Options Flow Alerts — Sweeps, Blocks, Splits & Aggressor Logic

Options flow alerts flag notable options trades in near real time — the kind of activity that may signal informed positioning. Unusual Whales' Flow Alerts and Full Tape classify each trade by how it executed (sweep, block, split), where it printed (at the ask vs at the bid), and therefore who was the aggressor and whether the trade reads bullish or bearish. Understanding these tags is what separates reading flow from chasing noise.

Sweeps vs blocks vs splits

These describe the execution mechanics. A sweep, per UW, is "an order that executed as multiple trades across multiple exchanges" — a (typically larger) order that "sweeps different exchanges (hence intermarket sweep) with the goal of filling their order at the best prices currently offered." Sweeps signal urgency: the trader prioritized getting filled now over getting the best single price. A block is "a large order privately negotiated and executed away from the public exchange auction, typically due to size" — one big, pre-arranged trade printed at once. A split is "similar to a sweep, but only on a single exchange" — a large order executed as multiple smaller trades on one venue. Sweeps imply speed/urgency; blocks imply a large player taking size deliberately; splits sit in between.

At-ask vs at-bid — where the trade printed

The price location relative to the bid-ask spread reveals which side was aggressive. A trade printed at the ask means a buyer paid up to lift the offer — the buyer was the aggressor consuming liquidity. A trade printed at the bid means a seller hit the bid — the seller was the aggressor. UW: a trade of calls "executed on the ask price would hold a bullish thesis because we can predict that the trader is purchasing those calls," while puts bought on the ask "hold a bearish thesis." Trades that fill at the midpoint leave the aggressor undetermined. This is why every flow alert carries a side tag — it is the difference between someone aggressively opening exposure and someone passively providing it.

The aggressor concept

The aggressor is "the one opening the trade, either with a market order or marketable limit order." UW's rule: "if buying is done at the ask or above it, then liquidity is being consumed at fair market value, and this is done by an aggressor. Conversely, if selling is done at the bid or lower, then that is also done by aggressors." A fill "merely at the midpoint between the bid and the ask" leaves the aggressor undetermined. Identifying the aggressor matters because it tells you who wanted the trade badly enough to cross the spread — that side is generally the one expressing conviction.

Bullish vs bearish premium

Combining instrument (call/put) with side (ask/bid) yields the directional read. UW: "If a call trades on the ask/offer, or a put trades on the bid, a bullish sentiment would be attached to the trade as all things constant, these trades increase in value on a move higher in the stock." And: "If a call trades on the bid or a put trades on the ask/offer, a bearish sentiment flag would be attached... these trades increase in value on a move lower." So the four combinations are: call-at-ask = bullish, put-at-bid = bullish, call-at-bid = bearish, put-at-ask = bearish. Aggregating the dollar premium on each side (premium = the dollar cost of the trade) gives net bullish vs bearish premium for a ticker.

Unusual volume

Flow becomes "unusual" when activity is large relative to context — typically option volume that is high versus the contract's own average and, critically, versus its open interest. Comparing today's volume to existing open interest hints at whether a trade is opening new exposure (volume large relative to prior OI, OI likely to rise) or closing old positions. UW's alert rules layer additional filters — minimum premium thresholds, sweep counts, and combinations (for example the "Sweeps Followed by Floor" alert fires when "a series of sweep orders (minimum 10) are soon followed by a large floor trader (minimum premium of 100000)"). The point of the filters is to surface size and urgency that stand out from ordinary two-sided market-making.

How to read flow without being fooled

Side and execution tags tell you who was aggressive, not why. An aggressive call sweep at the ask is the textbook bullish print, but it can equally be a dealer hedge, a roll of an existing position, a closing buy-to-cover, or one leg of a spread whose other leg you cannot see. The disciplined read combines several confirmations: the side (ask/bid), the trade type (sweep urgency vs block size), the premium (dollar conviction), and the next-day open-interest change (did the position actually open?). Treat a single alert as a data point, not a signal; weight clusters of aligned aggressive flow far more than any one eye-catching ticket.

Common mistakes

The classic error is "big call sweep = someone bullish, follow it." Calls bought at the ask are bullish all else equal, but all else is rarely equal — the trade may be a hedge, a closing trade, or a spread leg. A second mistake is reading premium size as edge: a multi-million-dollar trade says conviction in dollars, nothing about whether the thesis is right. A third is ignoring open interest — without checking whether volume opened or closed positions, you cannot tell new exposure from an exit. Use UW's tags to characterize the flow precisely, then corroborate with OI change, the underlying tape, and the broader positioning picture (GEX, NOPE) before acting.