Cboe’s price-improvement auctions (including AIM, SAM, and complex auctions like COA) are short-timer mechanisms where multiple parties race to provide (or take) liquidity at a better price than the displayed market.
That race has an unglamorous constraint: message queues. If the exchange is busy enough, a response that was submitted in time can still miss the auction because it sat behind other inbound traffic waiting to be processed.
The SEC approved a Cboe rule change (SR-CBOE-2025-074) that is designed to reduce that specific failure mode.
This article is market-structure context and options education only. It is not financial advice, investment advice, trading advice, or a recommendation to buy or sell anything. Options trading involves risk and is not suitable for all investors. See the site’s Risk Disclosure.
What changed (high level)
Per SEC Release No. 34-105080 (SR-CBOE-2025-074), Cboe amended the rules around auction-response processing:
- For standardized, non-FLEX options classes, the maximum combined window (auction response/exposure period plus the additional time allowed to process already-received messages sitting in the inbound queue) can be up to 1,000 milliseconds.
- The “up to 1,000ms” ceiling that previously existed in limited form for non-FLEX SPX is effectively made permanent as part of the broader framework.
- FLEX options are excluded from this queue-processing continuation logic.
If you trade via a retail broker, you are not “sending auction responses” yourself in the typical sense - but this still matters because your order can be routed into auction mechanisms, and the competitive response set affects your fill price.
What did NOT change (important misconception)
This rule change does not give participants extra time to decide and submit auction responses after the timer ends.
The cut-off is still the cut-off. The concept is:
- an auction runs for its defined response period,
- when the auction period ends, the exchange may continue processing its inbound queue only for messages that were already received before the end time (based on the exchange’s timestamping),
- the auction executes after the exchange processes those timely-received messages or hits the maximum allowed processing window.
That distinction matters because some commentary about “a longer auction” incorrectly implies a slower or more gameable auction. The intent here is the opposite: to preserve fairness for timely participants when traffic spikes.
Why This Matters For Options Traders
Even if you never think about auctions, this kind of rule change can show up in the places traders actually feel:
- how often you see real competition in an auction, especially in fast markets,
- how repeatable your fills feel when your broker routes into price-improvement mechanisms,
- how much “weirdness” you see during volatility spikes (wide markets, mass cancels, rapid re-quoting).
The practical effect is likely to be most noticeable in:
- high-traffic moments (macro events, sharp market moves, market makers updating quotes constantly),
- auction-heavy flow (AIM/SAM routing is a meaningful share of certain retail-sized marketable flow),
- index options and other classes where message traffic can be extreme.
The “trader-level” translation:
- Fewer “ghost” auction outcomes where it looks like little competition showed up, when in reality competitive responses were submitted but didn’t get processed fast enough.
- A higher chance that the “best” response among timely submissions is actually considered, which can support better auction outcomes on average.
Hypothetical example (not advice): you submit an order that gets routed into an auction during a fast tape. Liquidity providers respond, but the exchange is processing a deep inbound queue (orders, quotes, mass cancels). Under the old ceiling, a response that arrived in time could still miss the execution if it wasn’t processed by the cut-off. The rule change aims to make “arrived in time” mean “gets a fair shot at being processed,” within a bounded maximum window.
None of this is a guarantee of price improvement. It’s plumbing that can reduce one reason an auction underperforms.
What traders may misunderstand (and how to think about it)
1) “This gives everyone an extra second to respond”
No. Responses still must arrive before the auction ends. The added time is for processing already-arrived messages stuck in a queue.
2) “This means the market is slower / more delayed”
The rule sets an upper bound. In many cases the extra time actually used can be much smaller; it is not “a guaranteed 1-second delay” added to every auction.
3) “Price improvement stats are the same as best execution”
Price improvement is measured versus NBBO and other reference points. It can be a useful metric, but it is not the whole best-execution story. For many self-directed traders, disciplined limit-order usage is still foundational. If you want a refresher: Common options trading mistakes (and how to avoid them).
Practical checklist (what to do with this information)
- Treat this as execution-quality context, not a directional signal.
- Prefer limit orders and be explicit about acceptable price.
- If you rely on “marketable” orders, understand how your broker routes them and when they’re eligible for auctions.
- When spreads are wide or conditions are fast, expect the auction/microstructure layer to matter more than usual.
Sources
- SEC: Release No. 34-105080 (SR-CBOE-2025-074) - Notice of filing + order granting accelerated approval; outlines the 1,000ms framework and FLEX exclusion.
https://www.sec.gov/files/rules/sro/cboe/2026/34-105080.pdf - Cboe rule filing PDF: SR-CBOE-2025-074 - filing text/background and rule-language context.
https://cdn.cboe.com/resources/regulation/rule_filings/pending/2025/SR-CBOE-2025-074.pdf - Cboe technical overview: Titanium U.S. Options Auction Process - background on AIM/SAM-style auction mechanics and message handling.
https://www.cboe.com/document/tech-spec/document/technical-specifications/cboe-titanium-u.s.-options-auction-process
