "BTCUSDT",
    "spot_bid": 68641.30,
    "spot_ask": 68641.31,
    "spot_mid": 68641.30,
    "futures_mark": 68723.51,
    "funding_rate": -0.00002124,
    "volume_24h": 951752117.03,
    "ts": 1774246512319
  }
}

Field	Description
`prob`	Combined probability, weighted by each venue’s liquidity. Kalshi at 94.5% with 4.7M USD depth + Polymarket at 95.5% with 2.0M USD depth = 94.79%.
`kalshi_prob` / `poly_prob`	Each venue’s YES mid-price (best bid + best ask) / 2. Null if that venue has no data.
`kalshi_depth_usd` / `poly_depth_usd`	Total USD within +/-5c of mid on each venue. Shows how much liquidity backs each probability.
`reference`	External reference data (e.g., Binance spot/futures for crypto events). Only present on enriched feeds. See crypto feed for field details.

Book update

Normalized orderbook updates from both venues. Prices are contract prices (0-1), sizes are absolute quantities. Derived fields like best bid/ask, mid, spread, and depth are pre-computed on every update.

{
  "event_key": "fomc-2026-04-29",
  "outcome": "hold",
  "venue": "polymarket",
  "token": "yes",
  "venue_id": {
    "condition_id": "0x36e8ca2...",
    "token_id": "63586620628..."
  },
  "seq": 4217,
  "exchange_ts": 1773892530351,
  "received_ts": 1773892530360,
  "published_ts": 1773892530363,
  "update_type": "delta",
  "levels": [
    {"side": "bid", "price": "0.955", "size": 8300.00},
    {"side": "ask", "price": "0.965", "size": 0}
  ],
  "best_bid": "0.955",
  "best_ask": "0.965",
  "mid": "0.960",
  "spread": "0.010",
  "bid_depth_usd": 47141.97,
  "ask_depth_usd": 23456.78,
  "reference": { ... }
}

Field	Description
`venue_id`	Identifiers to execute on the venue. Kalshi: market ticker. Polymarket: condition ID + token ID.
`update_type`	”snapshot” = full book replacement. “delta” = only changed levels. Size of 0 = level removed.
`levels`	Price levels with side (bid/ask), price (0-1), and size (absolute quantity after this update).
`best_bid` / `best_ask` / `mid` / `spread`	Pre-computed from full cross-token book state, not just the levels in this update.
`bid_depth_usd` / `ask_depth_usd`	Total USD within +/-5c of mid on bid and ask sides.
`reference`	External reference data for enriched feeds. Only present on crypto events. Omitted for macro.

Trade

Every trade execution from both venues, including the specific contract traded, price, quantity, and a venue-provided trade ID.

{
  "event_key": "fomc-2026-04-29",
  "outcome": "hold",
  "venue": "kalshi",
  "token": "no",
  "action": "buy",
  "venue_id": {"market_ticker": "KXFEDDECISION-26APR-H0"},
  "seq": 89,
  "exchange_ts": 1773892530000,
  "received_ts": 1773892530008,
  "published_ts": 1773892530010,
  "price": "0.06",
  "qty": 136.00,
  "trade_id": "a4d77927-dafe-5bde-53ed-80f6129cfd19",
  "reference": { ... }
}

Timestamps

Every book and trade message carries four timestamps (Unix ms) for end-to-end latency decomposition.

Field	Description
`exchange_ts`	When the exchange says the event occurred. Null if not provided by the venue.
`received_ts`	When we read the raw message off the venue WebSocket.
`published_ts`	When the normalized message was published internally.
`gateway_ts`	When the gateway sent the message to your WebSocket.

Getting started

WebSocket feeds

Whale tracking

Arbitrage

Search

Historical bars

Kalshi

Polymarket

Channel types

Distribution

Book update

Trade

Timestamps

​Channel types

​Distribution

​Book update

​Trade

​Timestamps

Channel types

Distribution

Book update

Trade

Timestamps