September 2026: How the Q1 Speed Wars Continue to Reshape Small‑Cap ETF Spreads

The who, what, when, where and why up front: By September 2026, the Q1 "speed wars" that narrowed quoted spreads in many small‑cap ETFs have largely persisted but evolved. Market‑makers and proprietary trading firms continued to invest in low‑latency data and execution infrastructure through mid‑2026, producing sustained reductions in displayed spreads for many small‑cap and single‑sector ETFs (what), compared with late‑2025 levels (when). These changes are most visible on U.S. lit exchanges during regular trading hours (where) and matter because they change execution costs, order‑routing decisions and liquidity risk for retail investors and institutional traders (why).

Why this still matters: context since Q1

The initial Q1 2026 compression in quoted spreads—driven by faster consolidated feeds, denser co‑location and optimized arbitrage across ETF baskets—did not reverse over the summer. Instead, the market moved from an initial phase of spread compression to a more granular second phase in which:

• Displayed spreads compressed but displayed depth thinned. On many small‑cap ETFs, the one‑to‑five‑share top‑of‑book tightened by roughly 20%–40% versus late 2025, while posted depth at the inside price declined. That pattern means retail market orders face lower visible costs but the quantity available at the best bid/offer is often smaller.
• Off‑exchange and internalization patterns matured. Broker‑dealers and internalizers continued to take a meaningful share of retail-sized executions, particularly odd‑lot and sub‑1,000‑share orders, citing better price improvement opportunities off‑exchange in some names.
• Volatility events exposed fragility in slices of the market. During intraday liquidity shocks in May and again in August 2026, several thin small‑cap ETFs saw wider instantaneous effective spreads and larger realized tracking deviations, underscoring vulnerability when high‑speed liquidity providers step back.

New data and examples through August–September 2026

Market‑analytics firms and broker self‑reports filed through August 2026 show a consistent picture: mid‑quote spreads for a broad basket of small‑cap ETFs remain materially narrower than in 2025, while average trade size at the NBBO has declined. For example, in a representative sample of 40 small‑cap ETFs tracked by independent analytics firms, median quoted spread narrowed about 28% year‑over‑year through August 2026, while median displayed depth at the inside price fell about 15%–25% depending on the ETF.

Real‑world episodes illustrate the tradeoffs. On August 11, 2026, intraday selling pressure in several regional small‑cap names coincided with a rapid widening of effective spreads on related ETFs; dealers reported that automated hedging algorithms temporarily paused while firms re‑priced baskets, producing transitory execution slippage for large institutional NAV trades.

Who benefits — and who is exposed

Winners:

• Large, well‑capitalized market‑makers and prop shops that have amortized co‑location and data fees across broader instrument sets. They capture more of the trading flow and the residual rebate revenues.
• Retail traders executing small market orders during U.S. regular hours where posted spreads are tightest—these investors typically see lower visible costs on many tick‑sized ETFs.

Losers or at‑risk groups include:

• Smaller specialist firms that cannot sustain the fixed costs of the latest infrastructure and so lose fill rates and market share.
• Large institutions executing big intraday reallocations who may find headline spreads misleading when trying to trade size; the true depth available off the top of book can be limited during stress.

Regulation and exchange responses — what changed in 2026

Regulators and exchanges stepped up monitoring in 2026. U.S. exchanges implemented incremental feed‑handling improvements and expanded historical tick‑level reporting available to market‑structure researchers. Several broker‑dealers updated their Rule 605/606 disclosure templates in mid‑2026 to provide more ETF‑specific fill and routing statistics through June and July, giving investors clearer visibility into on‑ and off‑exchange execution mixes. Expect continued regulatory attention on whether faster markets are also resilient markets.

Practical guidance for investors — what to do now

For stock investors and DIY ETF traders, the operating rules have shifted slightly. Current best practices through September 2026:

• Choose execution method by order size and time of day. For sub‑500‑share trades during mid‑day, a market order often benefits from narrower displayed spreads. For larger intraday trades or pre‑open/close windows, use limit orders or work with algos that can slice orders to minimize market impact.
• Request ETF‑specific execution reports from your broker. Ask for recent Rule 605/606 summaries and sample fills for the ETFs you trade. Compare on‑exchange NBBO prints with your fills to spot differences in price improvement patterns.
• Plan large reallocations in advance. For institutional or large retail rebalances, contact an execution desk or liquidity provider to access hidden depth, crossing networks or internal block liquidity rather than expecting the top‑of‑book to suffice.
• Monitor volatility windows. Spreads are narrowest mid‑day; pre‑open, the opening cross and close remain times of elevated effective costs for small‑cap ETFs.

Impact and what to watch next

Over the next 3–6 months (through Q1 2027), watch three developments closely: (1) whether exchanges produce additional feed upgrades that restore more displayed depth; (2) any formal regulatory proposals aimed at disclosure or minimum displayed depth for ETF markets; and (3) how the concentrated footprint of market‑makers affects liquidity during the next extended market stress episode. Each will materially affect execution economics for both retail investors and institutions.

FAQ — Common questions investors ask now

Are small‑cap ETF trades cheaper to execute in September 2026 than in 2025?

Generally yes for small retail trades conducted during U.S. regular hours: displayed spreads for many small‑cap ETFs remain materially narrower than in late 2025. However, available size at the inside price is often smaller, so larger trades can still face higher effective costs.

Should I stop using limit orders for small‑cap ETFs?

No. For very small, routine trades during mid‑day, market orders may cost less on average. But use limit orders for pre‑open/close trades, larger sizes, or when you need price certainty—especially in names with thin displayed depth.

Does off‑exchange execution mean worse outcomes for retail investors?

Not necessarily. Off‑exchange internalizers and crossing venues can and do offer price improvement for retail orders. The key is transparency: ask your broker for fill‑level data and compare executed prices to NBBO prints to confirm whether price improvement is real.

How should large investors approach liquidity now?

Large investors should pre‑trade with an execution desk, use liquidity‑seeking algorithms, and consider negotiated fills or block crosses. Don’t rely solely on displayed top‑of‑book when executing multi‑million‑dollar ETF trades.

Bottom line: The Q1 2026 speed upgrades delivered sustained spread benefits by September 2026, but they also produced thinner visible depth and more complex routing dynamics. Savvy investors will use the tighter display to their advantage for small trades while applying more disciplined execution planning for larger allocations.