Requote

A response that belongs to one execution model. Where an order is treated as a request to deal at a named price, the firm checks whether that price is still available when the request arrives. If the market has moved beyond the tolerance the order allowed, the firm declines it and returns a new price. Nothing has been executed at that point: the position is unchanged, the new price is an offer, and the market can move again while it is being considered.

The cause is latency of a very ordinary kind. A quote is displayed, a request travels to the server, and the market moves in between, which is why requotes cluster where prices move fastest: around scheduled releases, at the open of a thin session, and in a gapping market. The alternative model treats an order as an instruction to deal at whatever is available, so the same market movement is expressed as a fill away from the requested price, which is slippage rather than a requote.

The two are constantly confused and they are not the same event. A requote is a refusal followed by a fresh offer, so the price is certain and the execution is not. Slippage is an execution at a different price, so the execution is certain and the price is not. Neither model removes the movement that caused it, which is the point most often missed: a platform that never requotes has not eliminated the cost, it has relocated it into the fill. Practitioners disagree about which model is preferable, and the disagreement turns on which of the two certainties matters more to a given method rather than on one model being better priced.