API reference

Event detail: every venue's prices

One event with every venue market, every outcome's quote, how outcomes match across venues, and the price gap for each matched outcome.

When to use it

Show Kalshi and Polymarket prices for the same answer side by side.
Get each outcome's id for price history and its stream ids for the WebSocket.
Read the cross-venue spreads for one event.

How to read it

markets[] has one entry per venue listing. markets[].outcomes[] are the answers on that venue.
Each outcome's quote has the price (probability), bid and ask, and freshness. Quotes come from the venue's live feed when TPM has it (source: "live"), otherwise from the latest poll.
Outcomes with the same match.group_id are the same answer on different venues.
spreads[] gives, per matched outcome (outcome_key equals match.key), the cheapest venue to buy Yes, the best venue to sell it, and the gap between them.
Before treating two prices as one bet, check comparison and match.contract_compatibility. Only verified means a person checked the rules match.

Gaps are gross

gap is sell bid minus buy ask, before fees and order-book depth. A positive gap is a lead to check, not guaranteed profit.

GET/api/public/v1/events/{slug}API key required

Get one event

The sample is trimmed to one outcome per venue; the real response lists every outcome.

Parameters

Name	In	Type	Required	Default	Description
slug	path	string	Yes	—	Event slug from `/events`.

Request

curl -s 'https://api.thepredictionmarkets.com/api/public/v1/events/democratic-presidential-nominee-2028' \
  -H 'X-API-Key: tpm_demo_key_authorized_2026'

Response

Example 200 response. Values are illustrative and change over time.

200 OK

{
  "data": {
    "id": "4d633d66-f3da-4f36-b04c-ce41b26bb13a",
    "slug": "democratic-presidential-nominee-2028",
    "title": "Democratic Presidential Nominee 2028",
    "question": "Democratic Presidential Nominee 2028",
    "category": "politics",
    "status": "active",
    "end_date": "2028-11-07T00:00:00Z",
    "resolution": {
      "outcome": null,
      "summary": "Resolves Yes if the named individual wins and accepts the 2028 Democratic nomination for U.S. president.",
      "resolved_at": null
    },
    "comparison": "comparable",
    "volume": 1540934033.49,
    "venues": [
      "kalshi",
      "polymarket"
    ],
    "markets": [
      {
        "venue": "kalshi",
        "market_id": "KXPRESNOMD-28",
        "title": "Democratic Presidential Nominee 2028",
        "url": "https://kalshi.com/markets/kxpresnomd",
        "status": "active",
        "event_slug": "democratic-presidential-nominee-2028",
        "volume": 244696381.96,
        "liquidity": null,
        "end_date": "2028-11-07T00:00:00Z",
        "last_seen_at": "2026-10-21T08:24:28Z",
        "outcome_count": 41,
        "outcomes": [
          {
            "id": "5c66f06e-dcac-44fa-93af-ba710d2a9ed2",
            "title": "Gavin Newsom",
            "contract_id": "KXPRESNOMD-28-GN",
            "status": "active",
            "volume": 11138438.36,
            "probability_change_24h": null,
            "quote": {
              "probability": 0.16,
              "best_bid": 0.16,
              "best_ask": 0.17,
              "spread": 0.01,
              "source": "live",
              "observed_at": "2026-10-21T08:38:56Z",
              "age_seconds": 3,
              "freshness": "live"
            },
            "stream": {
              "provider": "kalshi",
              "market_id": "KXPRESNOMD-28-GN",
              "outcome_id": "yes"
            },
            "match": {
              "group_id": "b5f0c3d2-6a1e-5f7b-9c2d-1e8a4f3b7d60",
              "key": "candidate:gnew",
              "state": "AUTO_MATCHED",
              "contract_compatibility": "unverified"
            }
          }
        ],
        "rules": null
      },
      {
        "venue": "polymarket",
        "market_id": "democratic-presidential-nominee-2028",
        "title": "Democratic Presidential Nominee 2028",
        "url": "https://polymarket.com/event/democratic-presidential-nominee-2028",
        "status": "active",
        "event_slug": "democratic-presidential-nominee-2028",
        "volume": 1296237651.53,
        "liquidity": 74355239.4,
        "end_date": "2028-11-07T00:00:00Z",
        "last_seen_at": "2026-10-21T08:37:22Z",
        "outcome_count": 128,
        "outcomes": [
          {
            "id": "e11fcb39-5832-455d-97df-7d25816b33f3",
            "title": "Gavin Newsom",
            "contract_id": "0x0f49db97f71c68b1e42a6d16e3de93d85dbf7d4148e3f018eb79e88554be9f75",
            "status": "active",
            "volume": 28018699.72,
            "probability_change_24h": null,
            "quote": {
              "probability": 0.1635,
              "best_bid": 0.163,
              "best_ask": 0.164,
              "spread": 0.001,
              "source": "snapshot",
              "observed_at": "2026-10-21T08:37:22Z",
              "age_seconds": 94,
              "freshness": "fresh"
            },
            "stream": {
              "provider": "polymarket",
              "market_id": "0x0f49db97f71c68b1e42a6d16e3de93d85dbf7d4148e3f018eb79e88554be9f75",
              "outcome_id": "54533043819946592547517511176940999955633860128497669742211153063842200957669"
            },
            "match": {
              "group_id": "b5f0c3d2-6a1e-5f7b-9c2d-1e8a4f3b7d60",
              "key": "candidate:gnew",
              "state": "AUTO_MATCHED",
              "contract_compatibility": "unverified"
            }
          }
        ],
        "rules": null
      }
    ],
    "spreads": [
      {
        "outcome_key": "candidate:acor",
        "gap": 0.024,
        "buy": {
          "venue": "kalshi",
          "price": 0.14
        },
        "sell": {
          "venue": "polymarket",
          "price": 0.164
        }
      },
      {
        "outcome_key": "candidate:gnew",
        "gap": -0.004,
        "buy": {
          "venue": "polymarket",
          "price": 0.164
        },
        "sell": {
          "venue": "kalshi",
          "price": 0.16
        }
      }
    ],
    "web_url": "https://thepredictionmarkets.com/odds/democratic-presidential-nominee-2028"
  }
}

Response fields

Field	Type	Description
id, slug, title	string	Event identity, as in `/events`.
question	string \| null	The question in full, when it differs from the title.
category, status, end_date	string \| null	As in `/events`.
resolution	object	`{outcome, summary, resolved_at}`. `summary` describes how it settles; `outcome` is set once resolved.
comparison	string \| null	`verified`: venues list the same bet. `comparable`: similar, check the rules. Absent for one venue.
volume	number \| null	Total volume across venues, US dollars.
venues	string[]	Venues listing it.
markets[]	Market[]	One per venue listing; fields as in markets.
markets[].outcomes[].id	string	TPM outcome id. Stable; use it for `/history?outcome_id=`.
markets[].outcomes[].title	string	The answer this outcome represents, e.g. `Gavin Newsom` or `Yes`.
markets[].outcomes[].contract_id	string \| null	The venue's tradable contract: a Kalshi market ticker or a Polymarket condition id. Use it with `/prices`.
markets[].outcomes[].status	string \| null	Venue status of the contract, e.g. `active`.
markets[].outcomes[].volume	number \| null	Traded volume in US dollars, as the venue reports it.
markets[].outcomes[].probability_change_24h	number \| null	Change in probability over 24 hours, when known.
markets[].outcomes[].quote.probability	number \| null	The displayed price as a probability from 0 to 1, using the venue's own display rule. 0.16 means a 16% implied chance.
markets[].outcomes[].quote.best_bid	number \| null	Highest price someone will pay for Yes right now.
markets[].outcomes[].quote.best_ask	number \| null	Lowest price someone will sell Yes for right now.
markets[].outcomes[].quote.spread	number \| null	`best_ask - best_bid` on this venue (not the cross-venue gap).
markets[].outcomes[].quote.source	"live" \| "snapshot"	`live`: from the venue's WebSocket feed. `snapshot`: from TPM's REST poll of the venue.
markets[].outcomes[].quote.observed_at	string \| null	When this price was last known to be current (UTC).
markets[].outcomes[].quote.age_seconds	integer \| null	Seconds since `observed_at`.
markets[].outcomes[].quote.freshness	string	`live`, `fresh`, `aging`, `stale` or `unknown`. See freshness.
markets[].outcomes[].stream	object \| null	`{provider, market_id, outcome_id}`: send these to subscribe on the WebSocket.
markets[].outcomes[].match.group_id	string \| null	Outcomes with the same `group_id` on different venues are the same answer.
markets[].outcomes[].match.key	string \| null	Readable outcome key, e.g. `candidate:gnew` or `binary:yes`. Joins with `spreads[].outcome_key`.
markets[].outcomes[].match.state	string \| null	How the link was made, e.g. `AUTO_MATCHED` or `MANUAL`.
markets[].outcomes[].match.contract_compatibility	string \| null	`verified` only when a person checked that both venues settle the same way; otherwise `unverified`.
spreads[].outcome_key	string	The matched outcome (`match.key`).
spreads[].gap	number \| null	Sell bid minus buy ask across venues. Gross: before fees and depth.
spreads[].buy	{venue, price} \| null	Cheapest venue to buy Yes (its ask).
spreads[].sell	{venue, price} \| null	Best venue to sell Yes (its bid).
web_url	string	The event page on thepredictionmarkets.com.

Errors

HTTP	Code	When
404	not_found.event	No event has this slug.
401	auth.missing_key	No `X-API-Key` header was sent.
401	auth.invalid_key	The key is wrong or was revoked.
429	rate_limit.per_second	Too many requests this second. Wait for `Retry-After`.

404 not_found.event

{
  "error": {
    "code": "not_found.event",
    "message": "Event not found",
    "request_id": "0f8969a6-0968-4d7c-9cbb-de379e8c19c4"
  }
}

All codes are listed on the errors page.

Try it

Runs a live request from your browser. Pre-filled with the shared demo key (5 requests per second for everyone); paste your own key for steadier results.

Request URLX-API-Keyslug*path

HTTP: —Time: —Rows: —Remaining this second: —Request: —

Press Send to run this request.

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One key gives you Kalshi and Polymarket events, prices with freshness, price history, cross-venue gaps and the live quotes WebSocket.

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