The order book and matching

On HyperCore the order book is protocol state. Every validator applies the same matching rule to the same order sequence, so all reach the same fills (why that matters).

One book per asset

Every perp, spot pair and outcome side has its own book, matched in price-time priority: best price, then earliest arrival. Prices are whole multiples of the tick size, sizes of the lot size (precision).

Perp books hold no margin; the clearinghouse checks it at placement and again for the resting side at match.

Makers move before takers

Say you rest a sell at 3,001 and the price jumps. You cancel; in the same batch, a taker sends an IOC buy at 3,001. Your cancel runs first; the taker finds nothing.

Consensus knows which transactions touch a book and runs each batch in three groups:

Makers get to reprice or withdraw before takers arrive in the same batch.

Per the docs, cancels and post-only orders sent at time t almost always execute before GTC and IOC orders sent at t, across several blocks. Makers escape stale-quote pick-offs, so they can quote tight in volatility.

What this means for you. Post-only (ALO) is the only guaranteed way to be the maker. As a taker, expect quotes to vanish in fast markets.

An order’s life

1. Placement. Via an API server, sequenced, then checked for tick, lot, minimum value and margin. Failure is a rejection; the book is untouched.
2. Matching. Takes crossed liquidity, best price first, and settles each match at once: both accounts update, fees are charged, the maker’s rebate is paid to its wallet.
3. Remainder. GTC rests, IOC cancels the rest, ALO (post-only) is rejected if it would match; triggers (take profit, stop loss) wait for their price, then act as market or limit (order types).
4. End. Filled, or cancelled by the owner or by the protocol with a stated reason.

Outcome markets: one book for two tokens

A HIP-4 outcome’s Yes and No books are one book: buying Yes at 0.62 is selling No at 0.38 (1 minus p). At the same merged price level, resting sells sort before resting buys on the other token (price-side-time priority). Measured on mainnet, an outcome’s two l2Book responses were exact 1 minus p mirrors (market shapes).

The numbers

Parameter	Value
Priority	price, then time (price, side, time on outcome books)
Consensus batches per block	usually 1 to 2
Minimum order value	$10, per the docs’ own error example “Order must have minimum value of $10.”
Open order limit per user	1000, plus 1 per 5M USDC of volume, up to 5000
Outcome price grid	0.00001 to 0.99999 in 0.00001 steps; size in whole contracts
historicalOrders and userFills	at most 2000 most recent entries

The main orderStatus values; the docs list 29, the rest covering open interest caps, liquidation, delisting, vault withdrawals, TP/SL siblings and narrower rejections:

Status	Meaning
open	resting on the book
filled	fully filled
canceled	cancelled by the user
triggered	trigger order fired
rejected	rejected at placement
marginCanceled	cancelled at match time for insufficient margin
selfTradeCanceled	cancelled by self-trade prevention
reduceOnlyCanceled	reduce-only order that would no longer reduce
scheduledCancel	cancelled by the dead man’s switch
badAloPxRejected	post-only order that would have matched
iocCancelRejected	IOC order that could not match
oracleRejected	price too far from the oracle

Reading responses and fills

Each order in a response is {"resting": {"oid": ...}}, {"filled": {"totalSz", "avgPx", "oid"}} or {"error": "..."}. An error inside "status": "ok" is still a failed order.

{ "type": "orderStatus", "user": "0x...", "oid": 77738308 }

oid may be a 16-byte hex client order id (orders). Each match yields two fill rows (taker, maker) with the same notional and tid. Deduplicate on tid, since hash is shared across one order’s partial fills.

Modify, cancel and other limits

• modify works only on resting limit orders and returns a new oid: reconcile a timed-out modify by client order id. One that would cross returns the plain string “Price would cross book”.
• No fill-or-kill, no good-till-date; IOC keeps partial fills.
• With 1000 or more orders open, a new reduce-only or trigger order is rejected.
• The fast-cancel flag cannot cancel trigger orders; a batch containing one is rejected.
• An outcome order that both matches and rests can show in historical order queries as separate primary and dual orders.
• An unquoted outcome book reports a mid of 0.5.

For each order type, see Order types; for quoting against this sequencing, Market making.