Mesirow agreed on August 13, 2026 to buy the plan-level 3(38) business of flexPATH Strategies, its second outsourced-fiduciary acquisition in 101 days. The two deals move Mesirow Fiduciary Solutions from $115.2 billion in assets under management and advisement at March 31 to roughly $164 billion, a 42% jump bought rather than gathered. For plan sponsors the number that matters is not the headline. It is that the entity holding discretion over their investment menu is changing hands, and under ERISA that change is a fiduciary decision the committee has to make on the record.
Key takeaways
- Mesirow Fiduciary Solutions goes from $115.2 billion (March 31, 2026) to about $164 billion across two 2026 deals, LeafHouse in May and flexPATH’s plan-level 3(38) book in August.
- Our arithmetic implies the flexPATH book carries roughly $26 billion in plan-level assets, a figure neither firm disclosed.
- A 3(38) appointment does not travel with a purchase agreement. It requires client consent to assignment under the Advisers Act and a fresh appointment under ERISA Section 402(c)(3).
- The DOL’s proposed alternative-assets safe harbor treats reliance on a 3(38) manager as evidence of prudent process, which raises the stakes on who that manager is after consolidation.
- Committees whose 3(38) closes in Q4 should calendar the re-appointment vote, the updated 408(b)(2) disclosure, and a written fiduciary acknowledgment from the acquiring entity.
What Mesirow actually bought, and the number nobody published
The public record gives three data points and skips the one practitioners want.
Mesirow said in May that its fiduciary platform stood at $115.2 billion as of March 31, 2026, and that the LeafHouse Financial Advisors purchase announced May 4 would add about $23 billion, bringing the platform to roughly $138 billion at close. On August 13 it said the flexPATH deal brings the platform to approximately $164 billion supporting nearly 10,000 financial advisors. Terms were not disclosed on either transaction.
Subtract and the plan-level 3(38) book leaving flexPATH sits near $26 billion. Neither press release states it. It follows from Mesirow’s own two disclosures, and it is the first useful sizing of what changed hands, because flexPATH’s frequently cited $83 billion figure from March 2024 covered a business that has since been taken apart. Great Gray assumed management of the collective investment trusts flexPATH had sub-advised. What Mesirow is buying is the discretion, not the product.
Two caveats belong on that $26 billion. The $138 billion was an expected post-close figure quoted in May, and both deals close on their own timetables, LeafHouse in the third quarter and flexPATH in the fourth. Organic movement between March and August is inside the difference. Treat $26 billion as an order of magnitude that no other published number gives you, not as an audited balance.
Sponsors who want to verify any of this without waiting for a client letter have two public files. Form ADV Part 1 shows an adviser’s regulatory assets under management, its ownership, and its affiliated entities, so the before and after picture of both firms is visible without asking anyone. The plan’s own Form 5500 Schedule C names the covered service provider that received indirect compensation, which is where the change of entity will eventually surface in the plan’s filing history. Pulling both now gives the committee a baseline it can point to later.
The pace deserves its own line. May 4 to August 13 is 101 days. In that window Mesirow contracted for $48.8 billion of assets under management and advisement, which is 30% of the platform it will operate once both deals close. Cerulli projects defined contribution plans will lead all channels in outsourced CIO flows over the next five years at $294 billion. One firm just bought the equivalent of a sixth of that five-year flow projection in a single quarter of deal announcements. Buying a book and winning mandates are different achievements, and the comparison is there to size the shortcut, not to equate them.
Why does a 3(38) acquisition require a committee vote?
Because the appointment was never a vendor contract. It was a fiduciary act, and fiduciary acts do not transfer by assignment.
ERISA Section 3(38) defines an investment manager as a fiduciary who has power to manage plan assets, who is a registered adviser, bank, or insurance company, and who has acknowledged in writing that it is a fiduciary with respect to the plan. The named fiduciary appoints that manager under Section 402(c)(3). When the manager’s entity or control changes, three things need to happen and only one of them is automatic.
Consent to assignment. Advisers Act Section 205(a)(2) requires every advisory contract to provide that no assignment occurs without the client’s consent. A change of actual control of the adviser is treated as an indirect assignment. Acquirers typically solicit consent by negative response, a letter that says the relationship continues unless the client objects within a stated window. That is lawful practice and it is also the moment a plan committee can accidentally re-appoint a fiduciary by staying silent, with nothing in the minutes to show a decision was made.
A written acknowledgment from the surviving entity. The Section 3(38) acknowledgment names an entity. If the acquiring firm is the counterparty going forward, the acknowledgment should come from it in writing, not be inferred from the old agreement.
Updated Section 408(b)(2) disclosure. The covered service provider disclosure has to reflect the new provider, its fiduciary status, and its compensation, and the sponsor has to review it for reasonableness. A change in identity is exactly the trigger the rule was written for.
None of this is exotic. It is the documentation a committee will wish it had if a participant later asks who was managing the lineup during the transition, and it costs one agenda item.
What the DOL’s alternatives proposal does to this layer
The proposed rule the Labor Department published in the Federal Register on March 31, 2026, “Fiduciary Duties in Selecting Designated Investment Alternatives,” follows the August 7, 2025 executive order on access to alternative assets in 401(k) plans. Comments closed June 1 and the Department has signaled it wants a final rule by the end of 2026.
One passage in the proposal matters more to the consolidation story than to the alts story. Where a plan fiduciary reasonably relies on the analysis of an investment manager within the meaning of Section 3(38), the Department says that reliance is indicative of a prudent process. The safe harbor, in other words, leans on the judgment of the outsourced fiduciary layer at the same moment that layer is concentrating.
Sponsors should read that as a two-sided proposition. It lowers the burden of documenting a private-markets sleeve if a qualified 3(38) does the analysis. It also means the identity, independence, and resourcing of that manager become the load-bearing element of the defense. A committee that leaned on flexPATH’s analysis in 2026 and finds itself relying on Mesirow’s in 2027 has changed the thing the safe harbor is built on, whether or not the service agreement looks the same.
We covered the liquidity documentation this raises for sponsors when private markets enter the menu in Private Markets Are Coming to the 401(k) Just as They Gate Redemptions. The redemption behavior that sits underneath those sleeves is tracked in our reporting on Q2 BDC redemptions.
Who manufactures the product when the fiduciary is independent?
flexPATH is a useful case because its own history ran the experiment.
The firm was founded in 2015 and built a business that combined 3(38) discretion with proprietary target-date collective investment trusts. That combination produced the leading litigation of the past decade on outsourced discretion. In Lauderdale v. NFP Retirement, participants alleged that the plan fiduciaries breached their duties by selecting and retaining flexPATH’s affiliated target-date funds. Judge James Selna of the Central District of California ruled for the defense on February 23, 2024, after a nine-day bench trial, finding the sponsor acted appropriately in hiring flexPATH and in monitoring it afterward.
The defense verdict settled the case. It did not settle the structural question, and the market answered it commercially. flexPATH’s CIT sub-advisory moved to Great Gray. The plan-level discretion is moving to Mesirow. The manufacture of the product and the exercise of fiduciary discretion over the menu ended up in different companies.
That separation is the quiet argument for what happens next. The DOL proposal invites private-market strategies into designated investment alternatives, and those strategies come from firms with strong distribution incentives. An outsourced 3(38) with no product to sell is a cleaner place for that decision to sit than one with a shelf to fill. Sponsors evaluating a post-merger 3(38) should ask what the acquirer manufactures, because the answer changes the conflicts inventory the committee has to keep.
The same tension played out in the target-date market itself when collective trusts passed mutual funds on the way to 54% of assets, which we examined in Target-Date CITs Hit 54% of Assets as Mutual Funds Lose the 401(k).
Is outsourced fiduciary consolidation good for small plans?
For plans below roughly $50 million it probably is, on price and on access.
Cerulli expects outsourcing assets to reach $5.6 trillion by the end of the decade, a 10.6% annual growth rate, with $1.3 trillion of that from first-time adopters through 2029. Scale in this business shows up in fee schedules and in the depth of the investment team behind a lineup, both of which small plans struggle to buy on their own. A $164 billion platform can staff private-markets diligence that a $2 billion regional 3(38) cannot.
The cost sits in the concentration itself. When two of the larger independent plan-level 3(38) books land inside one firm in the same year, sponsors lose alternatives at exactly the point the DOL is telling them to lean on a 3(38)’s analysis. Benchmarking gets harder when the peer set shrinks. Fee negotiation gets harder when the incumbent knows the switching cost includes re-papering every plan.
Switching costs are the part committees tend to underestimate. Replacing a plan-level 3(38) means a new investment policy statement, a new fiduciary acknowledgment, a fresh 408(b)(2) package, a mapping exercise if the model portfolios differ, and participant notices with their own timing rules. A committee that decides in November it wants out of a book it never chose will spend two quarters getting there. That asymmetry is why the re-appointment conversation is worth having while the deal is still pending rather than after it closes.
There is also a service continuity question that no press release answers. LeafHouse brought the FlexFiduciary and InvestBuild lines and a strategic investment in LeafHouse Financial Services for technology development. flexPATH brings custom portfolio construction and lineup services. Integrating two acquired methodologies into one platform takes time, and during that time the model portfolios inside plans are being maintained by teams whose reporting lines are changing.
What plan committees should do before the Q4 close
The flexPATH transaction is expected to close in the fourth quarter of 2026, and the LeafHouse transaction in the third. Committees affected by either have a two-quarter window to act deliberately rather than by silence.
- Calendar the vote. Put re-appointment of the investment manager on the next committee agenda and record the decision, including the alternatives considered. Consent by non-response is a legal mechanism, not a documented fiduciary process.
- Ask for the acknowledgment in writing from the entity that will hold discretion after close, naming the plan.
- Request the updated 408(b)(2) disclosure and review compensation for reasonableness against at least two competing 3(38) proposals.
- Get the team roster. Names of the people responsible for the lineup before and after close, and what changes at the model-portfolio level.
- Ask the manufacturing question. What products does the acquirer or its affiliates manage that could enter the menu, and how are those conflicts controlled?
Sponsors running an in-plan income or private-markets project alongside this should sequence the fiduciary paperwork first. We looked at the parallel documentation demands of guaranteed income in Vanguard and TIAA Put a Pension Back Inside the 401(k).
Questions to bring to the committee
Two questions get to the point faster than a full vendor review.
If our 3(38) manager changed identity tomorrow, what document in our file shows the committee decided to keep it, and on what basis?
If the DOL finalizes the safe harbor and our 3(38) recommends a private-markets sleeve in 2027, does that recommendation come from a firm that manufactures private-markets product, and would we know?
Figures as of August 17, 2026. Asset totals are as disclosed by Mesirow at each announcement; the implied $26 billion attributed to the flexPATH plan-level book is our calculation from those disclosures and is not a reported figure.
About Me
Founder and Chief Research Analyst at Trading Market Signals. Abdelali El Khadmaoui specializes in AI Wealth Intelligence, Wealth Management, Registered Investment Advisors (RIAs), Family Offices, Retirement Planning and Private Credit. He publishes in-depth research and data-driven analysis for financial professionals.
