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Emitted when outcome tokens (YES + NO shares) are merged back into collateral (USDC) via the Conditional Tokens Framework mergePositions function. The inverse of a position split. Merges are much rarer than splits (~20x less frequent). They happen when a trader holds both YES and NO tokens for a condition and redeems them back to USDC. 
{
  "data": {
    "amount": 1414.0,
    "block_number": 84090704,
    "collateral_token": "0x3a3bd7bb9528e159577f7c2e685cc81a765002e2",
    "condition_id": "0xd1747284d6048b2a3dcfbee489db405f36de18f9590197dd0e5c9f0c246bf050",
    "event_title": "Republican Presidential Nominee 2028",
    "event_type": "position_merge",
    "log_index": 1004,
    "market_image": "https://polymarket-upload.s3.us-east-2.amazonaws.com/Byron_Donalds.png",
    "market_slug": "will-byron-donalds-win-the-2028-republican-presidential-nomination",
    "market_title": "Will Byron Donalds win the 2028 Republican presidential nomination?",
    "neg_risk": true,
    "stakeholder": "0xd91e80cf2e7be2e162c6513ced06f1dd0da35296",
    "taker_base_fee": 0.0,
    "tick_size": 0.001,
    "timestamp": 1773301441000,
    "tokens": {
      "311624663652221737215322113380496984764966764039692273354641152455298576851": "Yes",
      "43292374563904271719486871569114922516560719431752184778538513591321835161630": "No"
    },
    "tx_hash": "0x92fa6de980f6cad9eae9ef28e908d19faa10838a07f01352b0cae63b5f8299fb"
  },
  "timestamp": 1773301441000,
  "type": "position_merge"
}

​
Fields

​
type
string
required
Always "position_merge".
​
timestamp
number
required
Block timestamp in Unix milliseconds.
​
data
object
required

​
Use cases

  • Position unwinding — detect when traders are closing positions by merging outcome tokens
  • Liquidity withdrawal tracking — merges reduce the total supply of outcome tokens in a market
  • Arbitrage detection — merges after buying both outcomes at favorable prices signal arbitrage
Not included in global firehose by default. Subscribe explicitly with event_types: ["position_merge"] or use the wallets/markets subscription types which include it automatically.