RESEARCH · VENUE INTELLIGENCE · AUGUST 2026
Two Venues, Opposite Moves
PureStream rebuilds its Liquidity Maker pool around operator classification and admits market makers as a subscriber type. OneChronos goes live in pre-market hours. Both are top-15 ATS venues by FINRA notional. Eight days apart, opposite strategies for growth.
On August 13, PureStream filed a Material Amendment that rebuilds how principal liquidity reaches its institutional subscribers. Under the prior ATS-N, any subscriber could tag its own flow as maker liquidity and route it into a discrete sub-pool of its own. The new filing replaces that with operator-defined classification: order flow is either Primary (institutional) or Liquidity Maker, market makers and principal trading firms become a named subscriber type, and a single Liquidity Maker Supplemental Pool (LMSP) sits alongside a newly defined Primary Pool with anonymized identifiers and a fixed priority hierarchy.
Eight days earlier, OneChronos filed an Updating Amendment confirming that its Early Trading Session, covering 7:00 to 9:30 a.m. ET, is live and the pre-launch testing period has concluded. A venue that ran combinatorial auctions only during regular hours now runs them in the pre-market.
Both are established venues. OneChronos ranks sixth or seventh among all reporting NMS ATSs by weekly Tier 1 notional; PureStream ranks tenth to fourteenth. Both are expanding. PureStream is going deeper, formalizing a counterparty class inside its matching model. OneChronos is going wider, extending the hours in which its existing model operates. The two filings landed eight days apart.
01PureStream: Pool Re-Architecture
PureStream (MPID: PURE, File No. 013-00182) operates a continuous matching venue built around "Liquidity Seeking" (LS) orders. The headline of the August 13 Material Amendment is a pool called the Liquidity Maker Supplemental Pool, or LMSP. The acronym is not new. What the acronym now means is.
Under the ATS-N in force through July 21, "LMSP" stood for Liquidity Maker Sub-Pool, one of three "Sub-Market Matching Instructions" alongside SDSP (Subscriber-Dedicated Sub-Pool) and PRO (Pre-Routing Optimizer). It was an order modifier, not a venue tier. Any subscriber could request an LM ID from PureStream, tag its own firm or conditional orders as maker liquidity, and route them into a discrete sub-pool tied to that single LM ID. Each LM Sub-Pool ran on maker-taker rebate pricing, negotiated per LM ID in a range of $0.0005 to $0.0025 per share. Liquidity seekers could elect to interact with any LM Sub-Pool through an LS ID. The filing was explicit that there was no integration between any Sub-Pool and the ATS central order book.
The August 13 filing replaces that structure. "LMSP" now stands for Liquidity Maker Supplemental Pool, singular, and the question of who counts as a Liquidity Maker moves from the subscriber to the operator. The amendment introduces "transparent and principle-based criteria for Primary order flow eligibility, centered on institutional order flow and strategies," and a corresponding set of criteria and procedures for classifying flow as LM. The term "Primary Pool" does not appear anywhere in the July 21 ATS-N. It is a new defined term. So is the addition of market makers and principal trading firms as a subscriber type, which the July 21 filing did not enumerate.
… a segmented pool that Primary Subscribers may elect to access for additional contra-side liquidity from classified Liquidity Maker ("LM") order flow.
That clause, from the amendment statement, is the architectural core. Primary Subscribers do not automatically interact with LM flow. They elect to. When they do, the filing specifies intra-order type prioritization of Primary orders over LM orders, restricts LM flow to two order types (Streaming Block and ROC), applies a separate fee and rebate structure to LM flow, and gives each Liquidity Maker an anonymized identifier so that Primary Subscribers can evaluate individual LM interactions and adjust their elections. The former PRO instruction and the former LMSP counterparty instructions are removed.
02Before and After the LMSP
The change is easier to see side by side. The left column is the July 21 ATS-N (an Updating Amendment that restated the full form). The right column is what the August 13 Material Amendment states it introduces.
| Dimension | Through Jul 21 ATS-N | Aug 13 ATS-N/MA |
|---|---|---|
| What "LMSP" means | Liquidity Maker Sub-Pool: an order instruction | Liquidity Maker Supplemental Pool: a segmented pool |
| Who decides what is LM flow | The subscriber, by tagging orders through an LM ID | The operator, via published classification criteria |
| Pool structure | One discrete sub-pool per LM ID; no integration with central book | Single LMSP alongside a newly defined Primary Pool |
| Subscriber types | No market maker or principal trading firm category | Market makers and principal trading firms added |
| Access for institutions | Liquidity seekers opt into any LM Sub-Pool via LS ID | Primary Subscribers elect LMSP access; anonymized LM identifiers |
| Priority | Central-book protocols apply inside the sub-pool; "no prioritization or matching benefit to LM order flow" | Intra-order type priority: Primary over LM |
| LM order types | Firm and conditional orders carrying the LMSP modifier | Streaming Block and ROC |
| Pricing | Maker-taker rebates, $0.0005 to $0.0025 per share, negotiated per LM ID | Separate LM fee and rebate structure (Part III, Item 19) |
| Removed | n/a | PRO instruction; former LMSP counterparty instructions |
Read as a whole, the amendment moves PureStream from a venue where principal liquidity was something a subscriber could bring in through its own side door, to a venue where principal liquidity is a recognized participant class with its own pool, its own order types, its own pricing, and a documented place in the priority stack beneath institutional flow. The opt-in survives. What changes is that the operator, not the subscriber, now draws the line between Primary and Liquidity Maker.
The strategic implication follows. PureStream is building a principal-liquidity supply channel that institutional subscribers can use or ignore, and it is doing so at the level of pool architecture rather than as a per-order flag. Venues that commingle institutional and principal flow in a single book, then offer counterparty-selection tools after the fact, put the segmentation burden on the subscriber. PureStream is moving that burden onto itself.
Filing chain context
This is the third Material Amendment PureStream has filed in 2026, and the fourth filing overall. The April 3 MA increased the minimum order size for LS orders from 100 to 1,000 shares. The June 23 MA renamed the post-close session to "OCP Matching Round," expanded ADW peg offsets to basis-point and dollar-and-cent denominations, and extended Minimum Execution Quantity to all LS orders. A July 21 Updating Amendment restated the full form. Read together, the 2026 filings show a venue tightening its institutional character (higher minimums, more precise pegging) while opening a controlled, operator-classified channel for principal liquidity. Those two moves are complementary: the tighter the Primary Pool, the more credible the promise that the LM channel is supplemental rather than commingled.
03OneChronos: Extended Hours
OneChronos (MPID: CGXS, File No. 013-00156) operates a combinatorial auction venue. Where most dark pools match orders bilaterally, OneChronos runs periodic auctions that solve for optimal allocations across multiple participants simultaneously, using a mechanism it calls "Expressive Bidding." Subscribers specify customizable execution constraints (Bidder Logic) and the venue's matching engine computes the allocation that maximizes aggregate price improvement dollars across eligible orders, subject to those constraints.
The August 5 Updating Amendment confirms the operational fact that matters: the Early Trading Session, covering 7:00 a.m. to 9:30 a.m. ET, has launched and the pre-launch testing period has concluded. Testing ran through June 16; the session went live June 17. All order types and instructions available in the Regular Trading Session are available in the early session. The same filing adds one handling rule: where the ATS marks an order ineligible during its market-quality and risk checks, that order stays ineligible until it becomes executable in a subsequent auction, unless its time-in-force requires cancellation.
The filing chain
OneChronos has filed ten times in 2026, four of them Material Amendments. Read in order, the Updating Amendments are refinements of the MAs rather than changes in their own right.
- May 4 (MA). Early Trading Session announced with a June 10 launch, alongside a new point of presence at Equinix NY3 and a negotiated commission rate of $0 to $0.0015 per share on orders in sub-dollar-priced securities.
- May 29 (MA). ATS personnel with access to confidential trading information provide services to Operator affiliates, and affiliate personnel have such access when providing services to the ATS.
- June 5 (MA). The Operator may disable a Subscriber from interacting with or generating Conditional Invitations; firm orders may opt in to generate them regardless of time-in-force.
- June 9 (UA). Launch moves to June 17; the NY3 point of presence is established.
- June 26 (UA). The May 29 affiliate-access disclosure is expanded (OneChronos UK, OneChronos NL, OneChronos FX).
- June 29 (UA). The June 5 Conditional Invitation rules are refined, and a new 10% NBBO price guard marks overly aggressive external prices ineligible.
- August 5 (UA). The session is live and the pre-launch testing period has concluded.
What makes this worth attention is not the 150-minute extension itself. Pre-market trading exists on every exchange and most large dark pools. What is noteworthy is that OneChronos is running combinatorial auctions in the pre-market. Regular-hours auctions can rely on dense order flow and tight SIP quotes to calibrate their allocations. The pre-market environment is thinner, with wider spreads and less reliable reference prices. Running an optimization engine designed for regular-hours density in pre-market conditions is a bet that the Expressive Bidding framework is robust enough to produce useful allocations even when participation is lighter.
The Equinix NY3 point of presence deserves a note. The current ATS-N describes the matching engine and the original PoP at Equinix NY5 (800 Secaucus Road), with an additional PoP at NY3 (600 Jefferson Avenue). New subscriber cross-connects now land at NY3. Order eligibility for each auction is determined by the timestamp at whichever PoP receives the order, so a second PoP is not just capacity: it widens the set of subscriber locations that get equal-footing timestamps. That the PoP was filed in the same Material Amendment as the Early Trading Session suggests OneChronos expects the extended hours to bring in connections it did not previously have.
04FINRA Volume Context
Both venues report under FINRA Rule 4552. Across the seven weeks from June 8 through July 20, 2026, the tape shows two established, actively traded venues. Ranked by Tier 1 weekly notional against every NMS-equity ATS in our index that reported that week (32 to 34 venues), OneChronos finished sixth or seventh in all seven weeks. PureStream finished between tenth and fourteenth.
All figures below are Tier 1 only, averaged across the seven weeks, so the two venues are compared on the same basis.
PureStream (PURE)
OneChronos (CGXS)
OneChronos runs nearly twice PureStream's weekly notional (1.8 times over the window) on fewer than two-thirds as many trades, so its average execution is about three times larger in dollar terms. Both venues sit inside the top 15 by FINRA notional every week in the window. These are not startups filing structural amendments from a standing start. They are mature venues with established subscriber bases making deliberate architectural changes.
Publication lag note
FINRA publishes Tier 1 data on approximately a two-week lag and Tier 2 on approximately a four-week lag, so the weeks of July 13 and July 20 carry Tier 1 only. Everything in this section is therefore Tier 1 only, including the earlier weeks where Tier 2 is available. Charting the combined figure for five weeks and the Tier 1 figure for the last two would have shown OneChronos declining from $49.1B to $43.6B across the final three weeks, when on a like-for-like Tier 1 basis it rose from $41.9B to $43.6B. Over the five weeks where both tiers are published, Tier 2 added 13 to 20 percent to PureStream's Tier 1 notional and 17 to 24 percent to OneChronos's. Every figure here understates the eventual total.
05The Divergence
Every ATS faces the same growth constraint: more volume requires either more participants, more hours, or more order types. PureStream and OneChronos have each chosen a different dimension to expand, and the choices are revealing.
PureStream is going deeper. The re-architected LMSP turns principal liquidity from a subscriber-tagged side channel into a recognized participant class (market makers and principal trading firms) with an operator-classified, opt-in pool beneath the Primary Pool. The bet is that institutional subscribers will value the additional contra-side liquidity enough to elect access, while the anonymized identifiers and priority hierarchy will prevent the adverse-selection problems that plague venues where institutional and principal flow are commingled. If it works, PureStream gets to serve two ecosystems from one venue without compromising its pitch to either.
OneChronos is going wider. The Early Trading Session extends the combinatorial auction model into pre-market hours without changing who participates or how orders interact. The bet is that enough order flow arrives between 7:00 and 9:30 a.m. to make the optimization engine produce useful allocations in a thinner environment. If it works, OneChronos captures pre-market crossing volume that currently goes to simpler venues, and its existing subscribers get an additional 150 minutes of auction-based execution per day.
It would be neat to say the SEC's own filing categories capture the difference, and it would be wrong. Both were filed as Material Amendments. OneChronos filed the Early Trading Session as an ATS-N/MA on May 4; adding hours was material, not administrative. What differs is where each venue sits in that cycle. OneChronos's structural filings ran from May into early June, and the August 5 Updating Amendment is the close-out: it deletes two dates that had gone stale, the testing cutoff and the launch, and records that the session is running. PureStream's structural filing is the August 13 one. Read in sequence, the two venues are not at opposite ends of a regulatory taxonomy. They are at opposite ends of the same process, one finishing a change and one starting it.
Neither strategy is unprecedented, though the PureStream one is rarer than it looks. Letting subscribers restrict who they trade against is ordinary, and Form ATS-N has an item devoted to counterparty selection that venues across the industry populate. Expressing that choice as pool structure is not ordinary: across every current Form ATS-N in our filing index, PureStream's is the only one that uses sub-pool language at all. Extended hours, by contrast, are common across exchanges and several dark pools. What is unusual is two established, top-15 venues filing eight days apart with strategies that cover different axes of the same growth problem. It is a clear snapshot of where structural competition in U.S. dark pool infrastructure is heading in the second half of 2026.
06Explore the Filings
Everything in this note came out of two public sources: the operators' own Form ATS-N filings on SEC EDGAR and FINRA's Rule 4552 weekly volume data. Sapinover Venue Intelligence indexes both across every NMS-stock ATS, with the full filing text, machine-parsed change summaries, and per-venue volume history. The four links below open the exact records used here.
The Venue Intelligence overview is open to all readers. Venue profiles, the compare tool, and the filing index are part of the Institutional tier.
References
- PureStream, LLC. Form ATS-N/MA, filed August 13, 2026, accession 0001798802-26-000006. Primary Pool classification criteria, Liquidity Maker Supplemental Pool, market maker and principal trading firm subscriber types. SEC EDGAR, CIK 0001798802
- PureStream, LLC. Form ATS-N/UA, filed July 21, 2026, accession 0001798802-26-000005. Full restated ATS-N; source for the prior LMSP (Liquidity Maker Sub-Pool), SDSP, and PRO Sub-Market Matching Instructions and LM ID rebate range in Part III, Items 5, 7, 14, and 19.
- PureStream, LLC. Form ATS-N/MA, filed June 23, 2026, accession 0001798802-26-000004. OCP Matching Round, MEQ for all LS orders, ADW peg offset denominations.
- PureStream, LLC. Form ATS-N/MA, filed April 3, 2026, accession 0001798802-26-000003. Minimum LS order size increased from 100 to 1,000 shares.
- OneChronos Markets LLC. Form ATS-N/UA, filed August 5, 2026, accession 0000902664-26-003321. Early Trading Session live, testing concluded, ineligible-order handling. SEC EDGAR, CIK 0001692652
- OneChronos Markets LLC. Form ATS-N/UA filings of June 9 (0000902664-26-002733, launch moved to June 17, NY3 PoP established), June 26 (0000902664-26-002896, affiliate personnel access), and June 29, 2026 (0000902664-26-002942, Conditional Invitations, 10% NBBO price guard).
- OneChronos Markets LLC. Form ATS-N/MA, filed May 4, 2026, accession 0000902664-26-002252. Early Trading Session introduced (7:00 to 9:30 a.m. ET), Equinix NY3 point of presence, commission fees on Sub-Dollar Orders. Part III, Items 5, 6, and 11 of the current ATS-N describe the NY5 and NY3 PoPs and PoP-timestamp eligibility.
- FINRA Rule 4552 ATS Transparency Data. MPIDs PURE and CGXS, weeks of June 8 through July 20, 2026. Rank computed against all ATSs reporting Tier 1 NMS volume in each week. FINRA OTC Transparency
- Sub-pool uniqueness: case-insensitive text search for sub-pool terminology ("sub-pool" or "subpool") across each venue's most recent complete restated Form ATS-N in Sapinover's filing index, as of August 15, 2026. PureStream's July 21, 2026 filing is the only match, and remains the only match under every venue-deduplication method tested.
- Sapinover Venue Intelligence: PureStream profile, OneChronos profile, and ATS-N filing index.
This analysis is sourced entirely from public SEC EDGAR filings and FINRA Rule 4552 transparency data. It does not constitute investment advice, a recommendation, or a solicitation. ATS-N filings are the operators' own disclosures; Sapinover has not independently verified the completeness of the information disclosed. FINRA volume figures are subject to the publication lag described above. For methodology, see the support page.