RESEARCH · ATS REGULATORY INTELLIGENCE · JULY 2026

The ATS Filing Tape

What 1,116 ATS-N filings and two years of FINRA volume reveal about where U.S. dark venues are competing

Sapinover Research · July 13, 2026 · Sources: SEC EDGAR Form ATS-N corpus (1,116 filings, 44 venues, 2019–2026) and FINRA Rule 4552 ATS Transparency Data (36 MPIDs, 119 weeks)

01The Filing Tape

Form ATS-N comes in five flavors: an initial registration, Updating Amendments (UA) for routine changes, Material Amendments (MA) for operationally significant ones, Correcting Amendments (CA), and SEC-ordered amendments (OFA) filed when regulators direct a venue to revise its disclosure. Across the full corpus, the split is 659 UA, 293 MA, 129 CA, 30 OFA, and 5 initial registrations.

Two features stand out. First, 2025 was the busiest year on record at 188 filings, and 2026 is running hotter still: 112 filings in barely six months annualizes to roughly 210. The dark-venue industry is amending its rulebook faster than at any point since Form ATS-N took effect. Second, the composition is shifting — the routine-to-material ratio is stable, but SEC-ordered amendments, historically a rounding error, became a visible band in 2025.

02What's Changing

Tagging each filing by the sections it touches reveals where the competitive energy is going. Three categories dominate, and they describe the same contest from three angles: how the venue matches (execution logic), what instructions it accepts (order types), and who is allowed to trade there (subscriber access).

The 2026 material amendments make the pattern concrete. A representative sample of this year's highest-impact changes:

• Level ATS opened to the buyside — adding Asset Managers and Hedge Funds as a non-broker-dealer subscriber class with a dedicated due-diligence process (subscriber access).
• IBKR EOS added Non-Displayed Orders and defined their priority behind displayed orders on price parity (order types).
• Goldman SIGMA X2 introduced Participant Categories, a new counterparty-segmentation dimension (execution / counterparty selection).
• Moon ATS added midpoint- and primary-peg order types and, separately, moved clearing from Apex to Instinet — two material amendments in a single week (order types + service providers).
• OneChronos expanded its Expressive Bidding service to allow two target orders per expressive order and to let bidder logic incorporate operator-supplied market data (execution logic).
• AlphaX US introduced an Enhanced IOC order type able to interact with firm and conditional orders (order types).

None of these are cosmetic. Each changes what an institutional desk can do at that venue — the raw material of routing decisions.

03The Regulatory-Friction Signal

SEC-ordered amendments (ATS-N/OFA) are the clearest public signal of regulatory engagement with a venue: they are filed when the Commission directs a change rather than the operator volunteering one. From 2019 through 2021 there were none. Then came a trickle — four in 2022, four in 2023, two in 2024 — before a step-change to fifteen in 2025, with five more through mid-2026.

“Ordered amendments went from a rounding error to a fifteen-filing year. The pressure is concentrated in exactly the venues doing something new.”

That pressure is heavily concentrated. Five venues account for all 30 ordered amendments, and two account for 22 of them.

The concentration is not evidence of wrongdoing — it is the signature of novelty. Blue Ocean pioneered the first genuinely overnight U.S. equity ATS, a model with no direct precedent for the Commission to lean on, and its sixteen ordered amendments span a continuous fifteen-month review as that model was refined into effectiveness. Intelligent Cross runs a latency-equalizing match that similarly broke new ground. The lesson for the rest of the field is instructive: the further a venue's design sits from established templates, the longer and more iterative its path through SEC review.

04Volume vs. Filing Intensity

The intuitive assumption is that the biggest venues file the most — more flow, more machinery, more to disclose. The data says the opposite. Filing intensity and trading volume are largely decoupled.

Read the corners. UBS ATS is the second-largest venue by share volume yet filed just eight times since 2024 — a large, stable, mature book. Citi-ONE and Blue Ocean sit at the opposite extreme: modest volume, but among the most-amended venues in the industry. Intelligent Cross is the rare venue that is both the largest by volume and a heavy iterator. The takeaway is that filing cadence measures how actively a venue is reinventing itself, not how much it trades. Young venues and novel models amend constantly to find product-market fit; incumbents with settled mechanics leave their disclosures alone.

05The Tier 2 Drift

FINRA splits ATS volume into Tier 1 (S&P 500 components) and Tier 2 (all other NMS-listed names). Across 2026, Tier 2's share of weekly ATS volume climbed from roughly 46 percent early in the year toward 51 percent — dark liquidity is migrating down the market-cap scale. But the aggregate hides enormous dispersion across venues.

The spread is an archetype map. Blue Ocean at 85 percent Tier 2 reflects its overnight, retail-adjacent flow in smaller names. IBKR at 65 percent and CrossStream at 57 percent sit in the same neighborhood. At the other end, the big broker-dealer block pools — Goldman SIGMA X2, the Morgan Stanley venues, UBS — cluster around 44 to 45 percent, weighted toward large-cap institutional crossing. A venue's Tier 2 mix is effectively a fingerprint of who it serves, and the industry-wide drift upward says the marginal new dark volume is coming from below the S&P 500.

06What We're Watching

The filing tape leads the volume tape. Material amendments to execution logic and subscriber access are, in effect, product launches — and product launches precede the volume they are designed to attract. Three threads are worth tracking through the back half of 2026:

• Buyside access. Level ATS opening to asset managers and hedge funds is the kind of subscriber-access change that can re-rate a venue's addressable flow. Watch whether peers follow and whether it shows up in Level's Tier volume.
• Order-type convergence. Multiple venues added or reworked peg and non-displayed order types this year. As menus converge, execution quality — not feature availability — becomes the differentiator.
• The novelty tax. With SEC-ordered amendments concentrated in the newest models, the pace at which Blue Ocean and Intelligent Cross clear their review cycles is a leading indicator for how the next wave of unconventional venues — overnight, auction-based, or tokenized — will be treated.

For an institutional desk, the practical implication is that the ATS-N docket is an early-warning system. A venue's material amendment today is the routing option, the counterparty rule, or the access change that reshapes its liquidity six months out. Reading the filing tape is how you see it coming.