Fees

How taker and maker fees are charged on XO fills.

XO charges trading fees in collateral (XO USDC), never in outcome tokens. Fees are not part of the signed order — you do not set or sign a fee rate. Settlement applies the market’s taker and maker rates to each filled leg.

Fee rates by market category

Each market category has its own fee rate. Fetch the rate for a token with GET /fee-rate (token_id query param). The response base_fee is the fee rate in basis points used in the curve below.

Rates can differ for taker and maker legs; both use the same conviction curve with their respective rates.

Taker vs maker

Role	Who	What rate applies
Taker	The incoming order that crosses the book	Taker fee rate
Maker	The resting order that provides liquidity	Maker fee rate

Each leg is charged independently from the same fill size and price.

Maker rewards

XO runs a maker rewards program on some markets. On those markets, the maker fee rate is 0 (makers are not charged), and a portion of the fees collected from takers is distributed to makers who provided the resting liquidity. Resting on a rewards-eligible market means you can earn fees when your orders are filled as maker.

Conviction curve

For a filled leg:

fee = C × (feeBps / 10_000) × p × (1 − p)

Symbol	Meaning
C	Filled shares (6-decimal micro-shares on-chain)
feeBps	That leg’s rate in basis points (from GET /fee-rate)
p	Trade price as a fraction in (0, 1) — tick / 1000

p × (1 − p) peaks at p = 0.5 and approaches zero near the extremes, so near-certain outcomes cost almost nothing relative to mid-price fills.

Integer form (floor division):

fee_micro = feeBps × C × tick × (1000 − tick)
            ──────────────────────────────────
            10_000 × 1000 × 1000

How fees are collected

Fees are always collateral (XO USDC), charged to each order’s maker address (the funded trading account on the signed order — not the beneficiary):

• If the leg pays collateral (typical BUY), the fee is added to what that account transfers in.
• If the leg receives collateral (typical SELL), the fee is withheld from proceeds.
• beneficiary (when set) receives net proceeds only; principal refunds and fee funding always stay with maker.

Budget a little extra USDC allowance on the smart account for taker buys so the fee can clear with the principal.

What the API surfaces mean

Surface	Behavior
Signed CTFOrder	No fee field. Do not send or sign feeRateBps.
GET /fee-rate	Returns the market category fee rate for a token_id as { "base_fee": <bps> }.
Trade / WS fee_rate_bps	Compatibility field on fill events — not the source of truth for quoting fees. Use GET /fee-rate.

Fetch base_fee, then apply the curve above to estimate cost for a given size and price.