FAK

FAK (Fill-And-Kill)

A FAK order is a Fill-And-Kill order: it attempts immediate execution against available resting orders and cancels any unfilled remainder. On Polymarket the user-facing “market order” button submits a FAK order with built-in slippage protection so you either get immediate fills up to your price tolerance or the leftover quantity is cancelled.

In context

On Polymarket, trading happens through a CLOB. When you click the market buy or sell button the frontend sends a FAK order to the CLOB, not an unconditional sweep. The Relayer and CLOB enforce slippage limits and the order executes only against currently available best bids/asks. If the book cannot fully satisfy the quantity within your tolerated slippage, the unfilled portion is cancelled rather than being posted as a resting limit order.

Practical implications

• Execution intent: FAK prioritises immediacy. It never posts the remaining quantity to the book.
• Slippage protection: Polymarket’s market path includes automatic checks so you won’t unknowingly accept extreme prices; partial fills up to the tolerance will execute, remainder is cancelled.
• Fees and fills: Taker fees apply to executed quantity; maker fees are zero but do not apply because FAK consumes liquidity. Watch for partial fills and fee differences across categories.
• Risk considerations: A FAK’s apparent immediacy doesn’t eliminate resolution risk, slippage, settlement timing, smart-contract risk, or oracle disputes. Never assume an execution is without risk.

See also

• /glossary/clob
• /glossary/spread