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How matching works
Each instrument has one order book. Sellers rest asks on it with a limit price and a token capacity; buyers arrive with a bid and a ceiling.
Which ask fills
Matching is price-time priority. The engine takes the cheapest ask at or below your ceiling that still has capacity; where two asks are priced the same, the one that rested first goes first.
You are filled at the resting ask price, not at your ceiling. Bidding higher widens the set of asks you are willing to take — it does not raise what you pay. If the best ask is $0.24 and your ceiling is $0.30, you pay $0.24.
A fill larger than one ask's remaining capacity consumes it and continues to the next ask; a fill smaller than the ask leaves the remainder resting.
There is one global book per instrument. region on a bid is a filter —
omit it to sweep every region — not a separate market.
When nothing crosses
Live chat completions are immediate-or-cancel: they fill against what is on the
book right now, and cancel whatever is left over. If no ask sits at or under
your ceiling, nothing fills and you are not charged — the request returns
402 with no_fill_at_limit. Raise the ceiling, retry later, or buy a
capacity ticket instead of waiting on the spot price.
Time in force, for capacity tickets
Tickets can say what should happen to an unfilled remainder.
| Time in force | Behaviour |
|---|---|
gtc | Rest the remainder on the book until it fills or you cancel it. Default. |
ioc | Fill what is available now, cancel the rest. |
fok | Fill the whole quantity now, or reject the order outright. |
Take and market orders are always immediate-or-cancel; asking for gtc on one
of those is treated as ioc.
When an ask leaves the book
An ask rests until one of these happens:
- it fills completely,
- the seller cancels it,
- its
ttl_secondselapses — five minutes if the seller did not set one, - or the seller is suspended. A seller who breaches the latency SLA repeatedly has their live asks pulled from the book and cannot rest new ones until the cooldown ends. See SLA enforcement.
A resting order is durable: it survives a restart of the exchange, so a gtc
remainder does not quietly disappear.
Related: the spot market for what is traded, and settlement for what happens after a fill.