FINRA's weekly ATS transparency data ranks venues by shares. That ranking is consistent and auditable — and it produces a competitive picture disconnected from the notional value transferred. We pulled ten weeks of issue-level data for the top 14 venues by shares, matched it against a 9-venue FINRA notional dataset, and mapped which names drive the tape — and where.
The result challenges a simple narrative. It's not that different ATSs route fundamentally different stocks. SPY, NVDA, MSFT, AMZN — every venue routes them all. The difference is how much of each name concentrates at each venue. UBSA (UBS ATS) routes $11.7 billion in SPY T1 notional over ten weeks. IATS (IBKR ATS) routes $1.1 billion in the same name over the same period. That 10x gap in one name, across the same tier, is the structural story.
Below the mega-cap layer, the structural signal becomes a tier signal. Twelve of fourteen venues run 50–62% T1 by share count — a band tight enough to define an industry norm. Two venues sit outside it: BLUE (BOATS (Blue Ocean ATS)) at 13.2% T1 and IATS at 37.5%. Those outliers are analyzed separately. The tier-split analysis covers 14 venues on a share basis; the notional analysis covers the 9 venues with reported FINRA notional data.
Venue Reference
All venues are identified by MPID (Market Participant Identifier — the FINRA ATS identifier, distinct from ISO MIC codes) throughout this analysis. The full registered name and operator for each of the 14 venues is listed below.
00The Dataset: Full Universe by Tier
The analysis draws from FINRA's ATS Weekly Transparency Data, published weekly via the FINRA public API (api.finra.org/data/group/otcMarket/name/weeklySummary). Each row is a symbol-level weekly summary: one record per MPID per symbol per week, reporting Total_Shares and Total_Notional transacted in that seven-day window. The window below covers 10 complete trading weeks, Feb 02 through Apr 06, 2026.
How notional is calculated: FINRA receives trade reports from each ATS and publishes the weekly aggregate notional directly as the Total_Notional field. This is not estimated — it is the sum of (price × shares) for all transactions reported by that MPID in that week for that symbol. No VWAP estimation or price approximation is applied. The figures are reported in US dollars.
| Tickers | Observations | Total Shares | Total Notional | % of Grand Total | |
|---|---|---|---|---|---|
| NMS Tier 1 | 2,447 | 126,571 | 17.53B shares | $1,685.6B | 73.4% |
| NMS Tier 2 | 9,781 | 493,447 | 23.71B shares | $610.6B | 26.6% |
| TOTAL | 12,224 | 620,018 | 41.24B shares | $2,296.2B | 100% |
NMS Tier 1 covers securities in the S&P 500, Russell 1000, or with a national market system designation meeting FINRA's liquidity threshold. Tier 2 captures everything else — including large foreign listings (ADRs), leveraged ETFs, and small-cap domestics. The tier is determined by the security's benchmark classification, not its price or ATS volume.
The 9,781 T2 symbols represent a long tail: the top 100 T2 names by notional account for the majority of T2 notional, while the remainder distribute across micro-cap and low-liquidity names. Tier 2 is not a monolithic category — it contains ultra-premium ADRs like ASML ($1,391/share) alongside sub-$1 micro-caps routed through venues like XSTM (ONDS at $9.96/share) and IATS (CRWV at $86/share).
01The Mega-Cap Names Driving T1 Notional
Across 9 ATSs and 12,224 unique symbols in the Feb 02–Apr 06, 2026 window, $1.69 trillion in Tier 1 notional was reported to FINRA. The top 10 symbols by notional — SPY, NVDA, MU, MSFT, AMZN, TSLA, QQQ, AVGO, META, GOOGL — account for $247 billion, or 14.7% of all T1 flow. The top 25 names reach 23.2%.
The concentration is shallower than expected. Twelve thousand symbols compete for T1 share, and the top 10 hold only 14.7% of notional. The remaining 86% distributes across a long tail of liquid but lower-notional securities. SPY at $48 billion represents 2.8% of total T1 notional on its own — more than any other single name, but far from dominating.
Semiconductors appear three times in the top 10 (NVDA, AVGO, and GOOGL's AI infrastructure adjacency). ETFs anchor positions 1 and 7 via SPY and QQQ. The implied average price per share across these names ranges from $182 (NVDA) to $668 (SPY) — all high-dollar assets generating outsized notional per share.
02Where Each Name Trades: The Name × Venue Routing Map
The table below maps the top 8 T1 names against the 9 venues with FINRA notional data. Darker cells indicate higher notional concentration. Each cell shows $B over ten weeks. Row totals reflect the 9-venue sum; the full 14-venue universe would be larger.
Several patterns emerge from the matrix. PURE (PureStream) and MSTX (MS Trajectory Cross) concentrate in equity names — NVDA, MSFT, AMZN, AAPL each show $3–7B at PURE and $2–4B at MSTX. UBSA (UBS ATS) dominates SPY at $11.7B, roughly double any other venue. IATS (IBKR ATS) leads in TSLA at $4.9B — nearly double BIDS at $1.2B — consistent with IBKR's retail-adjacent client base concentrating in high-volatility names.
SGMT (Sigma X2) leads in SPY at $6.7B among the institutional venues. Goldman's Sigma X2 showing high SPY concentration is consistent with block-trading and program-execution flows where S&P 500 hedges move through the ATS.BIDS (BIDS ATS) concentrates in NVDA ($5.7B) and SPY ($5.1B), consistent with a buyside-focused block matching profile.
02bVenue Deep Dive: All 16 MPIDs, Top 5 T1 & T2 by Notional
The cards below profile all 16 MPIDs in the dataset, sorted by total notional (T1 + T2 combined). Each card shows the venue's T1 and T2 notional bars (scaled to MSTX as the maximum), symbol counts, share volume, and the top 5 names by notional in each tier. Avg price per share is computed as Total_Notional / Total_Shares from FINRA-reported data — not estimated.
03The Structural T1/T2 Split
The share-based tier split analysis covers 14 venues from FINRA issue-level data. Twelve of fourteen venues run 50–62% T1 by share count — a band defining the structural industry norm. Two sit outside it: BLUE (BOATS (Blue Ocean ATS)) at 13.2% T1 and IATS (IBKR ATS) at 37.5%.
The 9-percentage-point spread between INCR (IntelligentCross) at 52.5% and PURE (PureStream) at 61.3% encompasses venues operating very different client books. The convergence is not a regulatory artifact — no rule requires a 55% T1 ratio. It reflects the underlying composition of NMS-eligible trading: the liquid securities in Tier 1 attract more flow at roughly this ratio.
BLUE's 13.2% T1 concentration is the most extreme case. Of its 5.06 billion total shares, only 668 million are T1. IATS at 37.5% is structurally T2-heavy but within a standard deviation of the peer group in a way BLUE is not. When both are mapped to the name-level routing matrix, they tell different stories: IATS concentrates in expensive T1 names (including leading TSLA at $4.9B); BLUE's T2 book contains a micro-cap sub-population at near-zero per-share prices.
04T2 Surprises: Ultra-Premium Foreign Names
Tier 2 is not uniformly a low-price universe. FINRA's NMS tier classification places non-Russell 1000 securities — including large foreign-listed ADRs — in Tier 2 by market capitalization benchmark. The result is a T2 cohort containing some of the highest-price securities in the dataset.
| Symbol | Name | T2 Notional | Avg Price / Share | Note |
|---|---|---|---|---|
| TSM | Taiwan Semiconductor (ADR) | $18.9B | $353/sh | ADR / non-US primary listing |
| SHOP | Shopify | $10.1B | $119/sh | ADR / non-US primary listing |
| ASML | ASML Holding (ADR) | $8.9B | $1,391/sh | Ultra-high price, small share count |
| CRWV | CoreWeave | $8.4B | $87/sh | CoreWeave, recent IPO |
| BABA | Alibaba (ADR) | $6.8B | $142/sh | ADR / non-US primary listing |
| SOXL | Direxion 3x Semis Bull ETF | $5.2B | $59/sh | 3x leveraged ETF — classified T2 |
| ARM | Arm Holdings (ADR) | $5.2B | $133/sh | ADR / non-US primary listing |
| MELI | MercadoLibre | $5.0B | $1,829/sh | Ultra-high price, small share count |
Taiwan Semiconductor (TSM) at $18.9 billion T2 notional over ten weeks is the most striking case. It places TSM roughly equal to QQQ ($18.9 billion) in T1 notional — one of the most actively traded ETFs in the world — but entirely in Tier 2. At $353/share implied average, TSM generates significant notional per trade.
ASML at $1,391/share and MercadoLibre (MELI) at $1,829/share are the highest per-share T2 names in the dataset. Both are classified T2 because they are non-US primary listings (ADRs), placing them outside the Russell 1000 threshold. Their T2 notional is small in share count but meaningful in dollar terms.
SOXL — the Direxion 3x Semiconductor Bull ETF — appearing at $5.2 billion T2 notional reflects a specific classification mechanic: leveraged and inverse ETFs are frequently excluded from Tier 1 benchmarks regardless of their notional size.
05T2 Price Spectrum: $3.19 to $13.91 Across Venues
Looking at the venue-level T2 average price (from the share-based 14-venue analysis), the per-share T2 composition spans from $3.19 at MSPL (MS POOL) to $13.91 at IATS (IBKR ATS) — a 4.4x spread across a single tier.
IATS (IBKR ATS) at $13.91/share T2 is the outlier. Its Tier 2 book contains securities — including TSLA, NVDA, and SPY-class names — that FINRA classifies as T2 in this window. At $13.91 average, IATS T2 carries more per-share notional than the T1 book of several peer venues.
MSPL (MS POOL), MSTX (MS Trajectory Cross), and CGXS (OneChronos) cluster at the bottom. Their T2 books concentrate in lower-priced large-cap names — stocks trading in the $2–$15 range — generating large share counts at limited notional.
BLUE (BOATS (Blue Ocean ATS)) at $7.24/share T2 sits mid-table. Its anomaly is not the T2 price average — it is the volume of T2: 6.6 times more T2 shares than T1. The T2 average is pulled up by a leveraged ETF cluster (SOXL, SOXS, TQQQ) and pulled down by a micro-cap cluster trading at sub-$0.50.
06BLUE (BOATS (Blue Ocean ATS)) in Context
Placed in the 14-venue table, BLUE ranks #12 by estimated notional — consistent with its #10 share rank. The notional penalty from T2 dominance is partially offset by the leveraged ETF sub-population, which carries real prices. The micro-cap sub-population contributes negligibly to notional despite accounting for roughly 60% of T2 shares.
BLUE's 6.6:1 T2/T1 ratio is not simply a quirk of having a large T2 base. Every other venue in the table runs near parity on shares per tier — the median T2/T1 ratio is approximately 0.9x. No other venue approaches BLUE's ratio.
The economic consequences compound through the share-based fee structure. PFOF paid at $0.002/share generates 0.05 basis points of notional on MU at $401 and 455 basis points on LBGJ at $0.044. ATS fees at $0.003/share represent 6.8% of the traded notional in a $0.044 security. These are the per-trade economics of the micro-cap sub-population at BLUE — running through market structure designed for a $10–$100 stock universe.
Among the 14 venues, BLUE is the only one where the T2 share count is driven primarily by a micro-cap engine. The other high-T2 venues — IATS at 62.5% T2, KCGM at 51.3% T2 — achieve their T2 weight via moderately priced names, not sub-$0.50 flow.
07The Share-to-Notional Rank Inversion
Applying estimated notional to the 14-venue share data (using daily VWAP from ticker prices for top-15 symbols per tier per venue) reorders the competitive table. The largest divergences reveal which venues gain or lose competitive standing when the metric shifts from activity count to economic weight.
| MPID | Full Name | Share Rank | Not. Rank | Shift | Note |
|---|---|---|---|---|---|
| IATS | IBKR ATS | #14 | #7 | +7 | rises sharply |
| KCGM | Virtu MatchIt | #12 | #6 | +6 | rises sharply |
| JPMX | JPM-X | #13 | #8 | +5 | rises |
| UBSA | UBS ATS | #2 | #1 | +1 | drops |
| SGMT | Sigma X2 | #4 | #3 | +1 | drops |
| MLIX | Instinct X | #5 | #5 | — | unchanged |
| PURE | PureStream | #11 | #11 | — | unchanged |
| INCR | IntelligentCross | #1 | #2 | -1 | drops |
| EBXL | LeveL ATS | #3 | #4 | -1 | drops |
| MSPL | MS POOL | #7 | #9 | -2 | drops |
| BIDS | BIDS ATS | #8 | #10 | -2 | drops |
| BLUE | BOATS (Blue Ocean ATS) | #10 | #12 | -2 | drops |
| CGXS | OneChronos | #9 | #13 | -4 | drops |
| MSTX | MS Trajectory Cross | #6 | #14 | -8 | drops sharply |
KCGM (Virtu MatchIt) rises from #12 to #6 (+6 positions). Despite ranking twelfth by shares, Virtu MatchIt's T1 average price of $102/share and T2 average of $11.74/share are both elevated relative to peers. Routing expensive names across both tiers produces notional that share count does not show.
IATS (IBKR ATS) rises from #14 to #7 (+7 positions). IATS holds 37.5% T1 — the second-largest T2 concentration in the universe — but its T2 book is not cheap. A T2 average of $13.91, the highest in the universe, combined with a T1 average of $111/share reflects a book routing expensive names across both tiers. This is consistent with what the name-level matrix shows: IATS leads TSLA T1 at $4.9B.
MSTX (MS Trajectory Cross) drops from #6 to #14 (-8 positions) in the estimated notional ranking. The issue-level FINRA data for MSTX shows Ford (F), AT&T (T), NU Holdings, and SoFi Technologies as top-15 names by share count — these are high-volume cheap names. The share-based estimated notional method captures this by applying their lower per-share prices. The actual FINRA-reported notional for MSTX shows a broader book; the share-count-based estimate reflects the composition of their highest-volume names.
07Takeaway
Three observations from the combined analysis:
1. The mega-cap names are universal; concentration is the variable.Every ATS routes SPY, NVDA, MSFT, and AMZN. The distinction is how much. UBSA routes $11.7B in SPY. IATS routes $1.1B. BIDS routes $5.7B in NVDA. SGMT routes $1.8B in the same name. The competitive signal is not name selection — it is notional allocation per name, which FINRA's share-based ranking cannot surface.
2. T2 contains premium names that the tier label obscures. TSM at $18.9 billion T2 notional, ASML at $1,391/share, and MELI at $1,829/share are classified T2 because their primary listing is non-US. The economic weight of these names rivals T1 mega-caps in dollar terms, but FINRA's tier classification groups them with genuinely low-priced T2 securities. Any competitive analysis treating T2 as a monolithic low-price pool misreads the data.
3. BLUE's structural position remains unique in this universe.No other venue runs a 6.6:1 T2/T1 share ratio. No other venue combines a leveraged ETF sub-population at $20–$57 with a micro-cap sub-population at $0.04–$0.35 within the same T2 book. The PFOF and fee distortion concentrated at BLUE does not generalize to the rest of the 14-venue table.