Vanguard holds 5.12% in Affiliated Managers Group (NYSE: AMG)

Rhea-AI Filing Summary

Affiliated Managers Group Inc Schedule 13G shows Vanguard Portfolio Management beneficially owned 1,368,430 shares of common stock, representing 5.12% as of 03/31/2026. The filing states Vanguard has sole dispositive power over 1,368,430 shares and sole voting power for 8,637 shares. The filing is signed on 04/28/2026.

Insights

Institutional Ownership Analyst

Large passive manager reports a >5% beneficial stake.

Vanguard Portfolio Management reports beneficial ownership of 1,368,430 shares (5.12%) as of 03/31/2026. The position meets the Schedule 13G threshold for passive institutional investors.

Watch filings for any shift to active ownership or Form 13D amendments; timing of any change would appear in subsequent SEC disclosures.

Corporate Governance Specialist

Voting vs dispositive powers are distinct; Vanguard mostly holds dispositive control.

The filing lists sole voting power of 8,637 shares and sole dispositive power of 1,368,430 shares, indicating decision authority over sales but limited direct voting control across the full stake.

Any material change in voting authority or activism would require amended disclosures in later filings.

Key Figures

Shares beneficially owned: 1,368,430 shares Percent of class: 5.12% Sole voting power: 8,637 shares +1 more

4 metrics

Shares beneficially owned 1,368,430 shares Beneficial ownership as of 03/31/2026

Percent of class 5.12% Percent of common stock as of 03/31/2026

Sole voting power 8,637 shares Number of shares with sole voting power

Sole dispositive power 1,368,430 shares Number of shares with sole power to dispose

Key Terms

Schedule 13G, Beneficial ownership, Sole dispositive power, Investment Company Act of 1940

4 terms

Schedule 13G regulatory

"Schedule 13G shows beneficial ownership of 1,368,430 shares"

A Schedule 13G is a formal document that investors file with the government when they acquire a large ownership stake in a company, usually for investment purposes rather than control. It helps keep the public informed about who owns significant parts of a company's shares, which can influence how the company is managed and how investors make decisions. Filing this schedule is important for transparency and understanding the ownership landscape of publicly traded companies.

Beneficial ownership financial

"Amount beneficially owned: 1368430 (b) Percent of class: 5.12%"

Beneficial ownership means the person or entity that actually enjoys the benefits of owning shares or other assets — such as receiving dividends, voting rights, or price gains — even if the legal title is held in another name. For investors it matters because knowing who truly controls and profits from a company reveals who can influence decisions, exposes potential conflicts of interest or hidden concentration of power, and affects transparency and risk in the stock.

Sole dispositive power regulatory

"Sole power to dispose or to direct the disposition of: 1368430"

Sole dispositive power is the exclusive legal authority to decide what happens to a security — for example, whether to sell, transfer, or retain shares — without needing anyone else’s permission. Investors care because it signals who truly controls the economic outcome of an investment: like holding the only key to a safe, the holder can realize gains or losses and may trigger regulatory reporting, insider rules, or influence over corporate ownership.

Investment Company Act of 1940 regulatory

"investment companies registered under the Investment Company Act of 1940"

A U.S. federal law that sets the rulebook for pooled investment vehicles such as mutual funds, exchange-traded funds and similar money managers, requiring them to register with regulators, disclose holdings and fees, limit conflicts of interest, and follow governance standards. It matters to investors because these protections and transparency rules act like a referee and scoreboard, helping people compare funds, trust that managers follow fair practices, and spot hidden costs or risks.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

Affiliated Managers Group Inc

(Name of Issuer)

Common Stock

(Title of Class of Securities)

008252108

(CUSIP Number)

03/31/2026

(Date of Event Which Requires Filing of this Statement)

Check the appropriate box to designate the rule pursuant to which this Schedule is filed:

Rule 13d-1(b)

Rule 13d-1(c)

Rule 13d-1(d)

schemaVersion:

SCHEDULE 13G

CUSIP Number(s): 008252108

1

Names of Reporting Persons

Vanguard Portfolio Management

2

Check the appropriate box if a member of a Group (see instructions)

(a)
(b)

3

Sec Use Only

4

Citizenship or Place of Organization

PENNSYLVANIA

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 8,637.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 1,368,430.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

1,368,430.00

10

Check box if the aggregate amount in row (9) excludes certain shares (See Instructions)

11

Percent of class represented by amount in row (9)

5.12 %

12

Type of Reporting Person (See Instructions)

IA

Comment for Type of Reporting Person: In accordance with SEC Release No. 34-39538 (January 12, 1998), this Schedule 13G reflects the securities beneficially owned, or deemed to be beneficially owned, by Vanguard Portfolio Management LLC and the following affiliates of Vanguard Portfolio Management LLC or business divisions of such affiliates: Vanguard Fiduciary Trust Company and Vanguard Global Advisers, LLC. This Schedule 13G includes securities held by Vanguard funds, or sleeves thereof, over which Vanguard Portfolio Management LLC exercises dispositive power, in addition to securities held by clients over which the affiliates or business divisions of such affiliates indicated above exercise dispositive and/or voting power. This Schedule 13G does not include securities, if any, beneficially owned by other subsidiaries or affiliates of Vanguard Portfolio Management LLC, or business divisions of such subsidiaries whose ownership of securities is disaggregated from that of the reporting business unit in accordance with such release.

SCHEDULE 13G

Item 1.
(a)	Name of issuer: Affiliated Managers Group Inc
(b)	Address of issuer's principal executive offices: 600 Hale Street, Prides Crossing, MA, 01965
Item 2.
(a)	Name of person filing: Vanguard Portfolio Management
(b)	Address or principal business office or, if none, residence: 100 Vanguard Blvd,, Malvern, PA, 19355
(c)	Citizenship: PA
(d)	Title of class of securities: Common Stock
(e)	CUSIP Number(s): 008252108
Item 3.	If this statement is filed pursuant to §§ 240.13d-1(b) or 240.13d-2(b) or (c), check whether the person filing is a:
(a)	Broker or dealer registered under section 15 of the Act (15 U.S.C. 78o);
(b)	Bank as defined in section 3(a)(6) of the Act (15 U.S.C. 78c);
(c)	Insurance company as defined in section 3(a)(19) of the Act (15 U.S.C. 78c);
(d)	Investment company registered under section 8 of the Investment Company Act of 1940 (15 U.S.C. 80a-8);
(e)	An investment adviser in accordance with § 240.13d-1(b)(1)(ii)(E);
(f)	An employee benefit plan or endowment fund in accordance with § 240.13d-1(b)(1)(ii)(F);
(g)	A parent holding company or control person in accordance with § 240.13d-1(b)(1)(ii)(G);
(h)	A savings associations as defined in Section 3(b) of the Federal Deposit Insurance Act (12 U.S.C. 1813);
(i)	A church plan that is excluded from the definition of an investment company under section 3(c)(14) of the Investment Company Act of 1940 (15 U.S.C. 80a-3);
(j)	A non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J). If filing as a non-U.S. institution in accordance with § 240.13d-1(b)(1)(ii)(J), please specify the type of institution:
(k)	Group, in accordance with Rule 240.13d-1(b)(1)(ii)(K).
Item 4.	Ownership
(a)	Amount beneficially owned: 1368430
(b)	Percent of class: 5.12 %
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: 8637
	(ii) Shared power to vote or to direct the vote: 0
	(iii) Sole power to dispose or to direct the disposition of: 1368430
	(iv) Shared power to dispose or to direct the disposition of: 0
Item 5.	Ownership of 5 Percent or Less of a Class.
	Not Applicable
Item 6.	Ownership of more than 5 Percent on Behalf of Another Person.
	If any other person is known to have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, such securities, a statement to that effect should be included in response to this item and, if such interest relates to more than 5 percent of the class, such person should be identified. A listing of the shareholders of an investment company registered under the Investment Company Act of 1940 or the beneficiaries of employee benefit plan, pension fund or endowment fund is not required. Vanguard Portfolio Management, including investment companies registered under the Investment Company Act of 1940 and other managed accounts, have the right to receive or the power to direct the receipt of dividends from, or the proceeds from the sale of, the securities reported herein.No one other person's interest in the securities reported herein is more than 5%.
Item 7.	Identification and Classification of the Subsidiary Which Acquired the Security Being Reported on by the Parent Holding Company or Control Person.
	Not Applicable
Item 8.	Identification and Classification of Members of the Group.
	Not Applicable
Item 9.	Notice of Dissolution of Group.
	Not Applicable

Item 10.

Certifications:

By signing below I certify that, to the best of my knowledge and belief, the securities referred to above were acquired and are held in the ordinary course of business and were not acquired and are not held for the purpose of or with the effect of changing or influencing the control of the issuer of the securities and were not acquired and are not held in connection with or as a participant in any transaction having that purpose or effect, other than activities solely in connection with a nomination under § 240.14a-11.

SIGNATURE

After reasonable inquiry and to the best of my knowledge and belief, I certify that the information set forth in this statement is true, complete and correct.

Vanguard Portfolio Management

Signature:	Ashley Grim
Name/Title:	Head of Global Fund Administration
Date:	04/28/2026

FAQ

How many AMG shares does Vanguard report owning?

Vanguard reports beneficial ownership of 1,368,430 shares. The Schedule 13G lists 1,368,430 shares of Affiliated Managers Group common stock, representing 5.12% as of 03/31/2026.

What percentage of AMG is owned by Vanguard Portfolio Management?

Vanguard holds 5.12% of AMG's common stock. The filing states that 1,368,430 shares equal 5.12% of the class as of 03/31/2026, meeting the 5% reporting threshold.

Does Vanguard have voting control over all the shares it owns in AMG?

No; Vanguard reports limited voting power relative to dispositive power. The filing shows sole voting power for 8,637 shares and sole dispositive power for 1,368,430 shares, indicating voting authority is narrower than sale/transfer control.

Was the Schedule 13G filing signed and when?

The filing was signed on 04/28/2026. The signature lists Ashley Grim, Head of Global Fund Administration, and the ownership figures are reported as of 03/31/2026.