SCHEDULE 13G/A 0001140361-20-020885 0001788331 XXXXXXXX LIVE 6 Common Stock, par value $0.001 per share 03/25/2025 0001274737 EXAGEN INC. 30068X103 1261 Liberty Way Vista CA 92081 Rule 13d-1(d) NMSIC Co-Investment Fund, L.P. DE 1758958 0 1758958 0 1758958 N 9.83 PN (1) Percentage calculated based on 17,898,098 shares of common stock outstanding as of March 7, 2025, as reported in the issuer's Annual Report on Form 10-K for the year ended December 31, 2024. Sun Mountain Capital Partners, L.L.C. DE 1758958 0 1758958 0 1758958 N 9.83 PN (1) Percentage calculated based on 17,898,098 shares of common stock outstanding as of March 7, 2025, as reported in the issuer's Annual Report on Form 10-K for the year ended December 31, 2024. EXAGEN INC. 1261 Liberty Way, Vista, California, 92081 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. The address of the principal business office of each of the Reporting Persons is: 527 Don Gaspar Avenue Santa Fe, New Mexico 87505 See row 4 of the cover page of each Reporting Person. Y See row 9 of the cover page of each Reporting Person. NMSIC directly owns 1,758,958 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, Sally Coming and Lee Rand. 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. Each of the Reporting Persons may be deemed to be the beneficial owner of 9.83% of the outstanding shares of the Common Stock. The calculation of beneficial ownership percentage is based on 17,898,098 shares of Common Stock outstanding as of March 7, 2025, as reported by the issuer in its Annual Report on Form 10-K for the year ended December 31, 2024, filed with the Securities and Exchange Commission on March 11, 2025. See row 5 of the cover page of each Reporting Person. See row 6 of the cover page of each Reporting Person. See row 7 of the cover page of each Reporting Person. See row 8 of the cover page of each Reporting Person. Y Y Y Y Y Y NMSIC Co-Investment Fund, L.P. /s/ Brian Birk 04/17/2025 /s/ Lee Rand 04/17/2025 Sun Mountain Capital Partners, L.L.C. /s/ Brian Birk 04/17/2025 /s/ Lee Rand 04/17/2025