Fill or Kill – An order instruction requiring that the entire order be filled immediately or not at all. FOK orders are “all-or-nothing”; if the full quantity cannot be executed instantly at the specified price, the order is canceled entirely. This ensures no partial positions. In practice, FOK is used by robots when a trade must enter or exit completely (for example, to scale in/out quickly). A robot might set TimeInForce.FillOrKill (if supported by its API) to implement this behavior. FOK avoids unwanted partial positions but risks no execution if liquidity is insufficient.

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