NMSIC Co-Investment and Sun Mountain hold 6.04% of Exagen (XGN) shares

Rhea-AI Filing Summary

Exagen Inc. received an updated ownership filing from investment entities NMSIC Co-Investment Fund, L.P. and its general partner, Sun Mountain Capital Partners, L.L.C. The filing reports beneficial ownership of 1,368,958 shares of Exagen common stock, representing 6.04% of the outstanding shares, based on 22,663,099 shares outstanding as of October 31, 2025. The entities state that Sun Mountain, along with its controlling members Brian Birk and Sally Corning, may be deemed to share beneficial ownership of the shares held by NMSIC, while expressly disclaiming beneficial ownership beyond their direct holdings under applicable securities rules.

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SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

SCHEDULE 13G

UNDER THE SECURITIES EXCHANGE ACT OF 1934

(Amendment No. 7)

Exagen Inc.

(Name of Issuer)

Common Stock, par value $0.001 per share

(Title of Class of Securities)

30068X103

(CUSIP Number)

12/31/2025

(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)

SCHEDULE 13G

CUSIP No. 30068X103

1

Names of Reporting Persons

NMSIC Co-Investment Fund, L.P.

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

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 1,368,958.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 1,368,958.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

1,368,958.00

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)

6.04 %

12

Type of Reporting Person (See Instructions)

PN

Comment for Type of Reporting Person: (1) Percentage calculated based on 22,663,099 shares of common stock outstanding as of October 31, 2025, as reported in the issuer's Quarterly Report on Form 10-Q for the quarter ended September 30, 2025.

SCHEDULE 13G

CUSIP No. 30068X103

1

Names of Reporting Persons

Sun Mountain Capital Partners, L.L.C.

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

DELAWARE

Number of Shares Beneficially Owned by Each Reporting Person With:

5	Sole Voting Power 1,368,958.00
6	Shared Voting Power 0.00
7	Sole Dispositive Power 1,368,958.00
8	Shared Dispositive Power 0.00

9

Aggregate Amount Beneficially Owned by Each Reporting Person

1,368,958.00

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)

6.04 %

12

Type of Reporting Person (See Instructions)

PN

Comment for Type of Reporting Person: (1) Percentage calculated based on 22,663,099 shares of common stock outstanding as of October 31, 2025, as reported in the issuer's Quarterly Report on Form 10-Q for the quarter ended September 30, 2025.

SCHEDULE 13G

Item 1.
(a)	Name of issuer: Exagen Inc.
(b)	Address of issuer's principal executive offices: 1261 Liberty Way, Vista, California, 92081
Item 2.
(a)	Name of person filing: This statement is being filed on behalf of each of the following persons (each, a "Reporting Person" and together, the "Reporting Persons"): (i) NMSIC Co-Investment Fund, L.P. ("NMSIC"); and (ii) Sun Mountain Capital Partners, L.L.C. ("Sun Mountain"), the general partner of NMSIC.
(b)	Address or principal business office or, if none, residence: The address of the principal business office of each of the Reporting Persons is: 527 Don Gaspar Avenue Santa Fe, New Mexico 87505
(c)	Citizenship: See row 4 of the cover page of each Reporting Person.
(d)	Title of class of securities: Common Stock, par value $0.001 per share
(e)	CUSIP No.: 30068X103
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: See row 9 of the cover page of each Reporting Person. NMSIC directly owns 1,368,958 shares of common stock, par value $0.001 per share (the "Common Stock"), of the issuer. Sun Mountain is the general partner of NMSIC. The controlling members of Sun Mountain are Brian Birk and Sally Corning. As such, each of these entities and individuals may be deemed to share beneficial ownership of the shares held of record by NMSIC. Pursuant to Rule 13d-4 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), the Reporting Persons declare that filing this Schedule 13G shall not be construed as an admission that any such person is, for the purposes of Section 13(d) and/or Section 13(g) of the Exchange Act, the beneficial owner of any Common Stock covered by this Schedule 13G except to the extent of such person's direct ownership of such Common Stock, and except to the extent of such direct ownership, such beneficial ownership is expressly disclaimed by each such person.
(b)	Percent of class: Each of the Reporting Persons may be deemed to be the beneficial owner of 6.04% of the outstanding shares of the Common Stock. The calculation of beneficial ownership percentage is based on 22,663,099 shares of Common Stock outstanding as of October 31, 2025, as reported by the issuer in its Quarterly Report on Form 10-Q for the quarter ended September 30, 2025, filed with the Securities and Exchange Commission on November 4, 2025.
(c)	Number of shares as to which the person has:
	(i) Sole power to vote or to direct the vote: See row 5 of the cover page of each Reporting Person.
	(ii) Shared power to vote or to direct the vote: See row 6 of the cover page of each Reporting Person.
	(iii) Sole power to dispose or to direct the disposition of: See row 7 of the cover page of each Reporting Person.
	(iv) Shared power to dispose or to direct the disposition of: See row 8 of the cover page of each Reporting Person.
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.
	Not Applicable
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:
	Not Applicable

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.

NMSIC Co-Investment Fund, L.P.

Signature:	/s/ Brian Birk
Name/Title:	Brian Birk, Managing Member of Sun Mountain Capital Partners, L.L.C., the general partner of NMSIC Co-Investment Fund, L.P.
Date:	02/11/2026

Signature:	/s/ Sally Corning
Name/Title:	Sally Corning, Managing Member of Sun Mountain Capital Partners, L.L.C., the general partner of NMSIC Co-Investment Fund, L.P.
Date:	02/11/2026

Sun Mountain Capital Partners, L.L.C.

Signature:	/s/ Brian Birk
Name/Title:	Brian Birk, Managing Member
Date:	02/11/2026

Signature:	/s/ Sally Corning
Name/Title:	Sally Corning, Managing Member
Date:	02/11/2026

FAQ

How many Exagen (XGN) shares do NMSIC and Sun Mountain report owning?

They report beneficial ownership of 1,368,958 shares of Exagen common stock. This stake is held directly by NMSIC Co-Investment Fund, L.P., with Sun Mountain Capital Partners, L.L.C. as its general partner sharing deemed beneficial ownership under securities rules.

What percentage of Exagen (XGN) does NMSIC’s stake represent?

The filing states the position represents 6.04% of Exagen’s outstanding common stock. This percentage is calculated using 22,663,099 shares outstanding as of October 31, 2025, as reported in Exagen’s Quarterly Report on Form 10-Q.

Who are the reporting persons in this Exagen (XGN) Schedule 13G/A?

The reporting persons are NMSIC Co-Investment Fund, L.P. and Sun Mountain Capital Partners, L.L.C.. Sun Mountain is the general partner of NMSIC and its controlling members are identified as Brian Birk and Sally Corning in the ownership disclosure.

What is the basis for the 6.04% ownership calculation in Exagen (XGN)?

The 6.04% ownership figure is based on 22,663,099 shares of Exagen common stock outstanding as of October 31, 2025. That share count comes from Exagen’s Form 10-Q for the quarter ended September 30, 2025, referenced in the ownership statement.

Do the reporting persons fully admit beneficial ownership of all Exagen (XGN) shares reported?

They state that each entity and individual may be deemed to share beneficial ownership of the shares held by NMSIC. However, relying on Rule 13d-4, they expressly disclaim beneficial ownership beyond each person’s direct ownership of Exagen common stock.

Where are the Exagen (XGN) reporting persons based?

Both reporting persons list their principal business office at 527 Don Gaspar Avenue, Santa Fe, New Mexico 87505. Exagen Inc.’s principal executive offices are separately listed as 1261 Liberty Way, Vista, California 92081 in the ownership disclosure.