{
  "schemaVersion": "vultax-public-research-data-v1",
  "articleUrl": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026",
  "datasets": [
    {
      "title": "The most-traded midterm contracts, side by side",
      "columns": [
        {
          "name": "Contract",
          "unit": null
        },
        {
          "name": "Kalshi bid / ask",
          "unit": null
        },
        {
          "name": "Polymarket bid / ask",
          "unit": null
        },
        {
          "name": "Median gap, 30 days",
          "unit": null
        },
        {
          "name": "Kalshi open interest",
          "unit": null
        },
        {
          "name": "Polymarket volume",
          "unit": null
        }
      ],
      "rows": [
        [
          "House control — Democrats",
          "85 / 86¢",
          "86 / 87¢",
          "+2.5 pts",
          "7.26M contracts",
          "$6.29M"
        ],
        [
          "House control — Republicans",
          "14 / 15¢",
          "13 / 14¢",
          "−2.5 pts",
          "12.38M contracts",
          "$4.67M"
        ],
        [
          "Senate control — Democrats",
          "48 / 49¢",
          "52 / 53¢",
          "+3.5 pts",
          "1.75M contracts",
          "$2.54M"
        ],
        [
          "Senate control — Republicans",
          "51 / 52¢",
          "48 / 49¢",
          "−3.5 pts",
          "2.65M contracts",
          "$1.76M"
        ],
        [
          "Texas — Talarico (D)",
          "50 / 51¢",
          "51 / 52¢",
          "+1.5 pts",
          "3.14M contracts",
          "$489K"
        ],
        [
          "Texas — Paxton (R)",
          "49 / 51¢",
          "48 / 49¢",
          "−2.5 pts",
          "4.48M contracts",
          "$580K"
        ],
        [
          "Maine — Jackson (D)",
          "66 / 67¢",
          "70 / 71¢",
          "+2.5 pts",
          "1.10M contracts",
          "$803K"
        ],
        [
          "Maine — Collins (R)",
          "33 / 34¢",
          "29 / 30¢",
          "−2.5 pts",
          "1.67M contracts",
          "$537K"
        ],
        [
          "Michigan — El-Sayed (D)",
          "62 / 63¢",
          "62 / 63¢",
          "+1.5 pts",
          "0.94M contracts",
          "$391K"
        ],
        [
          "Michigan — Rogers (R)",
          "38 / 39¢",
          "36 / 38¢",
          "−1.5 pts",
          "1.51M contracts",
          "$318K"
        ],
        [
          "Ohio — Brown (D)",
          "52 / 53¢",
          "51 / 52¢",
          "+1.5 pts",
          "1.09M contracts",
          "$172K"
        ],
        [
          "Ohio — Husted (R)",
          "47 / 48¢",
          "48 / 49¢",
          "−2.0 pts",
          "1.08M contracts",
          "$138K"
        ],
        [
          "North Carolina — Cooper (D)",
          "91.1 / 91.9¢",
          "92 / 93¢",
          "+0.2 pts",
          "1.18M contracts",
          "$45K"
        ],
        [
          "Iowa — Turek (D)",
          "38 / 40¢",
          "38 / 40¢",
          "−1.5 pts",
          "0.89M contracts",
          "$134K"
        ],
        [
          "Iowa — Hinson (R)",
          "61 / 62¢",
          "60 / 62¢",
          "+1.0 pts",
          "0.68M contracts",
          "$138K"
        ]
      ],
      "measurementContext": "Quotes read 18:52 UTC (Kalshi) and 18:53 UTC (Polymarket), 12 September 2026. Kalshi open interest counts contracts that pay $1; Polymarket volume is lifetime dollars traded. Polymarket prices are from its international exchange, which U.S. traders cannot use.",
      "sources": [
        {
          "label": "Kalshi public trade API — events and markets",
          "url": "https://api.elections.kalshi.com/trade-api/v2/events?series_ticker=CONTROLS&with_nested_markets=true",
          "note": "Quotes, open interest and rule text read 18:52 UTC, 12 September 2026; order books every 30 minutes, 12–13 September 2026"
        },
        {
          "label": "Kalshi public trade API — daily candlesticks",
          "url": "https://api.elections.kalshi.com/trade-api/v2/series/CONTROLS/markets/CONTROLS-2026-D/candlesticks?period_interval=1440",
          "note": "Daily closes used for the gap history"
        },
        {
          "label": "Polymarket — Which party will win the Senate in 2026?",
          "url": "https://gamma-api.polymarket.com/events/slug/which-party-will-win-the-senate-in-2026",
          "note": "Quotes and full resolution rules, read 18:53 UTC, 12 September 2026"
        },
        {
          "label": "Polymarket CLOB — price history",
          "url": "https://clob.polymarket.com/prices-history?market=113287701564209339913693347405685749986285999146352375265161592243948562084773&interval=max&fidelity=1440",
          "note": "Daily price points used for the gap history"
        },
        {
          "label": "Polymarket CLOB — order books",
          "url": "https://clob.polymarket.com/books",
          "note": "Midterm contract books, 12–13 September 2026"
        },
        {
          "label": "Polymarket — trading fees",
          "url": "https://docs.polymarket.com/trading/fees",
          "note": "Politics rate 0.04; makers pay nothing; read 2026-09-12"
        },
        {
          "label": "Kalshi — fee rounding",
          "url": "https://docs.kalshi.com/getting_started/fee_rounding",
          "note": "Trade fees are rounded up per fill"
        },
        {
          "label": "OddsShopper — Kalshi fees",
          "url": "https://www.oddsshopper.com/articles/prediction-markets/kalshi-fees",
          "note": "Third-party statement of the 0.07 taker coefficient; Kalshi's own schedule could not be retrieved"
        },
        {
          "label": "Vultax: Kalshi vs Polymarket",
          "url": "https://vultax.com/research/kalshi-polymarket-open-interest-by-category",
          "note": "The venues compared: structure, fees and open interest"
        },
        {
          "label": "Vultax: Kalshi–Polymarket arbitrage after fees",
          "url": "https://vultax.com/research/kalshi-polymarket-arbitrage-gaps-after-fees",
          "note": "How often a midterm gap cleared both venues' fees, and what it returned"
        },
        {
          "label": "Vultax: Is Polymarket legal in the US?",
          "url": "https://vultax.com/research/is-polymarket-legal-in-the-us-2026",
          "note": "Which Polymarket U.S. residents can use"
        }
      ],
      "measurement": {
        "kind": "observed",
        "temporalCoverage": "2026-08-13/2026-09-12",
        "population": "15 of 65 matched midterm contract pairs",
        "methodology": "Best bid and ask from each venue's public API; gap is the median over 30 days of Polymarket's daily price minus Kalshi's daily closing price."
      },
      "id": "side-by-side-table",
      "kind": "published-table",
      "description": "Vultax matched 65 midterm contracts across Polymarket and Kalshi. The venues usually sit 1 to 3 points apart, Polymarket prices Democrats higher in 15 of the 18 most-traded outcomes, and $50,000 on a Democratic Senate cost 1.0¢ above the price on Kalshi and 2.4¢ on Polymarket.",
      "articleUrl": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026",
      "sectionUrl": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026#side-by-side",
      "publishedAt": "2026-09-16",
      "modifiedAt": "2026-09-16",
      "version": "5e3685ed73b83e6503a62952850b276ea3a99834604991dc20a95cf9123da270",
      "isLive": false,
      "limitations": "Published research snapshots and calculations; these exports do not contain current quotes or live account data. Observation windows and populations are stated in the source captions and methodology. Missing metadata is unknown, not zero. Prices and order books were read from public venue data on 12 and 13 September 2026 and change continuously. Gap histories compare daily prices taken at different times of day. Price-impact figures exclude fees and assume no reaction from other traders. Not a forecast, a recommendation to trade, or financial advice.",
      "downloads": {
        "json": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026/data.json?dataset=side-by-side-table",
        "csv": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026/data.csv?dataset=side-by-side-table"
      }
    },
    {
      "title": "Senate control: the price of a Democratic majority on each venue",
      "columns": [
        {
          "name": "Category",
          "unit": null
        },
        {
          "name": "Polymarket",
          "unit": "¢"
        },
        {
          "name": "Kalshi",
          "unit": "¢"
        }
      ],
      "rows": [
        [
          "Jun 29",
          42.5,
          41
        ],
        [
          "Jun 30",
          41.5,
          42
        ],
        [
          "Jul 1",
          41.5,
          41
        ],
        [
          "Jul 2",
          41.5,
          41
        ],
        [
          "Jul 3",
          44.5,
          40
        ],
        [
          "Jul 4",
          44.5,
          41
        ],
        [
          "Jul 5",
          44.5,
          40
        ],
        [
          "Jul 6",
          44.5,
          40
        ],
        [
          "Jul 7",
          45.5,
          42
        ],
        [
          "Jul 8",
          45.5,
          42
        ],
        [
          "Jul 9",
          46.5,
          44
        ],
        [
          "Jul 10",
          46.5,
          43
        ],
        [
          "Jul 11",
          45.5,
          43
        ],
        [
          "Jul 12",
          46.5,
          43
        ],
        [
          "Jul 13",
          45.5,
          44
        ],
        [
          "Jul 14",
          45.5,
          44
        ],
        [
          "Jul 15",
          45.5,
          46
        ],
        [
          "Jul 16",
          45.5,
          45
        ],
        [
          "Jul 17",
          45.5,
          45
        ],
        [
          "Jul 18",
          44.5,
          43
        ],
        [
          "Jul 19",
          43.5,
          44
        ],
        [
          "Jul 20",
          43.5,
          45
        ],
        [
          "Jul 21",
          43.5,
          44
        ],
        [
          "Jul 22",
          43.5,
          44
        ],
        [
          "Jul 23",
          43.5,
          44
        ],
        [
          "Jul 24",
          43.5,
          44
        ],
        [
          "Jul 25",
          43.5,
          44
        ],
        [
          "Jul 26",
          43.5,
          45
        ],
        [
          "Jul 27",
          43.5,
          45
        ],
        [
          "Jul 28",
          43.5,
          44
        ],
        [
          "Jul 30",
          43.5,
          45
        ],
        [
          "Jul 31",
          43.5,
          46
        ],
        [
          "Aug 1",
          43.5,
          47
        ],
        [
          "Aug 2",
          44.5,
          46
        ],
        [
          "Aug 3",
          44.5,
          46
        ],
        [
          "Aug 4",
          44.5,
          47
        ],
        [
          "Aug 5",
          44.5,
          47
        ],
        [
          "Aug 6",
          44.5,
          44
        ],
        [
          "Aug 7",
          45.5,
          47
        ],
        [
          "Aug 8",
          45.5,
          46
        ],
        [
          "Aug 9",
          45.5,
          46
        ],
        [
          "Aug 10",
          45.5,
          46
        ],
        [
          "Aug 11",
          46.5,
          46
        ],
        [
          "Aug 12",
          50.5,
          49
        ],
        [
          "Aug 13",
          52.5,
          49
        ],
        [
          "Aug 14",
          52.5,
          50
        ],
        [
          "Aug 15",
          52.5,
          48
        ],
        [
          "Aug 16",
          52.5,
          49
        ],
        [
          "Aug 17",
          52.5,
          48
        ],
        [
          "Aug 18",
          50.5,
          49
        ],
        [
          "Aug 19",
          51.5,
          48
        ],
        [
          "Aug 20",
          50.5,
          46
        ],
        [
          "Aug 21",
          50.5,
          46
        ],
        [
          "Aug 22",
          50.5,
          47
        ],
        [
          "Aug 23",
          50.5,
          46
        ],
        [
          "Aug 24",
          49.5,
          46
        ],
        [
          "Aug 25",
          49.5,
          46
        ],
        [
          "Aug 26",
          49.5,
          48
        ],
        [
          "Aug 27",
          50.5,
          49
        ],
        [
          "Aug 28",
          50.5,
          48
        ],
        [
          "Aug 29",
          50.5,
          48
        ],
        [
          "Aug 30",
          50.5,
          48
        ],
        [
          "Aug 31",
          50.5,
          48
        ],
        [
          "Sep 1",
          50.5,
          49
        ],
        [
          "Sep 2",
          50.5,
          48
        ],
        [
          "Sep 3",
          51.5,
          48
        ],
        [
          "Sep 4",
          51.5,
          48
        ],
        [
          "Sep 5",
          51.5,
          48
        ],
        [
          "Sep 6",
          51.5,
          47
        ],
        [
          "Sep 7",
          51.5,
          48
        ],
        [
          "Sep 8",
          51.5,
          47
        ],
        [
          "Sep 9",
          52.5,
          48
        ],
        [
          "Sep 10",
          52.5,
          47
        ],
        [
          "Sep 11",
          52.5,
          48
        ],
        [
          "Sep 12",
          52.5,
          49
        ]
      ],
      "measurementContext": "Daily price in cents, 29 Jun to 12 Sep 2026. Polymarket daily price; Kalshi daily close.",
      "sources": [
        {
          "label": "Kalshi public trade API — events and markets",
          "url": "https://api.elections.kalshi.com/trade-api/v2/events?series_ticker=CONTROLS&with_nested_markets=true",
          "note": "Quotes, open interest and rule text read 18:52 UTC, 12 September 2026; order books every 30 minutes, 12–13 September 2026"
        },
        {
          "label": "Kalshi public trade API — daily candlesticks",
          "url": "https://api.elections.kalshi.com/trade-api/v2/series/CONTROLS/markets/CONTROLS-2026-D/candlesticks?period_interval=1440",
          "note": "Daily closes used for the gap history"
        },
        {
          "label": "Polymarket — Which party will win the Senate in 2026?",
          "url": "https://gamma-api.polymarket.com/events/slug/which-party-will-win-the-senate-in-2026",
          "note": "Quotes and full resolution rules, read 18:53 UTC, 12 September 2026"
        },
        {
          "label": "Polymarket CLOB — price history",
          "url": "https://clob.polymarket.com/prices-history?market=113287701564209339913693347405685749986285999146352375265161592243948562084773&interval=max&fidelity=1440",
          "note": "Daily price points used for the gap history"
        },
        {
          "label": "Polymarket CLOB — order books",
          "url": "https://clob.polymarket.com/books",
          "note": "Midterm contract books, 12–13 September 2026"
        },
        {
          "label": "Polymarket — trading fees",
          "url": "https://docs.polymarket.com/trading/fees",
          "note": "Politics rate 0.04; makers pay nothing; read 2026-09-12"
        },
        {
          "label": "Kalshi — fee rounding",
          "url": "https://docs.kalshi.com/getting_started/fee_rounding",
          "note": "Trade fees are rounded up per fill"
        },
        {
          "label": "OddsShopper — Kalshi fees",
          "url": "https://www.oddsshopper.com/articles/prediction-markets/kalshi-fees",
          "note": "Third-party statement of the 0.07 taker coefficient; Kalshi's own schedule could not be retrieved"
        },
        {
          "label": "Vultax: Kalshi vs Polymarket",
          "url": "https://vultax.com/research/kalshi-polymarket-open-interest-by-category",
          "note": "The venues compared: structure, fees and open interest"
        },
        {
          "label": "Vultax: Kalshi–Polymarket arbitrage after fees",
          "url": "https://vultax.com/research/kalshi-polymarket-arbitrage-gaps-after-fees",
          "note": "How often a midterm gap cleared both venues' fees, and what it returned"
        },
        {
          "label": "Vultax: Is Polymarket legal in the US?",
          "url": "https://vultax.com/research/is-polymarket-legal-in-the-us-2026",
          "note": "Which Polymarket U.S. residents can use"
        }
      ],
      "measurement": {
        "kind": "observed",
        "temporalCoverage": "2026-06-29/2026-09-12",
        "population": "Polymarket \"Which party will win the Senate in 2026?\" Democratic Party market and Kalshi CONTROLS-2026-D",
        "methodology": "Polymarket CLOB daily price history and Kalshi daily candlestick close, aligned by UTC date; 29 July missing from Kalshi's series."
      },
      "id": "direction-chart",
      "kind": "published-chart",
      "description": "Vultax matched 65 midterm contracts across Polymarket and Kalshi. The venues usually sit 1 to 3 points apart, Polymarket prices Democrats higher in 15 of the 18 most-traded outcomes, and $50,000 on a Democratic Senate cost 1.0¢ above the price on Kalshi and 2.4¢ on Polymarket.",
      "articleUrl": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026",
      "sectionUrl": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026#direction",
      "publishedAt": "2026-09-16",
      "modifiedAt": "2026-09-16",
      "version": "85dffe44ae6231e8f298bc0887f9840b1667ff3900e8694d0b45db8c44fa7cd7",
      "isLive": false,
      "limitations": "Published research snapshots and calculations; these exports do not contain current quotes or live account data. Observation windows and populations are stated in the source captions and methodology. Missing metadata is unknown, not zero. Prices and order books were read from public venue data on 12 and 13 September 2026 and change continuously. Gap histories compare daily prices taken at different times of day. Price-impact figures exclude fees and assume no reaction from other traders. Not a forecast, a recommendation to trade, or financial advice.",
      "downloads": {
        "json": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026/data.json?dataset=direction-chart",
        "csv": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026/data.csv?dataset=direction-chart"
      }
    },
    {
      "title": "Average daily gap between Polymarket and Kalshi, last 30 days",
      "columns": [
        {
          "name": "Category",
          "unit": null
        },
        {
          "name": "Average absolute gap",
          "unit": "pts"
        }
      ],
      "rows": [
        [
          "Senate control",
          3.3
        ],
        [
          "House control",
          3
        ],
        [
          "Maine",
          3
        ],
        [
          "Texas",
          2.2
        ],
        [
          "Michigan",
          1.9
        ],
        [
          "Ohio",
          1.7
        ],
        [
          "Iowa",
          1.6
        ],
        [
          "Georgia",
          1.1
        ],
        [
          "South Carolina",
          0.9
        ],
        [
          "North Carolina",
          0.6
        ]
      ],
      "measurementContext": "Absolute difference in points, 13 Aug to 12 Sep 2026. More heavily traded side of each contract.",
      "sources": [
        {
          "label": "Kalshi public trade API — events and markets",
          "url": "https://api.elections.kalshi.com/trade-api/v2/events?series_ticker=CONTROLS&with_nested_markets=true",
          "note": "Quotes, open interest and rule text read 18:52 UTC, 12 September 2026; order books every 30 minutes, 12–13 September 2026"
        },
        {
          "label": "Kalshi public trade API — daily candlesticks",
          "url": "https://api.elections.kalshi.com/trade-api/v2/series/CONTROLS/markets/CONTROLS-2026-D/candlesticks?period_interval=1440",
          "note": "Daily closes used for the gap history"
        },
        {
          "label": "Polymarket — Which party will win the Senate in 2026?",
          "url": "https://gamma-api.polymarket.com/events/slug/which-party-will-win-the-senate-in-2026",
          "note": "Quotes and full resolution rules, read 18:53 UTC, 12 September 2026"
        },
        {
          "label": "Polymarket CLOB — price history",
          "url": "https://clob.polymarket.com/prices-history?market=113287701564209339913693347405685749986285999146352375265161592243948562084773&interval=max&fidelity=1440",
          "note": "Daily price points used for the gap history"
        },
        {
          "label": "Polymarket CLOB — order books",
          "url": "https://clob.polymarket.com/books",
          "note": "Midterm contract books, 12–13 September 2026"
        },
        {
          "label": "Polymarket — trading fees",
          "url": "https://docs.polymarket.com/trading/fees",
          "note": "Politics rate 0.04; makers pay nothing; read 2026-09-12"
        },
        {
          "label": "Kalshi — fee rounding",
          "url": "https://docs.kalshi.com/getting_started/fee_rounding",
          "note": "Trade fees are rounded up per fill"
        },
        {
          "label": "OddsShopper — Kalshi fees",
          "url": "https://www.oddsshopper.com/articles/prediction-markets/kalshi-fees",
          "note": "Third-party statement of the 0.07 taker coefficient; Kalshi's own schedule could not be retrieved"
        },
        {
          "label": "Vultax: Kalshi vs Polymarket",
          "url": "https://vultax.com/research/kalshi-polymarket-open-interest-by-category",
          "note": "The venues compared: structure, fees and open interest"
        },
        {
          "label": "Vultax: Kalshi–Polymarket arbitrage after fees",
          "url": "https://vultax.com/research/kalshi-polymarket-arbitrage-gaps-after-fees",
          "note": "How often a midterm gap cleared both venues' fees, and what it returned"
        },
        {
          "label": "Vultax: Is Polymarket legal in the US?",
          "url": "https://vultax.com/research/is-polymarket-legal-in-the-us-2026",
          "note": "Which Polymarket U.S. residents can use"
        }
      ],
      "measurement": {
        "kind": "observed",
        "temporalCoverage": "2026-08-13/2026-09-12",
        "population": "10 matched contracts with the largest Kalshi open interest per race",
        "methodology": "Mean of |Polymarket daily price − Kalshi daily close| in points over the days both venues had a price."
      },
      "id": "gap-size-chart",
      "kind": "published-chart",
      "description": "Vultax matched 65 midterm contracts across Polymarket and Kalshi. The venues usually sit 1 to 3 points apart, Polymarket prices Democrats higher in 15 of the 18 most-traded outcomes, and $50,000 on a Democratic Senate cost 1.0¢ above the price on Kalshi and 2.4¢ on Polymarket.",
      "articleUrl": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026",
      "sectionUrl": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026#gap-size",
      "publishedAt": "2026-09-16",
      "modifiedAt": "2026-09-16",
      "version": "e5e7f933ab4bcd2da3bb490ead05e582a3b8644aaf69421604954539e6af7e2f",
      "isLive": false,
      "limitations": "Published research snapshots and calculations; these exports do not contain current quotes or live account data. Observation windows and populations are stated in the source captions and methodology. Missing metadata is unknown, not zero. Prices and order books were read from public venue data on 12 and 13 September 2026 and change continuously. Gap histories compare daily prices taken at different times of day. Price-impact figures exclude fees and assume no reaction from other traders. Not a forecast, a recommendation to trade, or financial advice.",
      "downloads": {
        "json": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026/data.json?dataset=gap-size-chart",
        "csv": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026/data.csv?dataset=gap-size-chart"
      }
    },
    {
      "title": "The contracts are not written the same way",
      "columns": [
        {
          "name": "",
          "unit": null
        },
        {
          "name": "Kalshi",
          "unit": null
        },
        {
          "name": "Polymarket",
          "unit": null
        }
      ],
      "rows": [
        [
          "Chamber control",
          "Pays if the party \"has won control\"; may be settled early on a consensus of media calls, otherwise by the party of the Speaker (House) or President pro tempore (Senate) on 1 February 2027",
          "Counts seats: a majority of voting seats, or half plus the Vice Presidency; independents count with the party they caucus with or announce they will; may stay open until 4 January if caucus intentions are unclear"
        ],
        [
          "Senate races",
          "Markets carry a candidate's name but pay if \"a representative of the Republican party\" (or Democratic) \"is sworn in\" for the term beginning in 2027; early settlement on media consensus is allowed",
          "Pays the winner of the 2026 election including any runoff, once the Associated Press, Fox News and NBC all call it; independents do not count as a party's candidate"
        ],
        [
          "Which election",
          "Also lists contracts for the Senate term beginning in 2029 in the same state series",
          "Lists 2026 races under \"Senate Election Winner\""
        ]
      ],
      "measurementContext": "Rule text read from each venue's public market data on 12 September 2026. Kalshi's full rules are longer than the summaries its API returns.",
      "sources": [
        {
          "label": "Kalshi public trade API — events and markets",
          "url": "https://api.elections.kalshi.com/trade-api/v2/events?series_ticker=CONTROLS&with_nested_markets=true",
          "note": "Quotes, open interest and rule text read 18:52 UTC, 12 September 2026; order books every 30 minutes, 12–13 September 2026"
        },
        {
          "label": "Kalshi public trade API — daily candlesticks",
          "url": "https://api.elections.kalshi.com/trade-api/v2/series/CONTROLS/markets/CONTROLS-2026-D/candlesticks?period_interval=1440",
          "note": "Daily closes used for the gap history"
        },
        {
          "label": "Polymarket — Which party will win the Senate in 2026?",
          "url": "https://gamma-api.polymarket.com/events/slug/which-party-will-win-the-senate-in-2026",
          "note": "Quotes and full resolution rules, read 18:53 UTC, 12 September 2026"
        },
        {
          "label": "Polymarket CLOB — price history",
          "url": "https://clob.polymarket.com/prices-history?market=113287701564209339913693347405685749986285999146352375265161592243948562084773&interval=max&fidelity=1440",
          "note": "Daily price points used for the gap history"
        },
        {
          "label": "Polymarket CLOB — order books",
          "url": "https://clob.polymarket.com/books",
          "note": "Midterm contract books, 12–13 September 2026"
        },
        {
          "label": "Polymarket — trading fees",
          "url": "https://docs.polymarket.com/trading/fees",
          "note": "Politics rate 0.04; makers pay nothing; read 2026-09-12"
        },
        {
          "label": "Kalshi — fee rounding",
          "url": "https://docs.kalshi.com/getting_started/fee_rounding",
          "note": "Trade fees are rounded up per fill"
        },
        {
          "label": "OddsShopper — Kalshi fees",
          "url": "https://www.oddsshopper.com/articles/prediction-markets/kalshi-fees",
          "note": "Third-party statement of the 0.07 taker coefficient; Kalshi's own schedule could not be retrieved"
        },
        {
          "label": "Vultax: Kalshi vs Polymarket",
          "url": "https://vultax.com/research/kalshi-polymarket-open-interest-by-category",
          "note": "The venues compared: structure, fees and open interest"
        },
        {
          "label": "Vultax: Kalshi–Polymarket arbitrage after fees",
          "url": "https://vultax.com/research/kalshi-polymarket-arbitrage-gaps-after-fees",
          "note": "How often a midterm gap cleared both venues' fees, and what it returned"
        },
        {
          "label": "Vultax: Is Polymarket legal in the US?",
          "url": "https://vultax.com/research/is-polymarket-legal-in-the-us-2026",
          "note": "Which Polymarket U.S. residents can use"
        }
      ],
      "measurement": {
        "kind": "reference",
        "temporalCoverage": "2026-09-12",
        "population": null,
        "methodology": "Quoted from Kalshi rules_primary and rules_secondary fields and Polymarket market descriptions."
      },
      "id": "rules-table",
      "kind": "published-table",
      "description": "Vultax matched 65 midterm contracts across Polymarket and Kalshi. The venues usually sit 1 to 3 points apart, Polymarket prices Democrats higher in 15 of the 18 most-traded outcomes, and $50,000 on a Democratic Senate cost 1.0¢ above the price on Kalshi and 2.4¢ on Polymarket.",
      "articleUrl": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026",
      "sectionUrl": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026#rules",
      "publishedAt": "2026-09-16",
      "modifiedAt": "2026-09-16",
      "version": "0adb7c2cda6de1e728dae4af52d1b81396e9687a38867c786c688d04e5fa8075",
      "isLive": false,
      "limitations": "Published research snapshots and calculations; these exports do not contain current quotes or live account data. Observation windows and populations are stated in the source captions and methodology. Missing metadata is unknown, not zero. Prices and order books were read from public venue data on 12 and 13 September 2026 and change continuously. Gap histories compare daily prices taken at different times of day. Price-impact figures exclude fees and assume no reaction from other traders. Not a forecast, a recommendation to trade, or financial advice.",
      "downloads": {
        "json": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026/data.json?dataset=rules-table",
        "csv": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026/data.csv?dataset=rules-table"
      }
    },
    {
      "title": "The contracts people watch",
      "columns": [
        {
          "name": "Contract",
          "unit": null
        },
        {
          "name": "Price, Kalshi / Polymarket",
          "unit": null
        },
        {
          "name": "$10,000 buy above the price",
          "unit": null
        },
        {
          "name": "$50,000 buy above the price",
          "unit": null
        },
        {
          "name": "Readings where $50,000 filled",
          "unit": null
        }
      ],
      "rows": [
        [
          "House control — Democrats",
          "85.5¢ / 86.5¢",
          "0.5¢ / 0.5¢",
          "0.5¢ / 1.3¢",
          "100% / 100%"
        ],
        [
          "House control — Republicans",
          "14.5¢ / 13.5¢",
          "0.5¢ / 1.1¢",
          "1.3¢ / 1.4¢",
          "100% / 98%"
        ],
        [
          "Senate control — Democrats",
          "48.5¢ / 53.5¢",
          "0.5¢ / 0.8¢",
          "1.0¢ / 2.4¢",
          "100% / 100%"
        ],
        [
          "Senate control — Republicans",
          "51.5¢ / 47.5¢",
          "0.5¢ / 0.9¢",
          "0.8¢ / 2.6¢",
          "100% / 100%"
        ],
        [
          "Texas — Talarico (D)",
          "50.5¢ / 51.5¢",
          "0.5¢ / 2.2¢",
          "0.8¢ / 6.6¢",
          "100% / 16%"
        ],
        [
          "Texas — Paxton (R)",
          "50.5¢ / 48.5¢",
          "1.0¢ / 1.8¢",
          "3.7¢ / 6.0¢",
          "100% / 78%"
        ],
        [
          "Ohio — Brown (D)",
          "52.5¢ / 51.5¢",
          "1.0¢ / 0.7¢",
          "5.0¢ / 20.5¢",
          "21% / 45%"
        ],
        [
          "Ohio — Husted (R)",
          "47.5¢ / 48.5¢",
          "0.6¢ / 1.1¢",
          "— / 6.9¢",
          "0% / 100%"
        ],
        [
          "Maine — Jackson (D)",
          "66.5¢ / 70.5¢",
          "1.1¢ / 1.0¢",
          "5.6¢ / 5.9¢",
          "100% / 100%"
        ],
        [
          "Maine — Collins (R)",
          "33.5¢ / 29.5¢",
          "2.2¢ / 0.8¢",
          "— / —",
          "0% / 0%"
        ],
        [
          "Michigan — El-Sayed (D)",
          "61.5¢ / 62.5¢",
          "0.5¢ / 2.4¢",
          "1.7¢ / 7.5¢",
          "100% / 100%"
        ],
        [
          "Michigan — Rogers (R)",
          "38.5¢ / 36.5¢",
          "2.0¢ / 3.0¢",
          "5.9¢ / 8.7¢",
          "100% / 34%"
        ],
        [
          "North Carolina — Cooper (D)",
          "91.5¢ / 92.5¢",
          "0.8¢ / 1.4¢",
          "1.9¢ / 4.6¢",
          "100% / 100%"
        ],
        [
          "Georgia — Ossoff (D)",
          "92.5¢ / 92.5¢",
          "0.8¢ / 2.4¢",
          "1.7¢ / 5.2¢",
          "100% / 100%"
        ],
        [
          "Iowa — Turek (D)",
          "38.5¢ / 39.5¢",
          "1.4¢ / 10.3¢",
          "10.4¢ / 43.0¢",
          "95% / 66%"
        ],
        [
          "Iowa — Hinson (R)",
          "61.5¢ / 60.5¢",
          "1.4¢ / 1.7¢",
          "— / 13.7¢",
          "0% / 100%"
        ]
      ],
      "measurementContext": "58 readings every 30 minutes, 18:51 UTC 12 September to 23:21 UTC 13 September 2026. Cost above the price is the average price paid for Yes minus the midpoint, median over readings where the order filled within the 20 price levels read; a dash means it never filled. Fees excluded. Polymarket prices are from its international exchange.",
      "sources": [
        {
          "label": "Kalshi public trade API — events and markets",
          "url": "https://api.elections.kalshi.com/trade-api/v2/events?series_ticker=CONTROLS&with_nested_markets=true",
          "note": "Quotes, open interest and rule text read 18:52 UTC, 12 September 2026; order books every 30 minutes, 12–13 September 2026"
        },
        {
          "label": "Kalshi public trade API — daily candlesticks",
          "url": "https://api.elections.kalshi.com/trade-api/v2/series/CONTROLS/markets/CONTROLS-2026-D/candlesticks?period_interval=1440",
          "note": "Daily closes used for the gap history"
        },
        {
          "label": "Polymarket — Which party will win the Senate in 2026?",
          "url": "https://gamma-api.polymarket.com/events/slug/which-party-will-win-the-senate-in-2026",
          "note": "Quotes and full resolution rules, read 18:53 UTC, 12 September 2026"
        },
        {
          "label": "Polymarket CLOB — price history",
          "url": "https://clob.polymarket.com/prices-history?market=113287701564209339913693347405685749986285999146352375265161592243948562084773&interval=max&fidelity=1440",
          "note": "Daily price points used for the gap history"
        },
        {
          "label": "Polymarket CLOB — order books",
          "url": "https://clob.polymarket.com/books",
          "note": "Midterm contract books, 12–13 September 2026"
        },
        {
          "label": "Polymarket — trading fees",
          "url": "https://docs.polymarket.com/trading/fees",
          "note": "Politics rate 0.04; makers pay nothing; read 2026-09-12"
        },
        {
          "label": "Kalshi — fee rounding",
          "url": "https://docs.kalshi.com/getting_started/fee_rounding",
          "note": "Trade fees are rounded up per fill"
        },
        {
          "label": "OddsShopper — Kalshi fees",
          "url": "https://www.oddsshopper.com/articles/prediction-markets/kalshi-fees",
          "note": "Third-party statement of the 0.07 taker coefficient; Kalshi's own schedule could not be retrieved"
        },
        {
          "label": "Vultax: Kalshi vs Polymarket",
          "url": "https://vultax.com/research/kalshi-polymarket-open-interest-by-category",
          "note": "The venues compared: structure, fees and open interest"
        },
        {
          "label": "Vultax: Kalshi–Polymarket arbitrage after fees",
          "url": "https://vultax.com/research/kalshi-polymarket-arbitrage-gaps-after-fees",
          "note": "How often a midterm gap cleared both venues' fees, and what it returned"
        },
        {
          "label": "Vultax: Is Polymarket legal in the US?",
          "url": "https://vultax.com/research/is-polymarket-legal-in-the-us-2026",
          "note": "Which Polymarket U.S. residents can use"
        }
      ],
      "measurement": {
        "kind": "observed",
        "temporalCoverage": "2026-09-12T18:51Z/2026-09-13T23:21Z",
        "population": "16 of 65 matched midterm contracts",
        "methodology": "Buy of Yes filled level by level against each venue's asks to the stated dollar amount; average fill price minus the midpoint."
      },
      "id": "big-contracts-table",
      "kind": "published-table",
      "description": "Vultax matched 65 midterm contracts across Polymarket and Kalshi. The venues usually sit 1 to 3 points apart, Polymarket prices Democrats higher in 15 of the 18 most-traded outcomes, and $50,000 on a Democratic Senate cost 1.0¢ above the price on Kalshi and 2.4¢ on Polymarket.",
      "articleUrl": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026",
      "sectionUrl": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026#big-contracts",
      "publishedAt": "2026-09-16",
      "modifiedAt": "2026-09-16",
      "version": "b57d9dd29a32f75e14e1a0657e9d2fac97ab2a0211c054d682e3079f47362258",
      "isLive": false,
      "limitations": "Published research snapshots and calculations; these exports do not contain current quotes or live account data. Observation windows and populations are stated in the source captions and methodology. Missing metadata is unknown, not zero. Prices and order books were read from public venue data on 12 and 13 September 2026 and change continuously. Gap histories compare daily prices taken at different times of day. Price-impact figures exclude fees and assume no reaction from other traders. Not a forecast, a recommendation to trade, or financial advice.",
      "downloads": {
        "json": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026/data.json?dataset=big-contracts-table",
        "csv": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026/data.csv?dataset=big-contracts-table"
      }
    },
    {
      "title": "What a $50,000 buy costs above the price",
      "columns": [
        {
          "name": "Category",
          "unit": null
        },
        {
          "name": "Kalshi",
          "unit": "¢"
        },
        {
          "name": "Polymarket",
          "unit": "¢"
        }
      ],
      "rows": [
        [
          "House D",
          0.5,
          1.3
        ],
        [
          "House R",
          1.3,
          1.4
        ],
        [
          "Senate D",
          1,
          2.4
        ],
        [
          "Senate R",
          0.8,
          2.6
        ],
        [
          "Maine",
          5.6,
          5.9
        ],
        [
          "N. Carolina",
          1.9,
          4.6
        ],
        [
          "Georgia",
          1.7,
          5.2
        ],
        [
          "Michigan",
          1.7,
          7.5
        ]
      ],
      "measurementContext": "Cents per contract, median over 58 readings. The eight contracts where the order filled in at least 90% of readings on both venues: House and Senate control by party, and the Democratic candidates in Maine, North Carolina, Georgia and Michigan.",
      "sources": [
        {
          "label": "Kalshi public trade API — events and markets",
          "url": "https://api.elections.kalshi.com/trade-api/v2/events?series_ticker=CONTROLS&with_nested_markets=true",
          "note": "Quotes, open interest and rule text read 18:52 UTC, 12 September 2026; order books every 30 minutes, 12–13 September 2026"
        },
        {
          "label": "Kalshi public trade API — daily candlesticks",
          "url": "https://api.elections.kalshi.com/trade-api/v2/series/CONTROLS/markets/CONTROLS-2026-D/candlesticks?period_interval=1440",
          "note": "Daily closes used for the gap history"
        },
        {
          "label": "Polymarket — Which party will win the Senate in 2026?",
          "url": "https://gamma-api.polymarket.com/events/slug/which-party-will-win-the-senate-in-2026",
          "note": "Quotes and full resolution rules, read 18:53 UTC, 12 September 2026"
        },
        {
          "label": "Polymarket CLOB — price history",
          "url": "https://clob.polymarket.com/prices-history?market=113287701564209339913693347405685749986285999146352375265161592243948562084773&interval=max&fidelity=1440",
          "note": "Daily price points used for the gap history"
        },
        {
          "label": "Polymarket CLOB — order books",
          "url": "https://clob.polymarket.com/books",
          "note": "Midterm contract books, 12–13 September 2026"
        },
        {
          "label": "Polymarket — trading fees",
          "url": "https://docs.polymarket.com/trading/fees",
          "note": "Politics rate 0.04; makers pay nothing; read 2026-09-12"
        },
        {
          "label": "Kalshi — fee rounding",
          "url": "https://docs.kalshi.com/getting_started/fee_rounding",
          "note": "Trade fees are rounded up per fill"
        },
        {
          "label": "OddsShopper — Kalshi fees",
          "url": "https://www.oddsshopper.com/articles/prediction-markets/kalshi-fees",
          "note": "Third-party statement of the 0.07 taker coefficient; Kalshi's own schedule could not be retrieved"
        },
        {
          "label": "Vultax: Kalshi vs Polymarket",
          "url": "https://vultax.com/research/kalshi-polymarket-open-interest-by-category",
          "note": "The venues compared: structure, fees and open interest"
        },
        {
          "label": "Vultax: Kalshi–Polymarket arbitrage after fees",
          "url": "https://vultax.com/research/kalshi-polymarket-arbitrage-gaps-after-fees",
          "note": "How often a midterm gap cleared both venues' fees, and what it returned"
        },
        {
          "label": "Vultax: Is Polymarket legal in the US?",
          "url": "https://vultax.com/research/is-polymarket-legal-in-the-us-2026",
          "note": "Which Polymarket U.S. residents can use"
        }
      ],
      "measurement": {
        "kind": "observed",
        "temporalCoverage": "2026-09-12T18:51Z/2026-09-13T23:21Z",
        "population": "8 of 65 matched midterm contracts where a $50,000 buy filled in at least 90% of readings on both venues",
        "methodology": "Buy of Yes filled level by level against each venue's asks to $50,000; average fill price minus the midpoint, median over the readings where it filled. Fees excluded."
      },
      "id": "big-contracts-chart",
      "kind": "published-chart",
      "description": "Vultax matched 65 midterm contracts across Polymarket and Kalshi. The venues usually sit 1 to 3 points apart, Polymarket prices Democrats higher in 15 of the 18 most-traded outcomes, and $50,000 on a Democratic Senate cost 1.0¢ above the price on Kalshi and 2.4¢ on Polymarket.",
      "articleUrl": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026",
      "sectionUrl": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026#big-contracts",
      "publishedAt": "2026-09-16",
      "modifiedAt": "2026-09-16",
      "version": "2cb580f0cb1e26a289b8a7b39bc1c38a650f4da1e299f2759cf5ff5c4503a6a5",
      "isLive": false,
      "limitations": "Published research snapshots and calculations; these exports do not contain current quotes or live account data. Observation windows and populations are stated in the source captions and methodology. Missing metadata is unknown, not zero. Prices and order books were read from public venue data on 12 and 13 September 2026 and change continuously. Gap histories compare daily prices taken at different times of day. Price-impact figures exclude fees and assume no reaction from other traders. Not a forecast, a recommendation to trade, or financial advice.",
      "downloads": {
        "json": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026/data.json?dataset=big-contracts-chart",
        "csv": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026/data.csv?dataset=big-contracts-chart"
      }
    },
    {
      "title": "Longshots move furthest",
      "columns": [
        {
          "name": "Candidate",
          "unit": null
        },
        {
          "name": "Polymarket price",
          "unit": null
        },
        {
          "name": "$1,000 buy above the price",
          "unit": null
        },
        {
          "name": "$10,000 buy above the price",
          "unit": null
        }
      ],
      "rows": [
        [
          "Todd Achilles (I), Idaho",
          "1.1¢",
          "52.5¢",
          "68.7¢"
        ],
        [
          "Everett Wess (D), Alabama",
          "5.0¢",
          "11.8¢",
          "48.7¢"
        ],
        [
          "Bert Mizusawa (R), Virginia",
          "4.5¢",
          "4.6¢",
          "37.5¢"
        ],
        [
          "Republican nominee, Delaware",
          "4.5¢",
          "4.6¢",
          "36.7¢"
        ],
        [
          "Michele Tafoya (R), Minnesota",
          "8.5¢",
          "2.3¢",
          "35.4¢"
        ],
        [
          "Scott Colom (D), Mississippi",
          "6.5¢",
          "2.6¢",
          "28.4¢"
        ],
        [
          "Michael Whatley (R), North Carolina",
          "8.5¢",
          "1.7¢",
          "24.1¢"
        ]
      ],
      "measurementContext": "Polymarket contracts priced under 10 cents where a $10,000 buy filled in at least 90% of 58 readings, 12–13 September 2026. Medians. On Kalshi, where the same candidate traded, a $10,000 buy of Whatley cost 0.9 cents and of Tafoya 6.0 cents above the price.",
      "sources": [
        {
          "label": "Kalshi public trade API — events and markets",
          "url": "https://api.elections.kalshi.com/trade-api/v2/events?series_ticker=CONTROLS&with_nested_markets=true",
          "note": "Quotes, open interest and rule text read 18:52 UTC, 12 September 2026; order books every 30 minutes, 12–13 September 2026"
        },
        {
          "label": "Kalshi public trade API — daily candlesticks",
          "url": "https://api.elections.kalshi.com/trade-api/v2/series/CONTROLS/markets/CONTROLS-2026-D/candlesticks?period_interval=1440",
          "note": "Daily closes used for the gap history"
        },
        {
          "label": "Polymarket — Which party will win the Senate in 2026?",
          "url": "https://gamma-api.polymarket.com/events/slug/which-party-will-win-the-senate-in-2026",
          "note": "Quotes and full resolution rules, read 18:53 UTC, 12 September 2026"
        },
        {
          "label": "Polymarket CLOB — price history",
          "url": "https://clob.polymarket.com/prices-history?market=113287701564209339913693347405685749986285999146352375265161592243948562084773&interval=max&fidelity=1440",
          "note": "Daily price points used for the gap history"
        },
        {
          "label": "Polymarket CLOB — order books",
          "url": "https://clob.polymarket.com/books",
          "note": "Midterm contract books, 12–13 September 2026"
        },
        {
          "label": "Polymarket — trading fees",
          "url": "https://docs.polymarket.com/trading/fees",
          "note": "Politics rate 0.04; makers pay nothing; read 2026-09-12"
        },
        {
          "label": "Kalshi — fee rounding",
          "url": "https://docs.kalshi.com/getting_started/fee_rounding",
          "note": "Trade fees are rounded up per fill"
        },
        {
          "label": "OddsShopper — Kalshi fees",
          "url": "https://www.oddsshopper.com/articles/prediction-markets/kalshi-fees",
          "note": "Third-party statement of the 0.07 taker coefficient; Kalshi's own schedule could not be retrieved"
        },
        {
          "label": "Vultax: Kalshi vs Polymarket",
          "url": "https://vultax.com/research/kalshi-polymarket-open-interest-by-category",
          "note": "The venues compared: structure, fees and open interest"
        },
        {
          "label": "Vultax: Kalshi–Polymarket arbitrage after fees",
          "url": "https://vultax.com/research/kalshi-polymarket-arbitrage-gaps-after-fees",
          "note": "How often a midterm gap cleared both venues' fees, and what it returned"
        },
        {
          "label": "Vultax: Is Polymarket legal in the US?",
          "url": "https://vultax.com/research/is-polymarket-legal-in-the-us-2026",
          "note": "Which Polymarket U.S. residents can use"
        }
      ],
      "measurement": {
        "kind": "observed",
        "temporalCoverage": "2026-09-12T18:51Z/2026-09-13T23:21Z",
        "population": "7 Polymarket longshot contracts",
        "methodology": "As above, for $1,000 and $10,000 buys of Yes."
      },
      "id": "longshots-table",
      "kind": "published-table",
      "description": "Vultax matched 65 midterm contracts across Polymarket and Kalshi. The venues usually sit 1 to 3 points apart, Polymarket prices Democrats higher in 15 of the 18 most-traded outcomes, and $50,000 on a Democratic Senate cost 1.0¢ above the price on Kalshi and 2.4¢ on Polymarket.",
      "articleUrl": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026",
      "sectionUrl": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026#longshots",
      "publishedAt": "2026-09-16",
      "modifiedAt": "2026-09-16",
      "version": "5ae1e30a72430c374041e57e1c330e2fe6e953093bb86fe2d8715f2b75e9a42d",
      "isLive": false,
      "limitations": "Published research snapshots and calculations; these exports do not contain current quotes or live account data. Observation windows and populations are stated in the source captions and methodology. Missing metadata is unknown, not zero. Prices and order books were read from public venue data on 12 and 13 September 2026 and change continuously. Gap histories compare daily prices taken at different times of day. Price-impact figures exclude fees and assume no reaction from other traders. Not a forecast, a recommendation to trade, or financial advice.",
      "downloads": {
        "json": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026/data.json?dataset=longshots-table",
        "csv": "https://vultax.com/research/polymarket-vs-kalshi-midterms-odds-2026/data.csv?dataset=longshots-table"
      }
    }
  ]
}