Post‑Only, Reduce‑Only, GTC, IOC and FOK in Crypto Futures

You submit a price and quantity that look valid, yet the order disappears. Before removing every advanced setting and trying again, identify what the instruction was designed to prevent. A post-only cancellation can mean it refused an immediate taker fill. An FOK cancellation can mean it refused an incomplete position. Both outcomes may be correct even when there is some liquidity at your price.

These controls answer different questions. Post-only decides whether the order may take existing liquidity. Reduce-only decides whether it may increase or reverse exposure. Time in force decides what happens when the full quantity cannot execute immediately. They are not interchangeable “safer trade” switches, and enabling every available option is not a coherent execution plan.

Start from the intended change in the account. “Sell at this target without ever opening a short” needs an exposure restriction. “Buy only if the entire quantity is available now” needs an all-or-none immediate instruction. “Quote a bid and wait, but never cross the offer” needs maker-only behavior. The words after the price and quantity determine which of those requests you have actually sent.

The examples below use order-book perpetuals and explicitly named product behavior. An instruction can be exposed as a checkbox on one venue, an order subtype on another, or a parameter available only in certain position modes. Matching the displayed name is not enough to establish that every possible combination is supported.

Consider a request for ten contracts at a chosen limit price. Six contracts are immediately available at that price or better. Good till canceled, or GTC, can execute six and keep four working. Immediate or cancel, or IOC, can execute six and cancel four. Fill or kill, or FOK, requires all ten immediately and therefore executes none in this situation.

Change the available quantity in the exercise. At zero availability, GTC can keep the full request open, while IOC and FOK leave no resting order. At ten or more, both IOC and FOK can achieve the full request in this deliberately frozen book. Their difference becomes important when the available amount is smaller than requested.

IOC accepts a smaller result; FOK rejects it

Use IOC when an immediate partial execution is still useful and you do not want an old remainder trading later. For example, a trader reducing exposure may accept a smaller reduction now, then reassess the remaining position. IOC removes the unfilled instruction; it does not remove the exposure that failed to close.

FOK fits a different requirement: the proposed trade is useful only at its full size within the stated price boundary. It can avoid an unwanted partial leg, but it does not make separate trades on different exchanges execute atomically. If one leg fills and a second venue rejects its own FOK, the first trade still exists. “All or none” belongs to the individual accepted instruction.

GTC fits a price-based request that remains relevant after the immediate opportunity passes. That persistence is also its cost. If your view changes, the leftover order can fill hours later while you are thinking about a different trade. The quantity still working deserves a place in the exposure plan rather than being treated as a harmless historical entry.

A GTC request remains actionable after a partial fill. If only its price or quantity is amended, inspect the updated order rather than assuming the exchange created a wholly separate position.

Time in force governs whether an unfilled remainder may stay in the book. IOC cancels the unmatched remainder immediately; GTC leaves it resting, subject to contract validity and risk controls.

Post-only protects maker participation. If a Bybit order would execute against an existing quote immediately, it is canceled rather than accepted as a taker fill. A canceled request may therefore have obeyed your instruction.

Repricing can preserve passive intent, but price may move away while you wait. For an urgent reducing exit, decide whether maker participation is still a requirement rather than removing the constraint automatically.

A one-way account holds a long of 12 SOL contracts, each representing the same fixed contract unit. A trader creates a sell exit for all 12. Before that exit fills, another closing action reduces the long to 5. The old instruction is now larger than the exposure it was intended to remove.

If the sell is unrestricted and all 12 execute, the first 5 close the remaining long and the next 7 create a short, assuming the account permits that reversal. Reduce-only prevents the excess from becoming a new opposite position. The venue can shrink or cancel the instruction according to its rules, but it must not treat an exposure-increasing fill as an eligible reduction.

Quantity protection and execution probability are separate

Reduce-only does not force the remaining 5 contracts to close. A price-limited sell still needs suitable bids, and a post-only sell can still be canceled if it would cross. The instruction restricts which position changes are permitted; it does not solve a lack of counterparties or override another execution condition.

A reduce-only buy also cannot reduce a long. The order direction has to oppose the position it targets. With no relevant position, there is nothing to reduce. Bybit documents rejection of new reduce-only orders in that situation. Turning the restriction off merely to make the order pass can create the very new exposure the setting was meant to prevent.

Several exits can compete for the same remaining position. Imagine three profit targets totaling more contracts than are left after a manual reduction. Do not assume every original target retains its full quantity. Bybit documents resizing or canceling reduce-only orders, including adjustments to more distant prices when nearer eligible exits already cover the available position.

The practical follow-up after a partial manual close is therefore to inspect the remaining targets. An automatically resized order may be appropriate, while a canceled distant target may need no replacement at all. Recreating every canceled exit at its old size can restore an over-allocation rather than repair a problem.

Separate the lifetime or execution choice from the exposure restriction. In Bybit’s order API, GTC, IOC, FOK and PostOnly are alternative values of a single time-in-force field. Reduce-only is a separate parameter. You do not send IOC and PostOnly simultaneously and expect the engine to decide which one wins.

The first four rows express different ways to reduce an existing position. They do not imply that a request larger than the reducible position will be accepted unchanged. A valid combination of fields can still fail a quantity, direction or balance-related check. Compatibility is about whether the instructions make sense together, not whether a particular trade is guaranteed.

Post-only plus reduce-only can be useful, but it is deliberately patient

A resting take-profit sell can combine both objectives: it should never open a short, and it should never take liquidity on arrival. That combination suits an optional maker exit. It conflicts with an instruction whose first priority is to get out immediately. The settings are neither universally good nor universally bad; their fit depends on the exit’s purpose.

FOK plus reduce-only needs extra care when the position is changing. A full-size close prepared a moment earlier may exceed the current reducible amount after another order fills. Refresh the position quantity and inspect the accepted order size. Do not interpret “fill all” as permission to sell more than the remaining position or as a guarantee that the engine preserves the original requested quantity.

An attached profit or stop instruction for a new entry is a different object from a reduce-only closing order. If an interface refuses additional TP/SL fields on a closing request, removing reduce-only is not necessarily the right remedy. The closing order may simply have no reason to create another pair of exits after it has reduced the position.

In hedge mode, the contract, position side and reducing instruction must identify the leg to close. Buy/Sell alone is insufficient because opening a new long and closing a short are both purchases.

Canceling and resubmitting a resting quote is not economically identical to leaving it alone. The new order reaches the book at a new time. Where matching uses price-time priority, that can put it behind other orders at the same price. Repeatedly chasing the top of the book may therefore change both execution probability and the price you are willing to accept.

Kraken’s derivatives documentation gives a concrete amendment distinction: reducing quantity preserves the order’s queue position, while changing its price or increasing its quantity sends it to the back of the price-time queue. Apply that statement to the documented Kraken product; do not assume every other venue uses identical amendment rules.

There is also a race between a fill and a cancellation. If 2 of 10 contracts execute before a cancel takes effect, the completed 2 remain part of the position. Replacing the canceled request with another full 10 would seek 12 contracts in total. The replacement quantity should reflect the amount still intended, after checking the latest fills and position.

A post-only retry can add another surprise: the first request may have been canceled because it crossed, but a later retry at the same price may rest because the quote changed again. That does not make the earlier cancellation erroneous. Each submission faces the book that exists when it arrives, and repeated attempts are separate orders unless the venue explicitly handles them as amendments.

For a manual trader, the useful habit is simple: read the accepted quantity and current status after an amendment, especially when an exit has reduce-only enabled. For an automated trader, an acknowledgment alone is not the final order state. Keep that implementation detail in the execution system rather than assuming a successful network response proves a completed trade.

A canceled post-only order calls for a decision about maker participation. An incomplete IOC calls for a decision about the position remainder. An FOK rejection calls for a decision about required size. A reduce-only rejection calls for a check of position side and reducible quantity. Removing all restrictions treats four different situations as if they were the same problem.

These observations are starting points, not substitutes for the venue’s actual status and reason. A minimum order size, a price increment or a product restriction can also invalidate an otherwise sensible request. The immediate goal is to distinguish a deliberate execution constraint from a malformed order before changing exposure.

The best instruction is the one whose nonexecution outcome you are prepared to handle. An optional entry can reasonably remain absent; an urgent close may need a revised plan if part remains. Write that next action into the trading plan before the order is sent, instead of letting an unfamiliar cancellation message choose it for you.