[SCHEDULE 13D/A] MFS HIGH YIELD MUNICIPAL TRUST SEC Filing

Rhea-AI Filing Summary

Bulldog Investors, LLP and principals Phillip Goldstein and Andrew Dakos report updated ownership stakes in MFS High Yield Municipal Trust (CMU). Based on 25,492,782 common shares outstanding as of May 31, 2025, Bulldog Investors is deemed to beneficially own 3,671,536 shares, or 14.40% of CMU. Phillip Goldstein reports beneficial ownership of 4,007,921 shares, or 15.72%, and Andrew Dakos reports 3,561,726 shares, or 13.97%.

The filing details that Bulldog Investors has sole voting and dispositive power over 109,810 CMU shares and shared power over 3,561,726 shares with its clients, none of whom individually hold more than 5%. Since November 14, 2025, the group bought additional CMU shares, including 215,000 shares on December 12, 2025 at $3.4782 per share and other trades such as 20,000 shares at $3.5083 per share on November 25, 2025. The parties report no special contracts or arrangements regarding CMU beyond these holdings.

Insights

Equity ownership and governance analyst

Goldstein and Dakos report double-digit CMU stakes, signaling a concentrated, actively managed position.

Bulldog Investors, LLP, controlled by Phillip Goldstein and Andrew Dakos, discloses beneficial ownership of 3,671,536 CMU shares, or 14.40% of MFS High Yield Municipal Trust. Goldstein’s reported stake of 4,007,921 shares (15.72%) and Dakos’s 3,561,726 shares (13.97%) indicate a sizable, aligned holding in this closed-end municipal bond fund.

The filing shows recent open-market purchases, including 215,000 shares on December 12, 2025 at $3.4782 per share and other trades around $3.49–$3.51. This pattern suggests continued capital deployment into CMU rather than profit-taking. However, the document does not specify any plans or proposals regarding the fund’s strategy, distribution policy, or structure, so implications for future actions remain undefined.

Ownership percentages are calculated using 25,492,782 CMU shares outstanding as of May 31, 2025, as reported in an N-CSRS. Subsequent disclosures in similar ownership filings would clarify whether these positions continue to grow, stabilize, or decline relative to that baseline.

SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13D

Under the Securities Exchange Act of 1934

(Amendment No. 9)

MFS High Yield Municipal Trust

(Name of Issuer)

Common Stock

(Title of Class of Securities)

59318E102

(CUSIP Number)

Phillip Goldstein
250 Pehle Ave., Suite 708
Saddle Brook, NJ, 07663
914 747-5262

(Name, Address and Telephone Number of Person Authorized to Receive Notices and Communications)

12/12/2025

(Date of Event Which Requires Filing of This Statement)

If the filing person has previously filed a statement on Schedule 13G to report the acquisition that is the subject of this Schedule 13D, and is filing this schedule because of §§ 240.13d-1(e), 240.13d-1(f) or 240.13d-1(g), check the following box.

The information required on the remainder of this cover page shall not be deemed to be "filed" for the purpose of Section 18 of the Securities Exchange Act of 1934 ("Act") or otherwise subject to the liabilities of that section of the Act but shall be subject to all other provisions of the Act (however, see the Notes).

SCHEDULE 13D

CUSIP No. 59318E102

1

Name of reporting person

Bulldog Investors, LLP

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

WC

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 109,810.00
8	Shared Voting Power 3,561,726.00
9	Sole Dispositive Power 109,810.00
10	Shared Dispositive Power 3,561,726.00

11

Aggregate amount beneficially owned by each reporting person

3,671,536.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

14.4 %

14

Type of Reporting Person (See Instructions)

IA

SCHEDULE 13D

CUSIP No. 59318E102

1

Name of reporting person

Phillip Goldstein

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

WC

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 109,810.00
8	Shared Voting Power 3,898,111.00
9	Sole Dispositive Power 109,810.00
10	Shared Dispositive Power 3,898,111.00

11

Aggregate amount beneficially owned by each reporting person

4,007,921.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

15.72 %

14

Type of Reporting Person (See Instructions)

IN

SCHEDULE 13D

CUSIP No. 59318E102

1

Name of reporting person

Andrew Dakos

2

Check the appropriate box if a member of a Group (See Instructions)

(a)
(b)

3

SEC use only

4

Source of funds (See Instructions)

WC

5

Check if disclosure of legal proceedings is required pursuant to Items 2(d) or 2(e)

6

Citizenship or place of organization

UNITED STATES

Number of Shares Beneficially Owned by Each Reporting Person With:

7	Sole Voting Power 0.00
8	Shared Voting Power 3,561,726.00
9	Sole Dispositive Power 0.00
10	Shared Dispositive Power 3,561,726.00

11

Aggregate amount beneficially owned by each reporting person

3,561,726.00

12

Check if the aggregate amount in Row (11) excludes certain shares (See Instructions)

13

Percent of class represented by amount in Row (11)

13.97 %

14

Type of Reporting Person (See Instructions)

IN

SCHEDULE 13D

Item 1.	Security and Issuer
(a)	Title of Class of Securities: Common Stock
(b)	Name of Issuer: MFS High Yield Municipal Trust
(c)	Address of Issuer's Principal Executive Offices: 111 Huntington Avenue, 24TH FLOOR, Boston, MASSACHUSETTS , 02199.
Item 1 Comment: This Constitutes Amendment #9 to the schedule 13D filed July 17, 2023. Except as specifically set forth herein, the schedule 13D remains unmodified.
Item 5.	Interest in Securities of the Issuer
(a)	As per the N-CSRS filed on 7/28/25 there were 25,492,782 shares of common stock outstanding as of 5/31/25. The percentages set forth herein were derived using such number. Phillip Goldstein and Andrew Dakos own Bulldog Investors, LLP, a registered investment advisor. As of December 12, 2025, Bulldog Investors, LLP is deemed to be the beneficial owner of 3,671,536 shares of CMU (representing 14.40% of CMU's outstanding shares) solely by virtue of Bulldog Investors, LLP's power to direct the vote of, and dispose of, these shares. As of December 12, 2025, Mr. Goldstein is deemed to be the beneficial owner of 4,007,921 shares of CMU (representing 15.72% of CMU's outstanding shares) and Mr. Dakos is deemed to be the beneficial owner of 3,561,726 shares of CMU (representing 13.97% of CMU's outstanding shares) by virtue of their power to direct the vote of, and dispose of, these shares.
(b)	Bulldog Investors, LLP has sole power to dispose of and vote 109,810 shares. Bulldog Investors, LLP has shared power to dispose and vote 3,561,726 shares. Certain of Bulldog Investors, LLP's clients (none of whom beneficially own more than 5% of CMU's shares) share this power with Bulldog Investors. Messrs. Goldstein and Dakos are partners of Bulldog Investors, LLP.
(c)	Since the last filing on 11/14/25 the following shares of CMU were purchased. Date Shares Price 12/12/2025 215,000 3.4782 12/11/2025 20,000 3.4797 12/9/2025 20,000 3.4800 12/8/2025 20,000 3.4895 12/5/2025 12,806 3.4900 12/3/2025 14,015 3.4760 12/2/2025 18,500 3.4890 12/1/2025 20,000 3.4899 11/25/2025 20,000 3.5083 11/24/2025 3,735 3.4900
(d)	Clients of Bulldog Investors, LLP and the owners of accounts reflected herein are entitled to receive any dividends or sales proceeds.
(e)	N/A
Item 6.	Contracts, Arrangements, Understandings or Relationships With Respect to Securities of the Issuer
	None
Item 7.	Material to be Filed as Exhibits.
	None

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.

Bulldog Investors, LLP

Signature:	/s/ Andrew Dakos
Name/Title:	Andrew Dakos, Partner
Date:	12/15/2025

Phillip Goldstein

Signature:	/s/ Phillip Goldstein
Name/Title:	Phillip Goldstein
Date:	12/15/2025

Andrew Dakos

Signature:	/s/ Andrew Dakos
Name/Title:	Andrew Dakos
Date:	12/15/2025