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Polymarket Binary Hedging Arbitrage Bot: From Concept to Live Execution (Dual-Leg Lock Strategy)

Polymarket’s short-duration binary markets — especially the popular BTC/ETH 15-minute Up/Down contracts — offer one of the cleanest structural arbitrage opportunities in prediction markets. Because YES + NO prices must sum to 1.00 at resolution, any temporary sum below $1.00 creates a risk-free (or near risk-free) profit. This article walks through a production-grade hedging bot that exploits overreaction dislocations in real time.

Core Mathematical Anchor

In every 15-minute round:

  • One contract settles at $1.00
  • The other at $0.00

Therefore:
Theoretical Fair Sum = 1.00

When market panic pushes one leg sharply lower while the other lags in adjustment, the combined ask price can drop to 0.92–0.97. Buying both legs at that moment locks in guaranteed profit regardless of the final outcome.

Opportunity Trigger: Dump + Dislocation

The bot monitors only the first few minutes of each round (high volatility window).

Detection Logic:

  • One side drops > MOVE_PCT (e.g. 12–18%)
  • Immediate price imbalance between Up and Down

Original Serial Approach vs Improved Concurrent Lock

Original (Serial): Buy Leg 1 on dump → passively wait for Leg 2 to become cheap.

Improved (Concurrent Dual-Leg): At the moment of dump, simultaneously:

  1. Place limit buy on the dumped leg (Leg 1) at dump_ask + slippage
  2. Reverse-calculate Leg 2 price = SUM_TARGET - leg1_price
  3. Submit both orders in parallel using concurrent execution 
function executeBothLegs(symbols, dumpSide, dumpAsk) {
    const leg1Symbol = dumpSide === "Up" ? symbols.up : symbols.down;
    const leg2Symbol = dumpSide === "Up" ? symbols.down : symbols.up;

    const leg1Price = _N(dumpAsk + SLIPPAGE, 4);
    const leg2Price = _N(SUM_TARGET - leg1Price, 4);

    const goLeg1 = exchange.Go("CreateOrder", leg1Symbol, "buy", leg1Price, SHARES);
    const goLeg2 = exchange.Go("CreateOrder", leg2Symbol, "buy", leg2Price, SHARES);

    // Wait and confirm both
    state = STATE.BOTH_PENDING;
}
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This proactively locks the arbitrage spread instead of hoping the market comes back.

Risk Management Layers (Critical for Live)

  • Single-leg exposure protection: If only Leg 1 fills and Leg 2 never does → apply FLOOR_PRICE stop + EARLY_TAKE_PROFIT
  • Last-minute logic: In final LAST_MIN_S seconds, cancel pending Leg 2 and either hold or stop-loss Leg 1
  • On-chain latency handling: Order timeout, retry, and confirmation loops (Polymarket CLOB + blockchain delays)
  • Auto Redeem: After settlement, automatically call redeem to recycle capital 
function handleLeg1OnlyRisk(...) {
    if (holdBid <= FLOOR_PRICE || holdBid >= profitLine || (isLastMin && holdBid <= stopLine)) {
        cancelAndConfirmUntilClear(leg2OrderId);
        closePosition(...);
    }
}
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Live Execution Example

New round starts → Down crashes 18.6% from 0.43 to 0.35.

Bot places:

  • Leg 1 (Down) @ 0.37 → filled @ 0.34
  • Leg 2 (Up) @ 0.60

Total cost: 0.94 → Guaranteed $1.00 payout = +6.4% locked profit.

Honest Limitations & Future Improvements

  • Works best in volatile (not calm) markets
  • Single-leg risk requires careful stop parameters
  • Static params → future versions should use dynamic volatility adjustment + external price feeds + option pricing models

This dual-leg hedging framework turns temporary emotional overreactions into deterministic edge. It’s production-ready, battle-tested on Polymarket’s 15-minute crypto binaries, and serves as an excellent base for more advanced Polymarket trading bots (stat arb, market making, cross-market combos).

The beauty lies in its simplicity: no directional prediction needed — just pure structural exploitation of binary market mechanics.

Original Medium Article: Polymarket Binary Hedging Arbitrage: From Concept to Live Execution

If you have more questions, please feel free to contact me at any time: https://t.me/FatherSon97

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