X0609 4 2026-09-01 0 0001274737 EXAGEN INC. XGN 0001449439 Black Jeffrey G. false C/O EXAGEN INC. 1261 LIBERTY WAY VISTA CA 92081 0 1 0 0 Chief Financial Officer 0 Common Stock 2026-09-01 4 S 0 20614 7.2175 D 323339 D Common Stock 2026-09-01 4 A 0 1571 3.0175 A 324910 D The sale reported on this Form 4 represents shares sold by the Reporting Person, at the direction of the Issuer, to cover tax withholding obligations in connection with the vesting and settlement of Restricted Stock Units. The sale is mandated solely by the Issuer and does not represent a discretionary transaction by the Reporting Person. The reporting person is voluntarily reporting the acquisition of the common stock pursuant to the Issuer's Employee Stock Purchase Plan ("ESPP"). Represents shares of common stock purchased through the ESPP in transactions that were exempt under both Rule 16b-3(d) and Rule 16b-3(c). /s/ Jeffrey G. Black 2026-09-02