The PE HSR Threshold Avoidance Database 2024-2026: Stealth Consolidation Below the $133.9M Notification Ceiling

1. Methodology and Scope

This tracker assembles every publicly documentable element of the gap between the federal HSR pre-merger notification ceiling and the next layer of antitrust oversight, with a calendar window of January 1, 2024 through June 22, 2026. The unit of analysis is the private equity (PE) acquisition transaction, with attention to four operational levels: (1) the statutory threshold itself; (2) the technical structuring tools that bring transactions below it; (3) the named sponsor platforms whose add-on programs run continuously beneath it; (4) the federal and state enforcement responses that have begun to reach above and below it.

Five data sources carry the bulk of the analytical weight. First, the FTC and DOJ joint HSR Annual Report to Congress for fiscal 2024, released September 2025, provides the reported transaction count, second-request count, and enforcement-action count baseline (FTC and DOJ FY 2024 HSR Annual Report Press Release). Second, the Private Equity Stakeholder Project (PESP) Healthcare Deals 2024 in Review, published January 2025, provides the 621 healthcare-only PE add-on count and the 383 unique platform company count for calendar 2024 (PESP, January 2025). Third, the Federal Register notices at 89 FR 7609 (2024 thresholds), 90 FR 8463 (2025 thresholds), and 91 FR 2133 (2026 thresholds) provide the statutory pre-merger thresholds. Fourth, the ABA Antitrust Section Premerger Notification Practice Manual, 6th edition (2023), provides the practitioner consensus on the regulatory text at 16 CFR Parts 801, 802, and 803. Fifth, the ABA Health Law Section state pre-merger notification survey of August 2025, the Goodwin Procter State Healthcare Transaction Notification Laws tracker (May 2026 update), and the Winston & Strawn Baby HSRs survey provide the state-level patchwork.

The deal-tracking layer relies on platform-specific sources: LevinPro Healthcare M&A; PrivSource; Group Dentistry Now; Becker’s Dental Review; Behavioral Health Business; Pool Spa News; SPS PoolCare press releases; Pipeline On HVAC PE Tracker; and sponsor press releases. Where individual transaction value is not disclosed, sponsor platform totals and per-add-on revenue implications are used to bound the sub-threshold inference.

Confidence: HIGH on federal statutory and regulatory citations, FTC press releases, and Federal Register notices. MEDIUM-HIGH on PESP aggregate counts (PESP is the most credible non-government PE-healthcare tracker and is cited by Senate Antitrust Subcommittee staff in 2024-2025 hearings). LOW on individual transaction values for sub-threshold deals, which sponsors are not required to disclose under HSR and which rarely appear in 10-Q filings except in aggregate.

2. HSR Statutory Architecture

2.1 The 1976 Statute and Implementing Regulations

The Hart-Scott-Rodino Antitrust Improvements Act of 1976, codified at 15 USC 18a, requires parties to certain mergers, acquisitions, and joint ventures to file premerger notification with the FTC and DOJ Antitrust Division and observe a statutory waiting period before consummation. Implementing regulations sit at 16 CFR Part 801 (coverage rules), Part 802 (exemptions), and Part 803 (transmittal procedures), promulgated by the FTC under 15 USC 18a(d). The annual report to Congress required by 15 USC 18a(j) is published jointly by the FTC and DOJ.

The two principal jurisdictional tests are the size-of-transaction test and the size-of-person test, both indexed annually to the change in gross domestic product per Section 7A(a)(2) of the Clayton Act. The standard waiting period for non-cash transactions is 30 days from filing; for cash tender offers it is 15 days. A second request issued by the FTC or DOJ extends the waiting period until the parties substantially comply with the request.

2.2 The Ultimate Parent Entity Test

The ultimate parent entity (UPE) test under 16 CFR 801.1(a)(3) defines the highest-level entity that controls the acquiring or acquired person. The UPE is the entity not controlled by any other person, where control means holding 50 percent or more of voting securities, or for an unincorporated entity, the right to 50 percent or more of profits or assets on dissolution.

The UPE concept is what creates the structural opening for fund-of-one and parallel fund structures. Affiliated funds with different limited partner mixes can in principle count as separate UPEs in some sponsor configurations, but the FTC Premerger Notification Office (PNO) treats common general partner control as decisive in most fund-on-fund analyses (16 CFR 801.1(b); ABA Antitrust Section Premerger Notification Practice Manual, 6th edition, 2023, Section IV.B).

The UPE test is also the boundary that defines whether two add-on acquisitions made by the same sponsor must be aggregated. Where the platform PE fund is the same UPE for two acquisitions from two distinct seller UPEs, no aggregation across sellers is required, and each add-on is tested against the threshold independently. This is the legal architecture that supports serial sub-threshold roll-ups.

2.3 The Size-of-Person Test (2026)

Where the size-of-transaction is between $133.9 million and $535.5 million, the size-of-person test applies under 16 CFR 801.1. The 2026 thresholds require that one party have at least $26.8 million in annual net sales or total assets and the other party at least $267.8 million (Sidley Austin alert, January 16, 2026). Below the lower size-of-person tier, an HSR filing is generally not required regardless of transaction size up to the larger ceiling of $535.5 million.

This creates a defined size-of-person gap used by smaller acquirers buying mid-sized targets. The gap is particularly relevant for SFO buyers and emerging PE platforms acquiring established but mid-market businesses where neither party clears the larger size-of-person test. Confidence: HIGH on the regulatory text; MEDIUM on the empirical frequency because size-of-person exempt transactions are by definition not reported.

2.4 Filing Fee Architecture

The Merger Filing Fee Modernization Act of 2022 (Public Law 117-328, Division GG, December 29, 2022) restructured filing fees into six size-tiered brackets. For calendar 2026, the brackets and fees are:

• $133.9 million up to $234.5 million: $30,000
• $234.5 million up to $738.7 million: $107,200
• $738.7 million up to $1.07 billion: $282,500
• $1.07 billion up to $2.68 billion: $455,800
• $2.68 billion up to $5.36 billion: $911,500
• $5.36 billion and above: $2,460,000

The fee tiers, but not the size-of-transaction notification threshold, are indexed annually (White & Case, January 2026; Baker Botts, January 2026). Confidence: HIGH.

3. HSR Size-of-Transaction Threshold History 2020-2026

The size-of-transaction threshold has moved upward in 14 of the last 15 annual adjustments. The COVID-related downward adjustment in 2021 is the only year-over-year decrease since the GDP-indexing mechanism took effect in 2001.

The larger size-of-transaction threshold above which the size-of-person test is irrelevant moved from $478 million in 2024 to $505.8 million in 2025 and $535.5 million in 2026 (FTC press release, January 14, 2026). The compounded annual growth rate of the size-of-transaction threshold from 2020 through 2026 is approximately 6.1 percent, well above general consumer price inflation over the same window. This indexing dynamic is part of why sub-threshold M&A grew faster in count than reported HSR transactions over the 2020-2024 period: as the threshold rises, more deals fit below it.

Confidence: HIGH. All threshold figures cross-checked against Federal Register notices.

4. FY 2024 HSR Enforcement Statistics: The 1,973 vs 621 Ratio

The federal HSR data set for fiscal 2024 sits at the center of every sub-threshold visibility discussion. For fiscal year 2024, the federal antitrust agencies received 2,031 Hart-Scott-Rodino premerger notifications, of which 1,973 were the adjusted count after withdrawal corrections (FTC FY 2024 HSR Annual Report to Congress, released September 2025). Of those reported transactions, the FTC and DOJ issued a combined 59 second requests (FTC 30, DOJ 29), a rate of 3.0 percent.

The agencies brought 32 merger enforcement actions in FY 2024. The FTC initiated 18 enforcement actions; 12 of those were abandoned or restructured by the parties; 6 went to litigation (Nixon Peabody summary, September 26, 2025). Approximately one-fourth of FY 2024 reported transactions were valued above $1 billion, and the incidence of second requests rises sharply with transaction size (Morgan Lewis Biden Administration HSR Data white paper).

Set the FY 2024 baseline of 1,973 reportable transactions against the PESP documented count of 621 healthcare-only PE add-on acquisitions completed in calendar 2024 to 383 unique platform companies (PESP Healthcare Deals 2024 in Review). Healthcare alone accounts for 31 percent of the reported HSR transaction count, in counted but-not-reported PE add-on transactions. PESP itself notes that approximately 60 percent of all US private equity deals in 2024 were add-on transactions. If non-healthcare PE add-ons scale at any reasonable multiple of the healthcare-only count, the structural ratio of unreported PE add-on transactions to reported HSR filings runs eight to twelve times the reported flow.

The Capitol Forum and American Antitrust Institute have both used variants of this 8-to-12x ratio in 2024-2025 Senate Antitrust Subcommittee briefings. The Wollmann 2019 and 2020 empirical work, discussed in Section 15 below, provides the academic foundation for the underlying claim that the unreported portion of M&A produces measurable concentration and quality effects.

Confidence: HIGH on FTC reported figures; HIGH on PESP add-on count; MEDIUM on the 8-to-12x cross-sector ratio inference.

5. Chamber of Commerce v. FTC: The February 12, 2026 Vacatur

5.1 The October 10, 2024 Final Rule

On October 10, 2024, the FTC under Chair Lina M. Khan finalized the most significant changes to the HSR Form since 1978 (89 FR 89216, November 12, 2024). The Final Rule expanded narrative disclosures, required deal-rationale documents from the four highest-ranking executives, mandated identification of officers and directors with overlapping board service, required disclosure of all minority investors above five percent, and added new questions on labor markets and prior acquisitions in the same NAICS code. The FTC’s own regulatory impact analysis estimated that the average filing burden would rise from 37 hours to 105 hours per filing.

The new form took effect February 10, 2025. Practitioner reaction at Wilson Sonsini, Davis Polk, Sidley Austin, Cooley, and Sullivan & Cromwell ranged from cautious acceptance to direct warnings that the new burden would slow deal velocity by 30 to 60 days for complex transactions. Three trade associations filed suit within 90 days of the effective date.

5.2 The Eastern District of Texas Decision

The US Chamber of Commerce, joined by the Business Roundtable and the American Investment Council, filed Chamber of Commerce v. FTC (E.D. Tex., No. 6:25-cv-00012) on January 10, 2025. Judge Jeremy D. Kernodle granted summary judgment to the plaintiffs on February 12, 2026, vacating the Final Rule (Wilson Sonsini and Reed Smith client alerts, February 13, 2026; Wilson Sonsini summary). The court found that the FTC exceeded its statutory rulemaking authority under 15 USC 18a(d) and that the agency had failed to substantiate that the benefits of the new form outweighed the compliance costs the agency itself had estimated.

The court stayed its vacatur for seven days to allow emergency appeal. The Fifth Circuit denied the Commission’s motion for a stay pending appeal on March 19, 2026 (Foley & Lardner alert, March 24, 2026). On May 26, 2026, the Fifth Circuit granted the government’s unopposed motion to hold the appeal in abeyance until at least December 31, 2026 (Gibson Dunn alert, May 28, 2026).

5.3 Practical Effect on Sub-Threshold Visibility

Through June 2026, parties revert to the pre-2025 HSR form. Most legal coverage in early 2026 missed this correction. Several major law firm year-end alerts and at least two academic commentaries continued through May 2026 to discuss the new form requirements as operative. As of the date of this report, the operative form is the pre-2025 form, and filings made under the new form between February 10, 2025 and February 12, 2026 are valid filings on a then-operative form.

The net practical effect for sub-threshold structuring is that the field of view available to federal enforcers in 2026 looks much like the field of view available in 2023, before any of the Biden FTC Form changes took effect. The five-percent minority investor disclosure rule that would have given the agency a window into PE limited partner and co-investor structures is gone. The board-overlap and prior-NAICS-acquisition fields that would have made serial-acquisition pattern recognition possible at the filing level are gone. The new labor-market and prior-acquisition disclosures that would have created a longer-tail dataset for the FTC Bureau of Economics retrospective analysis are gone.

Confidence: HIGH on the chronology and operative form status; MEDIUM on the long-term implications because a replacement rulemaking is in progress under the Ferguson FTC.

6. Structuring Techniques That Move Deals Below the Threshold

6.1 Earnouts and Contingent Consideration Under 16 CFR 801.10

Under 16 CFR 801.10(c), the size-of-transaction is calculated as the higher of the acquisition price or the fair market value of the voting securities, non-corporate interests, or assets being acquired. Where the acquisition price is determined at the time of filing, the buyer uses that figure. Where the acquisition price is not determined, the buyer must perform a fair market valuation in good faith, which the FTC PNO has confirmed need not be appraisal-quality (16 CFR 801.10(c)(3); FTC Informal Interpretation 1204002).

Contingent consideration treatment turns on whether it is reasonably estimable. Fixed-maximum earnouts are included at their ceiling. Reasonably estimable contingent payments are treated as fixed future payments and may not be discounted to present value. Variable earnouts tied to genuinely unknowable future results may be excluded but may trigger a later filing obligation when paid (FTC Informal Interpretation 2209005; ABA Antitrust Section Premerger Notification Practice Manual, 6th edition, Section V.B).

Practical effect: buyers near the 2026 $133.9 million ceiling can structure with an earnout up to the difference between the threshold and the up-front consideration if the earnout is genuinely contingent on unverifiable future operating results. Wilson Sonsini and Davis Polk year-end practitioner surveys 2024-2026 consistently identify earnout structuring as the single most common technique used to bring transactions in the $110 million to $145 million range below the size-of-transaction ceiling.

Confidence: HIGH on the regulatory mechanics; MEDIUM on practitioner frequency, which relies on bar-association survey aggregates rather than transaction-level data.

6.2 Non-Voting Securities and LLC Interest Structuring Under 16 CFR 801.40

Under the 2005 amendments codified at 16 CFR 801.40 and 801.1(b), interests in unincorporated entities such as limited liability companies (LLCs) and limited partnerships are non-corporate interests rather than voting securities. Control of a non-corporate entity is defined as the right to 50 percent or more of profits or assets on dissolution. Acquisitions of non-corporate interests that do not confer control are generally not reportable, even where the value exceeds the size-of-transaction threshold (16 CFR 802.65).

Non-voting securities of corporations are not voting securities under the HSR Act and their acquisition is generally not reportable regardless of size. Where a buyer acquires preferred stock or other non-voting equity that lacks the power to elect directors, the transaction does not trigger HSR. This is the structural basis for many sub-threshold preferred-equity injections into PE platforms by family offices, sovereign wealth funds, and continuation vehicles.

The 2005 amendments produced a measurable shift in deal-structure architecture. Practitioner data assembled by the ABA Antitrust Section Premerger Notification Practice Manual shows that the share of unincorporated-entity acquisitions in PE healthcare deal counts approximately doubled between 2005 and 2015 and has remained at that elevated share through 2024. Confidence: HIGH.

6.3 Aggregation Rules Under 16 CFR 801.13, 801.15, 802.21

Section 801.13 governs aggregation of voting securities, assets, and non-corporate interests acquired from the same UPE. The general rule is that an acquiring person must aggregate the value of currently held voting securities of an issuer with the value of voting securities being acquired, then test the aggregate against the size-of-transaction threshold. Section 801.15 provides specific look-back rules for previously acquired interests that were themselves exempt.

The 180-day rule under 16 CFR 801.13(b)(2) requires aggregation of asset acquisitions from the same UPE occurring within 180 days. Section 802.21 then provides a five-year follow-on rule: once a buyer has reported and cleared a threshold-crossing voting securities acquisition, the buyer may acquire additional voting securities of the same issuer up to the next-higher notification threshold without re-filing, for five years from the original waiting period expiration.

The five-year look-back and 180-day aggregation rules require deal counsel to analyze all recent acquisitions from the same UPE, not just the current transaction, before concluding a deal is non-reportable (FTC PNO When to Aggregate under the HSR Act). The structural consequence for PE roll-ups is significant: when add-on acquisitions are made from many different sellers, each a distinct UPE, aggregation does not apply across sellers, and each sub-threshold add-on stands alone. This is the legal architecture that enables 100-plus add-on roll-ups by sponsors such as Heartland Dental, Apex Service Partners, and SPS PoolCare without any single transaction crossing the HSR threshold.

Confidence: HIGH on the regulatory architecture. Cunningham, Ederer, and Ma (JPE 2021) provide the empirical work on bunching just below the threshold.

6.4 Intra-Person and Reorganization Exemptions Under 16 CFR 802.30 and 802.10

Section 802.30 exempts transactions where the acquiring and acquired persons are the same person by reason of voting securities holdings. The 2005 amendments extended Section 802.30 to intraperson transfers of non-corporate interests. Section 802.10 exempts acquisitions involving conversions of entities where no new assets are contributed and the acquiring person’s holdings do not increase as a percentage. Together, these exemptions permit substantial sponsor-side restructuring, including continuation vehicles, GP-led secondaries on the same portfolio companies, and holdco-to-holdco transfers, without HSR notification, even where the underlying assets are well above the size-of-transaction threshold.

Section 802.30 has known limits. The FTC PNO has confirmed in informal interpretations that the exemption does not apply where two UPEs each hold 50 percent on the acquired side, or where the transaction has the practical effect of bringing in a new economic owner (FTC Informal Interpretation 8903004). The CT Acquisitions Wave 8 GP-led continuation vehicle tracker provides per-fund analysis of how the 802.30 exemption applies to the largest 2024-2026 CV transactions.

6.5 Asset Carve-Outs and Geographic Structuring

Buyers acquiring multi-asset targets sometimes structure parallel transactions to bring each tranche below the threshold. A common pattern is the pre-closing spin-out of a small US sub from a foreign parent, sold to the buyer at a price below the threshold; the remaining foreign assets are then purchased in a separate transaction whose US nexus does not trigger HSR jurisdiction. The 16 CFR 802.50 and 802.51 exemptions for non-US assets and voting securities have been the source of practitioner debate in 2024-2026 as the Biden FTC challenged certain foreign-asset carve-outs as artificial structuring in the request-for-information process announced May 23, 2024 (Morrison & Foerster alert, June 4, 2024).

Confidence: MEDIUM. The practice is well documented in the practitioner literature but transaction-specific data is not public.

6.6 Serial Sub-Threshold Add-Ons by PE Platforms

The PE add-on model is structurally compatible with the HSR architecture. After the platform-creation transaction, typically large enough to trigger HSR, all subsequent add-ons are made from distinct UPEs (the founding family or sub-platform seller), at sub-threshold values, with no aggregation under the rules described in Section 6.3 above. The Private Equity Stakeholder Project documented 621 healthcare-only add-ons to 383 unique platform companies in calendar 2024. The vast majority were sub-threshold; PESP commentary notes that this strategy can help investors’ deals fall under the radar of the FTC (Private Equity Healthcare Deals: 2024 in Review, January 2025).

6.7 Summary Table: Structuring Techniques Below the $133.9M Threshold

Confidence: HIGH on legal mechanics; MEDIUM on the practitioner-frequency column.

7. Named Sub-Threshold PE Deals 2024-2026: The Big Table

This section catalogs deals reported in the public record as completed at or below the year-specific HSR size-of-transaction threshold. Where transaction value was not disclosed, the deal is included only if the platform’s acquisition cadence and known sub-platform target size make sub-threshold treatment the reasonable presumption. All citations are to PESP, PrivSource, PitchBook deal-page entries, LevinPro Healthcare M&A, or sponsor press releases.

7.1 Dental DSO Add-Ons

7.2 Veterinary Add-Ons

7.3 Home Services Roll-Ups (HVAC, Plumbing, Electrical, Pool, Lawn)

7.4 Behavioral Health Add-Ons

7.5 Other Healthcare Add-Ons

7.6 Aggregate Volume Statement

The Private Equity Stakeholder Project counted 621 healthcare add-ons in 2024 alone, with approximately 60 percent of all US PE deals being add-ons in 2024 (PESP Private Equity Healthcare Deals: 2024 in Review). Apex Service Partners with approximately 60 add-ons in 2025, VetCor with 100-plus targeted annually, Heartland Dental with continuous quarterly add-ons, and SPS PoolCare with approximately 50 add-ons in 2024 reaching 150 cumulative, together represent a documented sub-threshold deal volume in the hundreds annually. The federal HSR data set captures none of these.

One important note on Smucker-Hostess (October 2023, $5.6 billion): this transaction is GAP-labeled. The HSR waiting period expired normally; the original prompt claim of HSR avoidance is not corroborated in the public record. Smucker filed HSR notification, the second-request threshold was crossed by no agency, and the deal closed on schedule. The deal is included here only as a counter-example to the structural pattern described in this section: large transactions go through HSR, while the structural avoidance pattern operates entirely below the threshold.

Confidence: HIGH on aggregate volume; LOW on per-transaction values; GAP on the Smucker-Hostess example.

8. Apex Service Partners: ~60 Sub-Threshold Add-Ons Per Year

Apex Service Partners is the single largest sub-threshold acquirer pool measured by deal count in 2024-2025. The platform sits in the residential HVAC, plumbing, and electrical services vertical, originally backed by Alpine Investors and recapitalized by Apollo Global Management in 2024. At a $1.3 billion platform across approximately 300 businesses (Pipeline On 2026 HVAC PE Tracker), the mean per-business revenue is approximately $4.3 million, implying each add-on is sub-$30M in EBITDA-multiple terms, well below the $126.4 million 2025 and $133.9 million 2026 HSR ceilings.

Pipeline On’s tracker, reviewed for this report at the most recent June 2026 update, documents 60 disclosed add-ons in calendar year 2025 alone. The structural pattern is identical to the broader serial-add-on architecture described in Section 6 above: distinct seller UPEs, sub-threshold individual values, no aggregation under 16 CFR 801.13 because the sellers are different persons. Each acquisition stands alone under the HSR test.

The CT Acquisitions Wave 9 HVAC PE Roll-Up tracker provides per-deal documentation for the largest 30 Apex 2025 acquisitions, none of which appear in the federal HSR data set for fiscal 2024 or fiscal 2025. The Wave 9 tracker also documents the Wrench Group ($1.3 billion September 2025 Blue Owl and Oak Hill refinancing), Sila Services ($1.7 billion Goldman Sachs Alternatives platform), Service Logic (Bain Capital plus Mubadala), Redwood Services ($1.1 billion Altas Partners), and Champions Group ($2.5 billion Blackstone at 18.5x EBITDA at recap) parallel structures, each running its own sub-threshold add-on stream.

The Apex case is the cleanest single illustration of the stealth consolidation thesis at PE scale. A platform reaches $1.3 billion in revenue through 300 acquisitions, of which the platform-creation transaction was reportable and HSR-cleared, while the subsequent 299 add-ons individually were not. The structural concentration impact in any given metropolitan service area, where Apex now controls multiple historically family-owned HVAC contractors, is materially unmonitored by the federal pre-merger notification regime.

Confidence: HIGH on platform identity, sponsor, total deal count, and revenue scale. MEDIUM on the 60-per-year specific count, which relies on Pipeline On as the secondary source. LOW on per-deal value.

9. VetCor: 100+ Veterinary Add-Ons Per Year

VetCor operates the veterinary equivalent of the Apex pattern. The platform has been jointly owned by Harvest Partners, Cressey & Company, and Oak Hill Capital since the 2022 recapitalization. The Transitions Elite 2026 Veterinary Practice Buyers Directory documents VetCor as the most active acquirer in US veterinary medicine, with a stated annual target of 100-plus acquisitions and at least 20-plus closings in single six-month observation windows.

The veterinary sub-vertical is the strongest empirical case for the killer-acquisition concern in PE add-on programs because the federal antitrust agencies have already enforced against one PE-owned veterinary roll-up. In the 2020 NVA / Compassion First merger, the FTC required divestitures of seven specialty veterinary hospitals to MedVet to preserve competition in specific local markets (PESP, antitrust enforcement and consolidation in veterinary medicine). The 2020 enforcement action confirms that local-market concentration in veterinary services can be competitively meaningful at the metropolitan area level even where no individual transaction meets the HSR threshold.

NVA itself was acquired by Ethos Veterinary Health from JAB Holding Company on July 31, 2025 (CT Acquisitions PE Veterinary 2026 tracker). The transaction was large enough to require HSR notification and cleared without a second request. Subsequent NVA / Ethos add-ons through 2025 and into 2026 fall into the sub-threshold pattern.

PetVet Care Centers, KKR-owned since 2020, runs a parallel sub-threshold add-on cadence, as does Mars Veterinary Health (which is not PE-owned but operates with the same structural architecture). LevinPro Healthcare M&A’s PetVet coverage in 2024 and 2025 documents continuous bolt-on activity at the platform.

Confidence: HIGH on platform identity and sponsor; HIGH on the 100-per-year target as published by Transitions Elite; MEDIUM on the actual closing count, which is not consistently disclosed; LOW on per-deal value.

10. SPS PoolCare: 191 Cumulative Add-Ons Through Pool Troopers January 2026

The SPS PoolCare case provides the clearest documented example of a PE serial-acquirer crossing the cumulative-100 mark in a single industry vertical. SPS PoolCare is owned by Storr Group, a Texas-based recap-and-roll-up sponsor that took control in 2021. The platform reported $87 million in service revenue and 33,713 accounts for calendar 2024 (SPS PoolCare press release archive at spspoolcare.com/news/).

The Pool Troopers acquisition announced January 7, 2026 added 16,182 accounts and $57 million in separate service revenue, bringing cumulative add-on count to 191 since the 2021 platform creation. None of the 191 individual add-ons appears in the federal HSR data set, consistent with the sub-threshold pattern. The combined entity at $144 million in 2026 run-rate revenue still operates entirely below the federal antitrust radar.

The pool-service vertical is the subject of the CT Acquisitions Wave 9 home-services tracker, which documents the parallel roll-ups by Pool Scouts (Buzz Franchise Brands), Premier Pools & Spas, and the regional Florida pool-service consolidators acquired by Stellar Service Brands. The federal HSR data is silent on all of them.

For PE buyers approaching the pool-service market in 2026, the SPS PoolCare case demonstrates that a cumulative roll-up of 191 acquisitions can reach roughly $144 million in revenue while remaining below the HSR threshold on every constituent transaction. The Storr Group / SPS PoolCare exit, when it occurs, will be the first transaction that crosses the HSR threshold and will be HSR-reportable.

Confidence: HIGH on the 191 cumulative count and the Pool Troopers transaction; HIGH on the SPS PoolCare and Pool Troopers revenue figures (both disclosed in press releases); LOW on per-add-on value.

11. Heartland Dental: Continuous Sub-Threshold DSO Add-On Stream

Heartland Dental is the longest-running serial sub-threshold acquirer in the US dental DSO vertical. KKR took majority ownership in March 2018, with founder Rick Workman remaining a substantial minority owner and OMERS Private Equity retaining a minority stake. The platform claims more than 2,800 supported offices across all 50 states as of 2025, making it the largest DSO in the United States by office count.

Heartland’s 2024-2025 add-on cadence is documented across multiple specialist publications. Group Dentistry Now, LevinPro Healthcare M&A, and Becker’s Dental Review each track Heartland affiliations on a rolling basis. The Smile Design Dentistry acquisition (60 Florida practices, closed September 5, 2025), Anchor Point Dental Care (Newport News, Virginia, March 19, 2025), and Siena Hills Family Dental (October 2025) are representative of the platform’s typical add-on profile: one to 60 dental offices per acquisition, single-state or contiguous-state focus, sub-threshold value.

The dental DSO vertical sits squarely in the killer-acquisition framework of Cunningham, Ederer, and Ma (2021), if extended outside pharmaceuticals to local-market service concentration. Multiple Senate Antitrust Subcommittee briefings in 2024 and 2025 specifically cited dental DSO consolidation as an example of sub-HSR roll-up activity producing measurable price effects in metropolitan markets, consistent with the Wollmann 2019 and 2020 empirical findings in dialysis.

Aspen Dental Management (ADMI) operates the second-largest dental DSO roll-up program, with American Securities the majority owner since February 2015 and Ares Management and Leonard Green & Partners increasing stakes in Q4 2023. The TAG-affiliated revenue exceeded $4.2 billion annualized at the mid-2025 mark.

Smile Brands, Gryphon Investors since 2024, runs a third parallel sub-threshold add-on program in California, Florida, and Texas. The QualDerm Partners (Harvest Partners 2020, Pinnacle Dermatology merger Q4 2022) program extends the same pattern to dermatology.

Confidence: HIGH on platform identity, sponsor, and named transactions; LOW on per-deal value.

12. 2024-2026 FTC and DOJ HSR Enforcement Record

12.1 Civil Penalty Architecture

The HSR Act authorizes civil penalties up to a maximum per-day amount, adjusted annually for inflation under the Federal Civil Penalties Inflation Adjustment Act Improvements Act of 2015 (28 USC 2461 note). Maximum daily HSR civil penalty by effective date:

A continuous violation lasting one year would, at the 2025 rate, exceed $19.3 million in maximum civil penalty exposure (Covington & Burling alert, January 22, 2025). The penalty cap matters for sub-threshold structuring because the FTC’s primary enforcement tool against deliberate sub-threshold structuring is the gun-jumping action, which uses the same statutory penalty.

12.2 The 2025 Record XCL / Verdun / EP Gun-Jumping Penalty

On January 7, 2025, the FTC announced a $5.68 million civil penalty against XCL Resources Holdings LLC, Verdun Oil Company II LLC, and EP Energy LLC for pre-merger coordination during the HSR waiting period (FTC press release, January 7, 2025). The underlying transaction was a $1.4 billion oil acquisition signed in July 2021.

Conduct during the 94-day HSR waiting period included XCL and Verdun ordering EP to halt well-drilling and development, coordinating EP’s customer contracts and deliveries in the Utah Uinta Basin, and coordinating with EP’s customers on prices in the Texas Eagle Ford region. The penalty is the largest gun-jumping penalty in US history (A&O Shearman, January 10, 2025; Mayer Brown, January 2025; Bracewell, January 2025).

At 94 days of violation and $51,744 per-day cap then in effect, statutory maximum exposure exceeded $4.86 million per violator; the settled $5.68 million was shared across the three entities. The XCL case is the most aggressive gun-jumping enforcement in HSR Act history and establishes a clear monetary precedent for parties tempted to coordinate during the waiting period.

12.3 The September 18, 2024 Ryan Cohen / GameStop / Wells Fargo Failure-to-File Penalty

On September 18, 2024, the FTC announced that Ryan Cohen, CEO and chairman of GameStop, agreed to a near-$1 million civil penalty to settle charges that his acquisition of Wells Fargo voting securities violated the HSR Act (Wilson Sonsini, September 2024). The acquisition occurred March 2018 through March 2020; Cohen filed a corrective HSR notification on January 14, 2021, nearly three years after the violation began.

The Cohen case is a clean example of executive-equity-compensation and passive-investor failure-to-file rather than PE structuring. The case is significant for the sub-threshold tracker because it confirms that the FTC will pursue civil penalties even on transactions where competition harm is essentially zero, signaling that the deterrent value of HSR enforcement matters independently of the underlying transaction’s competitive significance.

12.4 The May 23, 2024 Joint FTC / DOJ Serial Acquisitions RFI

On May 23, 2024, the FTC and DOJ Antitrust Division jointly issued a Request for Information on serial acquisitions and roll-up strategies (Morrison & Foerster alert, June 4, 2024). The agencies invited public comment on transactions whose competitive significance is masked by sub-HSR sizing. The RFI did not result in rulemaking during the Biden administration’s remaining tenure.

Under the Ferguson FTC the RFI has not been rescinded, but as of June 2026 no formal rulemaking has followed. The RFI’s evidentiary record is now part of the agency’s institutional file and could be used to support future rulemaking or enforcement decisions on aggregation rules.

12.5 DOJ Antitrust Division HSR Enforcement 2024-2026

DOJ HSR enforcement focuses primarily on gun-jumping and HSR violations in industries within DOJ jurisdiction, including banking, telecommunications, agriculture, and defense. Public 2024-2026 DOJ HSR cases of note include the Hewlett Packard Enterprise / Juniper Networks Section 7 challenge filed January 30, 2025, which consolidated with HSR review rather than acting as a standalone HSR-violation case. General prior-approval and prior-notice usage in 2024-2025 DOJ consent decrees has continued in transportation and agriculture sectors (Akin Gump Antitrust Deal Diary Q1 2025).

Confidence: HIGH on the XCL and Cohen cases, the 2024 RFI, and the DOJ enforcement summary; MEDIUM on the 2026 daily penalty cap, which depends on a pending Federal Register notice.

13. Welsh Carson May 13, 2025: First Sponsor-Level Prior-Approval Remedy

13.1 Filing and Procedural History

On September 21, 2023, the FTC filed FTC v. US Anesthesia Partners, Inc. and Welsh, Carson, Anderson & Stowe, et al., No. 4:23-cv-03560 (S.D. Tex.) (FTC Matter No. 2010031). The complaint alleged that USAP and Welsh Carson engaged in a multi-year scheme to roll up nearly every large anesthesia practice in Texas to create a single dominant provider, with the resulting market dominance used to demand higher prices.

The USAP case marked the first time in the FTC’s 110-year history that the Commission filed a federal complaint targeting a sub-threshold roll-up program at the PE sponsor level. The complaint named Welsh Carson directly as a defendant alongside the USAP portfolio company, alleging that the sponsor itself was a moving party in the consolidation strategy.

13.2 The Welsh Carson Consent Order

Welsh Carson reached a proposed consent agreement with the FTC, published for public comment at 90 FR 9709 on February 18, 2025 (90 FR 9709, Welsh Carson Analysis of Agreement Containing Consent Order to Aid Public Comment). The Commission approved the final consent order on May 13, 2025 (FTC Approves Final Order with Welsh Carson, May 2025).

Key terms of the final order:

• Prior approval from the FTC for any future Welsh Carson investments in anesthesia anywhere in the United States.
• Prior approval for certain acquisitions by any majority-owned Welsh Carson anesthesia group anywhere in the United States.
• 30 days advance notice for certain transactions involving other hospital-based physician practices.
• 19.99% passive equity cap on any future Welsh Carson position in any US anesthesia entity, with no board seat and no operational control rights.
• 10-year compliance period with regular compliance reports.
• No admission of liability and no monetary penalty.

The order is the first federal precedent extending a prior-approval remedy to a private equity sponsor separately from its portfolio company. Chair Andrew Ferguson and Commissioner Melissa Holyoak issued a concurring statement noting that the antitrust analysis would be the same if Welsh Carson were, for example, an individual or institutional investor, signaling that the new FTC leadership does not treat PE ownership as a separate analytical category (Katten Muchin Rosenman summary of Welsh Carson settlement; Mondaq summary).

13.3 USAP April 22, 2026 Settlement Update

The FTC announced an agreement in principle to settle the USAP portion of the litigation on April 22, 2026 (FTC Charts Path to Restore Competition in Texas Anesthesia Markets in USAP Litigation). Final consent order terms were still being finalized as of the date of this report. The settlement does not require USAP to admit wrongdoing (Healthcare Dive, April 2026 coverage).

13.4 Significance for Sub-Threshold Structuring

The Welsh Carson consent order is the most important development for HSR threshold avoidance enforcement since the 1976 Act. By requiring prior approval at the sponsor level for future sub-threshold acquisitions, the FTC obtained a tool that does not depend on the HSR size-of-transaction test at all. The remedy is fact-and-sponsor-specific (limited to anesthesia and certain other hospital-based physician markets), but it establishes a template the Commission can use in future roll-up cases.

The template, if replicated across dental DSO, dermatology, behavioral health, ophthalmology, veterinary, and home-services verticals, would materially reshape the PE roll-up economics. A sponsor required to obtain prior approval for every future sub-threshold add-on in a designated vertical faces compliance costs and timing delays that approach those of HSR filings, even though no individual transaction crosses the threshold.

The Ferguson FTC’s continuation of the USAP case through the April 22, 2026 settlement signals that the sponsor-level prior-approval remedy is bipartisan in operation, not a Khan-era artifact. The Welsh Carson concurring statement from Ferguson and Holyoak that PE is not a separate analytical category does not change the operational reach of the order itself.

Confidence: HIGH on the consent order terms, FTC public statements, and procedural history.

14. State Baby-HSR Table: 15 Jurisdictions

When federal HSR is not triggered, state-level notification regimes increasingly are. At least 15 states have enacted healthcare-specific or general premerger notification statutes effective in 2024 through 2027. The cross-reference is Wave 10 State AG Healthcare PE Enforcement Tracker, which provides per-state AG office contacts and 2024-2026 case docket.

14.1 General Cross-Industry Baby HSR Regimes

14.2 Healthcare-Specific State Premerger Notification

14.3 The Below-HSR-But-Above-State-Threshold Sweet Spot

The structural consequence of the state-level patchwork is that PE platforms structuring sub-HSR deals now face state-level notification in 15-plus jurisdictions, with no floor at all in Washington (for WA-based parties), New York, Illinois, and Connecticut. The sweet spot of a transaction that escapes both HSR and any state-level regime is shrinking. In healthcare, the empirical reality as of June 2026 is that any transaction touching California, Colorado, New York, Massachusetts, Illinois, Washington, Oregon, Indiana, Minnesota, Connecticut, Nevada, New Mexico, Rhode Island, Maryland, or Vermont in any material respect must clear at least one state-level filing regardless of HSR status.

For non-healthcare sectors, only Washington (HB 1607 cross-industry interpretation), Colorado (HB 24-1308), and California (SB 25 effective January 1, 2027) have general baby HSR statutes that pick up cross-industry transactions. The non-healthcare sub-HSR M&A market remains substantially unmonitored.

The CA SB 351 reference in some 2026 secondary sources is sometimes confused with CA SB 25; the operative California cross-industry baby HSR statute is SB 25, signed February 10, 2026, effective January 1, 2027. SB 351 is the parallel California Corporate Practice of Medicine reform package separately tracked under CT Acquisitions Wave 10.

Confidence: HIGH on statute identification and effective dates; MEDIUM on threshold mechanics for individual states because each has multiple sub-rules.

15. Academic Literature on Sub-Threshold M&A

15.1 Wollmann 2019: Stealth Consolidation (American Economic Review: Insights)

Thomas G. Wollmann, “Stealth Consolidation: Evidence from an Amendment to the Hart-Scott-Rodino Act,” American Economic Review: Insights, 1(1): 77-94 (June 2019) (AER:I 2019). The paper exploits the 2001 increase in the HSR size-of-transaction threshold from $15 million to $50 million as a natural experiment. Wollmann shows:

• Newly exempt deals received antitrust investigations approaching zero.
• Mergers between competitors rose sharply in the newly exempt zone.
• The rise was due to firms endogenously responding to reduced premerger scrutiny.

The paper won the 2020 Best Paper Award from the Association of Competition Economics and the Jerry S. Cohen Award. It is the foundational empirical citation for the stealth consolidation thesis.

15.2 Wollmann 2020: How to Get Away with Merger (NBER 27274)

Thomas G. Wollmann, “How to Get Away with Merger: Stealth Consolidation and Its Effects on US Healthcare,” NBER Working Paper 27274 (May 2020) (NBER 27274). The paper extends the 2019 work specifically to US dialysis. Wollmann shows:

• Exempt dialysis mergers almost completely avoid enforcement.
• Exempt mergers materially increase market concentration.
• Patient outcomes (hospitalization and mortality) deteriorate in markets affected by exempt mergers.

A structural model simulates the equilibrium response of removing exemptions; Wollmann concludes that benefits exceed costs. The NBER paper is the second of the two Wollmann citations that anchors every Senate Antitrust Subcommittee briefing on sub-threshold M&A in 2024 and 2025.

15.3 Cunningham, Ederer, Ma 2021: Killer Acquisitions (Journal of Political Economy)

Colleen Cunningham, Florian Ederer, and Song Ma, “Killer Acquisitions,” Journal of Political Economy 129(3): 649-702 (March 2021) (JPE 2021). The paper studies the pharmaceutical industry and shows:

• Incumbent firms sometimes acquire innovative targets primarily to discontinue the target’s projects, the killer acquisition pattern.
• Acquired drug projects are less likely to be developed when they overlap with the acquirer’s portfolio.
• 5.3 to 7.4 percent of pharmaceutical acquisitions in the sample qualify as killer acquisitions.
• Killer acquisitions disproportionately occur just below thresholds for antitrust scrutiny.

Awards: Jerry S. Cohen Award for Antitrust Scholarship; Robert F. Lanzillotti Prize; AdC Competition Policy Award. The just-below-threshold bunching empirical finding is the most-cited single result in 2024-2025 FTC speeches and Senate Antitrust hearing testimony on sub-HSR M&A.

15.4 ABA Antitrust Section and ABA Health Law Section Reference Works

The ABA Antitrust Section Premerger Notification Practice Manual, 6th edition (2023), is the practitioner gold-standard reference. The Manual contains the most current synthesis of FTC PNO informal interpretations, formal interpretations, and case law through the publication date.

The ABA Health Law Section, “State Pre-Merger Notification Requirements for Healthcare Transactions” (August 2025) (ABA Health Law Section state survey) is the most comprehensive consolidated tracker of state baby HSR statutes through August 2025.

15.5 American Antitrust Institute and Open Markets Institute Positions

The American Antitrust Institute has filed multiple amicus briefs in 2024-2026 supporting more aggressive sub-threshold enforcement, including in the USAP litigation. The Open Markets Institute has produced policy white papers on sub-HSR PE roll-ups in healthcare, home services, and veterinary medicine, with research drawn directly from the PESP and Capitol Forum data sets. Both institutions feed directly into the Senate Antitrust Subcommittee record and Khan FTC alumni network.

Confidence: HIGH on all citations.

16. The Stealth Consolidation Thesis: From Dialysis to PE

The Wollmann 2019 and 2020 papers established the empirical foundation: when a federal pre-merger notification regime exempts sub-threshold transactions, the share of competitor-to-competitor mergers in the exempt zone rises sharply, and downstream concentration and quality metrics deteriorate. The original 2001 natural experiment was thirty-fold in size: the threshold moved from $15 million to $50 million, and Wollmann documented the response.

The 2020-2026 thresholds, by contrast, have moved 42 percent in five years, from $94 million in 2020 to $133.9 million in 2026, without any single dramatic step. The cumulative effect is comparable to the 2001 reset in magnitude. The PE add-on model maps directly onto Wollmann’s empirical setup: each add-on is competitor-to-competitor consolidation in the local market, at sub-threshold value, with negligible federal review. The Cunningham-Ederer-Ma 2021 bunching finding (acquisitions cluster just below the threshold) extends the thesis from dialysis to pharmaceuticals and, by implication, to any concentrated services vertical where sub-threshold M&A is plausible.

The dental DSO case provides the most direct PE extension of Wollmann’s dialysis finding. Heartland Dental, Aspen Dental Management, Smile Brands, and the 50-plus smaller DSO platforms collectively control thousands of US dental offices through serial sub-threshold add-ons. The Senate Antitrust Subcommittee’s 2024 staff briefing on dental DSO consolidation cited Wollmann directly in arguing that the dialysis pattern is reproducing in dentistry.

The veterinary case is the second-cleanest extension. The 2020 NVA / Compassion First FTC enforcement, requiring divestitures of seven specialty veterinary hospitals to MedVet, established that local-market concentration in veterinary services can be competitively meaningful at the metropolitan area level. Subsequent serial add-ons by VetCor, PetVet Care Centers, and the now-Ethos-owned NVA continue the pattern below the threshold.

The home-services case is the most novel extension. Apex Service Partners, Wrench Group, Sila Services, Service Logic, Redwood Services, Champions Group, and SPS PoolCare each operate the same architectural pattern: HSR-reportable platform creation, then sub-threshold add-on streams that dwarf the platform creation in count. The home-services case has not yet drawn federal enforcement action and may not, given the lower price-elasticity of demand and lower per-customer price impact of local concentration. But the same Wollmann-type concentration mechanism applies.

The Capitol Forum Tarbell coverage of USAP / Welsh Carson throughout 2023-2026 explicitly framed the case as a Wollmann-style test of whether the federal antitrust apparatus can reach sub-threshold roll-ups at all. The Welsh Carson consent order answers in the affirmative for at least one PE sponsor in at least one vertical, through the prior-approval remedy described in Section 13 above.

Confidence: HIGH on the academic citations and the FTC enforcement record; MEDIUM on the cross-vertical extension of the dialysis result, which is by analogy rather than per-vertical empirical replication.

17. Six Counter-Narrative Findings

17.1 The Stealth Consolidation Thesis Holds Up

The Wollmann (2019, 2020) and Cunningham-Ederer-Ma (2021) papers provide the empirical backbone for the policy claim that the HSR threshold is too high to catch competitively meaningful M&A. The FY 2024 federal data (1,973 reportable filings) versus the PESP 2024 add-on count (621 healthcare add-ons alone) is consistent with that thesis. The structural ratio of unreported to reported transactions is at least 1:1 in healthcare alone, and likely 3:1 to 8:1 or higher across all sectors.

17.2 The Serial Acquirer Pattern Is Quantifiable

Sponsor-level deal counts in 2024-2025 documented in this report include: Apex Service Partners approximately 60 add-ons in 2025; VetCor targeted 100-plus annually; SPS PoolCare 191 cumulative by January 2026; Heartland Dental multiple per quarter; LifeStance quarterly tuck-ins disclosed in 10-Qs. Each of these sponsors operates at a scale where the platform itself exceeds $1 billion in revenue or transaction value. None of the constituent sub-threshold deals is individually visible in the federal HSR data.

17.3 State AG Patchwork Is the New Pre-Merger Notification Regime

When HSR is silent and the state regime triggers, the state attorney general becomes the de facto pre-closing antitrust review. New York’s threshold-less material transaction statute, Washington’s no-floor regime for WA-based parties, and California’s broad 2027 baby HSR regime mean that by 2027 a sub-threshold deal touching three or more states with active baby HSR regimes will face notification timeline pressure similar to a small HSR filing. The cumulative compliance burden has shifted from federal to state. CT Acquisitions Wave 10 State AG Healthcare PE Enforcement Tracker provides the per-state docket.

17.4 The 2024 HSR Form Revision Would Have Closed Some Loopholes

The vacated Final Rule required identification of all minority investors above five percent, prior acquisitions in the same NAICS code, and overlapping board memberships. These additions would have materially increased the federal field of view into PE platform structure. Their reversal in February 2026 returned the federal antitrust agencies to a 2023-era visibility profile.

17.5 Aggregation Rule Loophole Through Distinct UPEs

The non-aggregation rule across distinct UPEs is what enables serial sub-threshold add-on roll-ups. The agencies have not attempted to challenge this in 2024-2026 because the rule is set at the regulatory level (16 CFR 801.13) and any change would require formal rulemaking. The 2024 RFI on serial acquisitions opened the door to a rulemaking but no proposal was published before the Biden FTC’s tenure ended. Under the Ferguson FTC, the RFI record exists but no formal rulemaking has followed.

17.6 The Welsh Carson Template Is Replicable

The Welsh Carson sponsor-level prior-approval order applies only to anesthesia and certain hospital-based physician practices. As an enforcement template, it is replicable to any vertical where the FTC can document a multi-year roll-up program with measurable price effects. Dental DSO, dermatology, behavioral health, ophthalmology, and veterinary medicine all have publicly documented pricing literature that could anchor a follow-on case. The Ferguson FTC’s continuation of the USAP case through April 22, 2026 settlement, and the bipartisan Welsh Carson concurring statement, suggest the template will survive across administrations.

Confidence: HIGH on rule mechanics; MEDIUM on the policy direction under the Ferguson FTC; MEDIUM on the replicability of the Welsh Carson template across verticals.

18. PE-Specific Dimensions and Cross-Wave Linkages

18.1 Platform Creation Above, Add-Ons Below

The standard PE healthcare and services thesis is: platform creation at HSR-reportable size (which triggers FTC review and clears it), then three to five years of sub-threshold add-ons that never trigger HSR. KKR’s Heartland Dental acquisition (March 2018, undisclosed but well above $1 billion) cleared HSR, and the seven-plus years of subsequent add-ons (continuing through 2025-2026) have been sub-threshold. The same architecture holds for Apex Service Partners under Alpine then Apollo, Wrench Group under Leonard Green, and Aspen Dental Management under American Securities then Ares plus Leonard Green.

The CT Acquisitions Wave 12 Sponsor Concentration tracker provides the per-sponsor concentration profile that lets buyers and policy analysts identify which sponsors run multiple platforms in the same vertical or geographic market. The Wave 12 tracker also flags sponsors whose cumulative sub-threshold add-on count crosses regulatory inflection points (typically 50-add-on and 100-add-on count thresholds where state AG attention starts).

18.2 Single-Family Offices Operate Below HSR by Default

Cross-reference Wave 11 Top 200 single-family office (SFO) tracker. SFOs typically do not have the platform-creation transaction problem at all because they invest direct or through co-investment structures that often stay below the HSR threshold per deal. The SFO model is structurally compatible with HSR avoidance for the same reason PE add-ons are: distinct UPEs, sub-threshold per transaction.

The Wave 11 tracker documents that the top-200 SFOs by AUM completed an estimated 1,800 direct private-company investments in calendar 2024, of which fewer than 30 were HSR-reportable. The SFO contribution to sub-threshold M&A volume is at least as large as the PE add-on contribution in absolute count terms, and may exceed it in calendar 2024 across all sectors.

18.3 GP-Led Continuation Vehicle Structures and 802.30

Cross-reference Wave 8 GP-led continuation vehicle tracker and Wave 12 CV Discount tracker. GP-led continuation funds where the same general partner continues to control the portfolio company under a new fund vehicle can in principle qualify for 16 CFR 802.30 intra-person exemption analysis, provided no new ultimate economic owner is brought in at 50 percent or more. The FTC PNO has not issued comprehensive guidance on continuation vehicle reportability in the 2024-2026 window.

The Wave 12 CV Discount tracker quantifies the typical NAV discount applied to portfolio companies rolled into CVs (median 8.5 percent in 2025, ranging from 3 percent to 22 percent depending on fund vintage and portfolio composition). The discount mechanism is independent of HSR but interacts with it: a CV closing at a discounted NAV may fall below the HSR threshold at the transaction-value test even where the underlying portfolio is well above.

18.4 Failed Take-Privates Above HSR But Failing at Second Request

Cross-reference Wave 10 PE failure tracker. The FY 2024 HSR Annual Report’s 59 second requests and 32 enforcement actions include several PE take-privates that triggered HSR and failed at the second request stage. The pattern is the inverse of the sub-threshold add-on pattern: above the threshold, large PE deals can be blocked; below the threshold, small PE add-ons cannot. The Wave 10 failure tracker quantifies the failure rate for 2024-2026 PE take-privates above $5 billion at approximately 12 percent at the second-request stage, with 22 percent of those proceeding to litigation.

18.5 The Sponsor-Side Trigger That Replaces HSR: State AG Notification

For PE sponsors operating below the federal HSR threshold but inside one of the 15 state baby-HSR jurisdictions, the trigger has moved from HSR to the state AG office. Healthcare PE sponsors in 2026 routinely file with two to four state AGs per add-on transaction even where no federal filing is required. The CT Acquisitions Wave 10 State AG Healthcare PE Enforcement Tracker documents the 2024-2026 state AG enforcement record by state.

Confidence: MEDIUM on cross-wave linkages, MEDIUM on the empirical magnitudes cited from each cross-wave tracker.

19. Historical HSR Threshold Context 1976-2026

19.1 1976 Statute and 1978 First Threshold

The Hart-Scott-Rodino Antitrust Improvements Act was signed September 30, 1976. The original size-of-transaction threshold was $15 million. The original size-of-person test was $10 million / $100 million. The Act was the most significant amendment to US antitrust pre-merger review since the Clayton Act 1914.

19.2 The 2001 Statutory Reset

The 21st Century Department of Justice Appropriations Authorization Act 2000 (Public Law 106-553) raised the size-of-transaction threshold to $50 million and introduced annual GNP-based indexing for the first time. The 2001 reset is the natural experiment that Wollmann (2019) exploits to identify the stealth consolidation effect. The 2001 reset was the first major HSR threshold change in 23 years, equivalent in real terms to roughly tripling the threshold once 1976-2000 inflation is netted out.

19.3 The 2022 Merger Filing Fee Modernization Act

The Merger Filing Fee Modernization Act of 2022 (Public Law 117-328 Division GG, December 29, 2022) restructured filing fees into six size-tiered brackets with fees ranging from $30,000 (smallest reportable) to $2.46 million (largest, $5.36B+ in 2026). The fee tiers, but not the size-of-transaction notification threshold, are now indexed annually. The MFFMA was the first material modernization of the HSR filing fee structure since the original 1990s tiering.

19.4 The 2024 HSR Form Revision

The October 10, 2024 Final Rule was the largest HSR Form revision since 1978. It was vacated February 12, 2026 (Chamber of Commerce v. FTC). The appeal is in abeyance through December 31, 2026 (Fifth Circuit order, May 26, 2026). The replacement rulemaking process is in early stages at the Ferguson FTC as of June 2026.

Confidence: HIGH.

20. Khan FTC Versus Ferguson FTC: PE Jurisdictional Handoff

Chair Lina M. Khan’s FTC (June 15, 2021 to January 20, 2025) pursued the most aggressive sub-threshold and PE-roll-up enforcement program in US antitrust history. Khan-era milestones bearing on sub-threshold M&A include:

• The 2021 prior-approval policy revival, restoring a tool the Reagan and Trump-I FTCs had abandoned.
• The USAP / Welsh Carson complaint (September 21, 2023), the first sub-threshold roll-up complaint naming a PE sponsor directly.
• The 2024 HSR Form revision Final Rule (October 10, 2024), the largest Form change since 1978.
• The May 23, 2024 joint serial-acquisitions RFI.
• The August 2024 publication of the Khan FTC PE healthcare hearings record.

Chair Andrew N. Ferguson (January 20, 2025-present) has signaled in the Welsh Carson concurring statement and panel remarks that PE is not a separate analytical category. Ferguson and Holyoak’s concurring statement in Welsh Carson explicitly framed the case as one where Welsh Carson was the buyer, not as a PE-specific enforcement matter (FTC Statement on Welsh Carson, January 2025 update; Mondaq summary).

The Ferguson FTC’s first-year enforcement record bearing on sub-threshold M&A:

• Welsh Carson consent order finalized May 13, 2025 (continued from Khan FTC).
• HSR Form Final Rule vacated by E.D. Tex. February 12, 2026; Fifth Circuit appeal pause May 26, 2026 (not Ferguson FTC decision; federal litigation outcome).
• USAP settlement announced April 22, 2026 (continued from Khan FTC).
• RFI on serial acquisitions not rescinded but no proposed rulemaking published.
• Replacement HSR Form rulemaking in early stages.

The handoff has produced operational continuity on sub-threshold enforcement (USAP and Welsh Carson cases continued without interruption) but procedural reset on rulemaking (HSR Form revision rolled back through litigation, with replacement still pending). The first-year enforcement focus has been somewhat re-weighted toward labor markets and tech-platform behavior versus the Khan FTC’s healthcare and PE focus, though the USAP and Welsh Carson cases have continued under Ferguson without modification.

Confidence: HIGH on the chronology and case outcomes; MEDIUM on the policy direction characterization, which is still developing as of June 2026.

21. Limitations and GAP Labels

Three GAP areas in this report deserve explicit identification.

GAP 1: Smucker-Hostess October 2023. The original prompt characterization of the Smucker-Hostess transaction as an HSR avoidance case is not corroborated. The public record shows that Smucker filed HSR notification, the waiting period expired without a second request, and the deal closed normally. This report labels Smucker-Hostess as a GAP and does not include it in the named sub-threshold deal table.

GAP 2: Per-deal values for sub-threshold add-ons. The named deal tables in Section 7 above include sponsor identities, platform identities, and counts at HIGH confidence, but individual transaction values at LOW confidence. Sponsors are not required to disclose sub-threshold acquisition values under HSR, and rarely disclose them in 10-Q filings except in aggregate. The 60-per-year Apex count, 100-per-year VetCor target, 191-cumulative SPS PoolCare count, and quarterly Heartland Dental count are HIGH confidence in count but LOW in per-deal value.

GAP 3: Continuation vehicle reportability. The FTC PNO has not issued comprehensive 2024-2026 guidance on continuation vehicle reportability. Section 802.30 intra-person exemption analysis is fact-specific, and the CT Acquisitions Wave 8 GP-led continuation vehicle tracker treats individual CV transactions at MEDIUM confidence for HSR treatment. This report cites Wave 8 for further detail but does not attempt per-CV HSR analysis.

Three further limitations are worth noting. The FY 2025 HSR Annual Report had not been released as of June 22, 2026; the FY 2025 numbers in this report are estimates pending the official release expected fall 2026. The 2026 maximum daily civil penalty figure is also pending Federal Register publication. The full Ferguson FTC policy direction on sub-threshold rulemaking is still developing and may shift before December 31, 2026 when the Fifth Circuit abeyance expires.

Confidence: HIGH on the GAP identifications themselves.

22. Related CT Acquisitions Research

• Wave 12 Sponsor Concentration Tracker: per-sponsor concentration profile, cumulative add-on count by sponsor, regulatory inflection point flagging. Cross-link to Sections 8, 9, 10, 11, 18.
• Wave 12 CV Discount Tracker: GP-led continuation vehicle NAV discounts, 2024-2026 transactions, and HSR 802.30 analysis. Cross-link to Section 18.3.
• Wave 11 Top 200 Single Family Office Tracker: SFO direct investment volumes and the structural compatibility with sub-HSR M&A. Cross-link to Section 18.2.
• Wave 10 State AG Healthcare PE Enforcement Tracker: per-state baby HSR docket, 2024-2026 enforcement record, AG office contacts. Cross-link to Section 14 and Section 17.3.
• Wave 10 PE Failure Tracker: 2024-2026 PE take-private failures at HSR second-request stage. Cross-link to Section 18.4.
• Wave 9 Home Services PE Roll-Up Tracker: per-platform documentation for Apex, Wrench, Sila, Service Logic, Redwood, Champions, SPS PoolCare. Cross-link to Sections 7.3, 8, 10.
• Wave 8 GP-Led Continuation Vehicle Tracker: per-CV documentation, HSR 802.30 analysis. Cross-link to Section 18.3.
• Healthcare PE Vertical Trackers: dental DSO, dermatology, behavioral health, ophthalmology, veterinary, cardiology. Cross-link to Sections 7.1, 7.2, 7.4, 7.5, 11.

23. Sources

23.1 Federal Statutory and Regulatory Primary Sources

• 15 USC 18a (Hart-Scott-Rodino)
• 16 CFR Part 801 (Coverage Rules)
• 16 CFR Part 802 (Exemption Rules)
• 16 CFR Part 803 (Transmittal Rules)

23.2 FTC Federal Register Notices on HSR Thresholds

• 85 FR 4814 (2020 thresholds)
• 86 FR 7870 (2021 thresholds)
• 87 FR 6705 (2022 thresholds)
• 88 FR 5004 (2023 thresholds)
• 89 FR 7609 (2024 thresholds)
• 90 FR 8463 (2025 thresholds)
• 91 FR 2133 (2026 thresholds)
• 89 FR 89216 (HSR Form Final Rule, November 12, 2024)

23.3 FTC HSR Annual Reports to Congress

• FY 2024 HSR Annual Report (September 2025)
• FTC and DOJ FY 2024 HSR Press Release (September 26, 2025)
• FY 2023 HSR Annual Report Press Release (October 2024)

23.4 FTC Enforcement and Policy

• FTC v. US Anesthesia Partners, Inc. and Welsh Carson docket
• FTC Welsh Carson Settlement Press Release (January 7, 2025)
• Welsh Carson Federal Register Consent Order Notice (February 18, 2025)
• FTC USAP Settlement Press Release (April 22, 2026)
• FTC Welsh Carson Final Order Press Release (May 13, 2025)
• FTC Record Gun-Jumping Penalty XCL / Verdun / EP (January 7, 2025)
• FTC Final HSR Form Revision Release (October 10, 2024)
• FTC 2026 HSR Thresholds Page
• FTC Premerger Notification Program
• FTC When to Aggregate under the HSR Act
• FTC Valuation of Transactions Reportable under the HSR Act
• FTC Formal Interpretation No. 15
• FTC Statement on Prior Approval Provisions (2021)
• FTC Restoring Prior Approval Policy Press Release (October 25, 2021)

23.5 Court Decisions on the HSR Form Revision

• Chamber of Commerce v. FTC, E.D. Tex. Memorandum and Order vacating the HSR Form Final Rule (February 12, 2026), Wilson Sonsini summary
• Fifth Circuit order denying stay pending appeal (March 19, 2026), Foley & Lardner summary
• Fifth Circuit abeyance order (May 26, 2026), Gibson Dunn summary

23.6 Academic Literature

• Wollmann, Thomas G., “Stealth Consolidation: Evidence from an Amendment to the Hart-Scott-Rodino Act,” American Economic Review: Insights 1(1): 77-94 (June 2019)
• Wollmann, Thomas G., “How to Get Away with Merger: Stealth Consolidation and Its Effects on US Healthcare,” NBER Working Paper 27274 (May 2020)
• Cunningham, Colleen, Florian Ederer, and Song Ma, “Killer Acquisitions,” Journal of Political Economy 129(3): 649-702 (March 2021)
• ABA Antitrust Section, Premerger Notification Practice Manual, 6th Edition (2023)
• ABA Health Law Section, “State Pre-Merger Notification Requirements for Healthcare Transactions” (August 2025)

23.7 State Statutes and Tracking Resources

• Washington HB 1607 (2019)
• Washington HB 2548 (2026)
• Colorado HB 24-1308 / HB 25 transitional
• California SB 25
• Illinois Public Act 103-0526
• Indiana SEA 9 (2024)
• Massachusetts H.5159 (2025)
• Connecticut Public Act 23-171 (HB 6669)
• Oregon SB 951
• New York Article 45-A PHL
• Minnesota SF 4097
• Goodwin State Healthcare Transaction Notification Laws tracker
• Winston & Strawn Survey of State Transaction Notification Requirements (Baby HSR)

23.8 Practitioner Alerts and Surveys

• White & Case “FTC announces annual updates to US HSR thresholds; Highest filing fees now $2.46 million” (January 2026)
• Sidley Austin “US FTC Releases 2026 Thresholds for HSR Act Filings” (January 16, 2026)
• Baker Botts “FTC Revises Merger Filing Fees and Jurisdictional Thresholds” (January 2026)
• Cooley “FTC Issues 2026 HSR Filing Thresholds, Fee Adjustments and Interlocking Directorate Updates” (January 16, 2026)
• Wilson Sonsini “FTC Obtains $1 Million Civil Penalty for HSR Act Violation” (September 2024)
• A&O Shearman “FTC secures record USD5.68 million gun-jumping penalty” (January 2025)
• Clifford Chance “Federal Trade Commission Announces Record US$5.68 Million Fine for Gun-Jumping” (January 2025)
• Morrison & Foerster “FTC and DOJ Enlist the Public in Latest Attack on Serial Acquisition Strategies” (June 4, 2024)
• Katten Muchin Rosenman on Welsh Carson Settlement
• Morgan Lewis “Biden Administration’s HSR Data: 7 Key Takeaways”
• Mayer Brown “Counsel’s Guide to HSR” (2008 historical reference)

23.9 PE Deal-Tracking Sources

• Private Equity Stakeholder Project, “Private Equity Healthcare Deals: 2024 in Review”
• Private Equity Stakeholder Project, “Private Equity Health Care Acquisitions” rolling monthly tracker
• PESP, “Antitrust enforcement and consolidation in veterinary medicine”
• LevinPro Healthcare M&A tracker
• PrivSource Acquisition Deal Tracker
• Behavioral Health Business
• Group Dentistry Now
• Becker’s Dental Review
• SPS PoolCare press releases
• Pool Spa News
• Pipeline On 2026 HVAC PE Tracker

23.10 Congressional and Oversight Materials

• Senator Klobuchar staff, Antitrust Subcommittee materials
• House Judiciary Antitrust hearings on PE and healthcare consolidation (2024-2025)
• Capitol Forum Tarbell coverage of USAP / Welsh Carson (2023-2026)
• The American Prospect coverage of PE healthcare consolidation
• Financial Times, Bloomberg, Bloomberg Law, Reuters Legal, Politico Pro Antitrust ongoing coverage of HSR and Welsh Carson developments

24. FAQ

Related research: for All-in closing costs as % of EV across deal-size band: 12.3% at $5M / 8.3% at $25M / 7% at $50M / 5.9% at $100M / 4.5% at $250M / 3.6% at $500M; the ‘1% rule’ debunked; Houlihan Lokey FY25 $2.39B revenue; HSR 2026 six-tier fee schedule $35K-$2.46M (91 Fed Reg 2133); 27 QofE provider rankings; Lehman formula + Modified Lehman, see the 2024-2026 M&A Closing Cost Breakdown ($5M-$500M EV).

Related research: for $183B global STR market with the distressed-PE consolidation cycle (Vacasa-Casago $128.6M April 30 2025 Steve Schwab CEO; Sonder Chapter 7 Nov 14 2025 post Marriott license termination; NYC LL18 22,246 to ~4,000 listings; Maui Bill 9 Dec 15 2025; Hignell-Stark 5th Cir Oct 7 2025; EU 2024/1028 full compliance May 20 2026), see the 2024-2026 Short-Term + Vacation Rental Management Distressed PE Tracker.

Related research: for $53.9B US HOA management market with 30+ named PE platforms (3 NEW platforms in 18 months: Charlesbank/CMH Nov 18 2024, Alpine/Oakline Sept 25 2025, FFL/Pioneer March 2026; RealManage = American Securities June 2 2022 NOT Apax; KWPMC = Odevo Sept 28 2022; RowCal = Morgan Stanley May 2023; FSV + Associa combined own only 11%; Sascha late-innings thesis tested with tuck-under arbitrage of 5-7x to 13-15x platform exits), see the 2024-2026 HOA + Community Association Management PE Roll-Up Tracker.

Related research: for Total secondary $233B 2025 / GP-led $115-116B / CV-specific $106B Evercore (51% YoY), Vista Cloud Software $5.6B June 2025 at disclosed 5% discount to Q1 2024 NAV (most specific public disclosure), 90%+ GP-led H1 2025 less than 10% discount, LP-portfolio 87% NAV, 5th Cir PFAR vacatur June 5 2024, see the 2024-2026 PE Continuation Vehicle Discount-to-NAV Tracker.

Related research: for 17 named US PE sponsors with 3+ platforms in same vertical (Welsh Carson 8 healthcare platforms with USAP 19.99% cap May 12 2025 = first sponsor-level prior-approval remedy; Linden 7; KKR 6; Carlyle 4-MGA NSM+Hilb+Trucordia+Vantage), 10 vertical heat maps, and the state AG patchwork (CA SB 351 + OR SB 951 + WA HB 2548) as the new pre-merger notification regime, see the 2024-2026 PE Sponsor-by-Vertical Concentration Heat Map.

What is the HSR 2026 size-of-transaction threshold?

$133.9 million, effective February 17, 2026, per 91 Federal Register 2133. The threshold is indexed annually to changes in gross domestic product per Section 7A(a)(2) of the Clayton Act.

How many HSR-reportable transactions were filed in fiscal year 2024?

1,973 (adjusted) reportable transactions were filed in fiscal 2024. The FTC and DOJ issued 59 second requests, a 3.0 percent rate. Source: FTC FY 2024 HSR Annual Report to Congress, released September 2025.

How many PE healthcare add-on acquisitions occurred in calendar 2024?

621 healthcare-only PE add-on acquisitions to 383 unique platform companies, per the Private Equity Stakeholder Project, “Private Equity Healthcare Deals: 2024 in Review.” Approximately 60 percent of all US PE deal volume in 2024 was add-on transactions.

Was the 2024 HSR Form Final Rule vacated?

Yes. Chamber of Commerce of the United States of America v. FTC vacated the Final Rule on February 12, 2026 in the Eastern District of Texas. The Fifth Circuit denied the Commission’s motion for a stay pending appeal on March 19, 2026, then on May 26, 2026 granted the government’s unopposed motion to hold the appeal in abeyance through December 31, 2026. Federal filers in 2026 use the pre-2025 HSR form.

What is the Welsh Carson consent order?

The Welsh Carson consent order, final May 13, 2025, requires Welsh Carson to obtain FTC prior approval for any future US anesthesia investments and caps the sponsor at 19.99 percent passive equity in any future US anesthesia entity, with no board seat and no operational control rights, for a 10-year compliance period. The order is the first federal precedent extending a prior-approval remedy to a private equity sponsor for sub-threshold acquisitions, separately from the portfolio company.

What was the USAP April 22, 2026 settlement?

The FTC announced an agreement in principle to settle the US Anesthesia Partners (USAP) portion of the USAP / Welsh Carson litigation on April 22, 2026. The settlement does not require USAP to admit wrongdoing. Final consent order terms were still being finalized as of the date of this report.

What is the largest HSR gun-jumping penalty?

$5.68 million against XCL Resources Holdings LLC, Verdun Oil Company II LLC, and EP Energy LLC, announced January 7, 2025. The conduct involved pre-merger coordination during a 94-day HSR waiting period on a $1.4 billion oil transaction.

How many serial PE add-ons does Apex Service Partners complete per year?

Approximately 60 disclosed sub-threshold add-ons in calendar year 2025, per Pipeline On 2026 HVAC PE Tracker. The platform sits at approximately $1.3 billion in revenue across approximately 300 businesses.

How many cumulative sub-threshold add-ons has SPS PoolCare completed?

191 cumulative add-ons since the 2021 Storr Group platform creation, including the Pool Troopers acquisition closed January 7, 2026 (16,182 accounts, $57 million separate service revenue). The combined entity operates at approximately $144 million in 2026 run-rate revenue.

Which states have baby HSR pre-merger notification regimes?

At least 15 states have healthcare-specific or general premerger notification statutes effective in 2024 through 2027: California (SB 25 effective January 1, 2027), Colorado (HB 24-1308 effective August 6, 2025), Connecticut, District of Columbia, Hawaii, Illinois, Indiana, Maryland, Massachusetts, Minnesota, Nevada, New Mexico, New York, Oregon (SB 951 effective January 1, 2026), Rhode Island, Vermont, and Washington (HB 1607 plus HB 2548 effective June 11, 2026).

What is the academic foundation for the stealth consolidation thesis?

Wollmann (American Economic Review: Insights 2019) “Stealth Consolidation: Evidence from an Amendment to the Hart-Scott-Rodino Act”; Wollmann (NBER 27274, 2020) “How to Get Away with Merger: Stealth Consolidation and Its Effects on US Healthcare”; and Cunningham, Ederer, and Ma (Journal of Political Economy 2021) “Killer Acquisitions.” The Cunningham-Ederer-Ma paper documents that acquisitions disproportionately occur just below thresholds for antitrust scrutiny.

What is the difference between an HSR add-on and a sub-threshold add-on?

An HSR add-on is a follow-on acquisition by a previously HSR-reportable acquirer that itself exceeds the size-of-transaction threshold of $133.9 million in 2026 (or the applicable threshold in the year of the transaction). A sub-threshold add-on falls below the threshold and is not HSR-reportable. The structural difference is significant: HSR add-ons receive federal pre-merger review at the second request stage; sub-threshold add-ons do not.

Can a PE sponsor be required to pre-clear sub-threshold acquisitions?

Yes, under a federal prior-approval remedy. The Welsh Carson consent order of May 13, 2025 is the first federal precedent. Sponsor-level prior approval applies on top of the HSR notification regime and reaches transactions below the size-of-transaction threshold.

Does the Smucker-Hostess October 2023 transaction belong in a sub-threshold tracker?

No. The Smucker-Hostess transaction was HSR-reportable (well above the 2023 $111.4 million threshold) and the HSR waiting period expired normally. This report labels Smucker-Hostess as GAP.

25. About the Author

This tracker is published by CT Acquisitions, a private equity and antitrust research desk focused on roll-up consolidation, sponsor concentration, state AG enforcement, GP-led continuation vehicles, and single-family office co-investment activity. CT Acquisitions reports cross-reference each other through the Wave series: Wave 8 (GP-led CV tracker), Wave 9 (home-services PE roll-ups), Wave 10 (State AG enforcement and PE failure tracker), Wave 11 (top 200 SFO tracker), and Wave 12 (sponsor concentration and CV discount trackers).

The tracker is updated continuously as FTC and DOJ press releases, Federal Register notices, state baby HSR statutes, and PESP, LevinPro, and PrivSource tracking publications are released. Last updated: June 22, 2026.