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This page answers the questions requesters most often ask when they integrate combos. For the maker workflow and quote rules, see the Combos/RFQ guide. For how payouts work from a user’s point of view, see the Combos FAQs. Combos and RFQs behave the same through the Institutional API and the Retail API. Validation, sizing, fees, and order handling do not depend on which one you use. Treat a combo symbol as opaque. Existing combos use caoc-... and new combos use crossd-....

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Price and Quantity Scales

Does the Reference Data API return combo instruments? No. POST /v1/refdata/instruments does not return combo symbols. Use GetCombos (GET /v1/combos?symbol=...) for a combo’s legs, state, and tickSize. Which scales do I use to decode combo executions? Read them from the order embedded in each Drop Copy execution. order.price_scale and order.fractional_quantity_scale are set on every combo order:
Do not hard-code combo scales. Combos created at different times carry different price scales, and GetCombos does not return a scale. Decode with the values on the order. To look up a combo’s price scale before it trades, use GET /v1/instruments/{symbol}/settlement, which returns priceScale for any exact symbol, including combos. See Fees on execution reports for a worked example.

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Cash RFQs and Fees

Is the combo taker fee included in a cash RFQ’s amount? Yes. For a cash RFQ on a combo, each quoted side is sized to the largest contract quantity whose cost plus the combo taker fee fits within cashOrderQty:
The cost per contract is the price for a requester buy and 1 − price for a requester sell. The fee is the combo taker fee for that quantity, rounded to the cent the same way the exchange charges it. For a sell, the fee curve is evaluated at 1 − price. For example, a $10.00 cash RFQ quoted to buy at 0.1296 sizes to 70.44 contracts: 70.45 contracts would cost more than $10.00. Use the buyQtyDecimal and sellQtyDecimal reported on the quote instead of recomputing them. The fee actually charged is reported per fill in commission_notional_collected. Taker rebates are paid weekly and do not change the fee charged on the fill.

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RFQ Orders on Drop Copy

Which orders does accepting a quote create? After the maker confirms, the exchange submits two ordinary combo orders at the selected price and quantity: the maker’s order first, then yours. Both appear on Drop Copy like any other order on your account. What clord_id does my order carry? The exchange generates it. RFQ-originated orders have a clord_id beginning with rfq1.; treat the rest as opaque. The value is deterministic for a given quote and side, so retrying AcceptQuote cannot create a second order. The quote_executed event delivered to you carries your order’s client_order_id. The public Quote does not include client order IDs. Is the execution’s order.id the quote’s rfqCreatorOrderId? Yes. rfqCreatorOrderId is the exchange order ID of your order, and creatorOrderId is the maker’s. Can executions arrive before GetQuotes shows QUOTE_STATUS_EXECUTED? Yes. The quote moves to QUOTE_STATUS_EXECUTED and records both order IDs after both orders have been submitted. Your order can match immediately on submission, so Drop Copy can deliver its executions before the quote shows the order IDs. Don’t drop executions for an order you can’t yet match to a quote. Hold them and match again once rfqCreatorOrderId is available, or match on the rfq1. prefix and the combo symbol. With restRemainder: false, does my order fill in full in one execution? Not necessarily. With restRemainder: false your order is immediate-or-cancel, not fill-or-kill. It is a normal order on the combo’s order book, so it can:
  • fill in full against the maker’s order
  • fill across several executions, against the maker’s order and other resting orders at the same or a better price
  • fill partially, with the remainder canceled
  • not fill at all
With restRemainder: true, any unfilled quantity rests on the book as a good-til-canceled order. In both cases, Drop Copy is the source of truth for what filled. QUOTE_STATUS_EXECUTED means the orders were submitted; it does not mean they filled.

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Settlement and Positions

How does a combo settle? A combo settles on its own symbol, the same way a regular instrument does, and its settlement price is published on that symbol. Read it with GET /v1/instruments/{symbol}/settlement, which also returns the combo’s priceScale. The legs keep their own settlements. Each leg’s value is:
  • its settlement price for a SIDE_BUY leg
  • 1 − settlement price for a SIDE_SELL leg
The combo settles at the product of those values. A leg that cannot resolve settles at its last fair market price, and the combo’s value is multiplied by that price. See the Combos FAQs for worked examples. Does a combo settle as soon as one leg loses? Yes. Once any leg settles against its side, the combo’s value is fixed at $0, and it settles without waiting for the remaining legs. Otherwise it settles after every leg has a final settlement. Do combo positions appear in account positions? Yes. A combo position is reported under its combo symbol through the Positions API, like any other instrument.

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Leg Combinations

Can I combine legs from the same game? Yes. Legs on the same game or event are allowed, including a spread with the moneyline, as long as the set is possible and not redundant. Which leg sets are rejected? CreateCombo rejects a set of legs that:
  • has fewer than 2 legs or more than the maximum, or repeats a symbol
  • includes a leg that is not open and tradable, or whose market is not eligible for combos
  • cannot all settle as selected, for example buying two outcomes of the same mutually exclusive market, or a winner, spread, and total combination that no final score satisfies
  • contains a redundant leg, one already implied by another leg, for example buying a team’s spread and the same team to win
These rejections return INVALID_ARGUMENT (HTTP 400) with a message describing the first problem found: Separately, RESOURCE_EXHAUSTED with weekly combo creation limit reached means your participant has used its weekly combo creation quota. Is there a way to validate legs before creating a combo? Not currently. Call CreateCombo and handle INVALID_ARGUMENT. Creating a combo that already exists returns the existing symbol and does not count toward the weekly quota.

Combos/RFQ Guide

Maker workflow, quote rules, and last look

RFQ API

RFQ and quote REST and unary gRPC contract

Fee Schedule

Combo taker fee curve and rounding

Drop Copy

Exchange order and fill reconciliation