Sweep orders
A sweep order, often called an "option sweep" when seen in options chatrooms, is an order that is deliberately broken into multiple pieces and fired at several exchanges at almost the same instant, so it grabs up all the contracts or shares available at the best price on each exchange before moving to the next best price. The name comes from the effect: the order "sweeps" through the order book across venues rather than sitting on one exchange waiting to be filled.
This exists because a stock or option isn't listed on just one exchange. The same contract might trade on a dozen different exchanges simultaneously, each showing its own small pool of buyers and sellers at the top of the book (the best bid and best ask). If someone wants to buy a large quantity fast, taking it all from one exchange would use up the visible supply there and leave a highly visible, single large trade. Instead, a routing system splits the order and sends pieces to many exchanges within milliseconds of each other, filling each venue's available size before the price can move away.
On the tape, this shows up as a rapid burst of smaller trades in the same contract, printed just moments apart, rather than one large print. Traders who scan order flow look for these bursts because tallying them up can reveal a much larger position than any single trade suggests. A sweep is generally read as urgency — the buyer or seller wanted the position now, at the current price, rather than waiting and risking a better price later, which is what a patient limit order sitting on the book would do.
The nuance that trips people up: a sweep tells you about urgency and size, not about intent or being "right." A large sweep can be a directional bet, but it can also be a hedge, part of a spread, an adjustment to an existing position, or something a market maker is doing for inventory reasons that has nothing to do with a view on the stock. Where the trade prints relative to the bid and ask (at, above, or below) is commonly used as a rough clue to how aggressive the buyer or seller was, but it is a clue, not a rule, and reading too much certainty into any single sweep is a common beginner mistake.
Day traders watch for sweeps because they can be an early, visible signal that a large, urgency-driven participant is entering a position right now, before that urgency shows up in price — but the same signal is noisy and needs context (size relative to open interest, where it printed, and what else is happening) before it's actionable.
Suppose XYZ is trading near $50 and its 30-day $55 calls are showing a bid of $1.20 and an ask of $1.30 with modest size on any one exchange. A trader wants 2,000 contracts immediately. A sweep order routes, say, 300 contracts to Exchange A at $1.30, 250 to Exchange B at $1.30, 400 to Exchange C at $1.31, and so on across multiple venues within a few milliseconds, until all 2,000 contracts are filled. On the tape this looks like a rapid string of smaller prints in the same contract rather than one 2,000-lot trade, but scanners that track order flow can add them up and flag it as a single sweep of roughly 2,000 contracts near the ask.
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