EXAGEN INC.

Rule 10b5-1 trading arrangements

During the three months ended September 30, 2026, none of our directors or officers adopted, modified orterminated a "Rule 10b5-1 trading arrangement" or "non-Rule 10b5-1 trading arrangement," as each term is defined in Item 408 of Regulation S-K.

Amendments to Perceptive Term Loan Facility

On October 19, 2026, the Company and Perceptive Credit Holdings IV, LP (Perceptive) entered into a second amendment (the Second Amendment) to the Credit Agreement and Guaranty, dated April 25, 2025 (Credit Agreement), effective as of September 30, 2026. On November 6, 2026, the Company and Perceptive entered into a third amendment to the Credit Agreement (the Third Amendment). The original Credit Agreement provided for a senior secured delayed draw term loan facility in an aggregate principal amount of up to $75.0 million (the Perceptive Term Loan Facility), which included three additional tranches of funding: up to $10.0 million (the Tranche B Loan), $10.0 million (the Tranche C Loan), and $30.0 million (the Tranche D Loan, and collectively with the Tranche A Loan, the Tranche B Loan and the Tranche C Loan, the Term Loans) to be drawn at the Company's option subject to the Company’s satisfaction of certain conditions, including specified revenue milestones. The Second Amendment and Third Amendment, among other changes, extended the availability of the Tranche B Loan to November 15, 2026, reduced the borrowing amount of the Tranche B Loan from $10.0 million to $5.0 million, and revised certain financial covenant thresholds.

As amended, the Perceptive Term Loan Facility allows the Company to draw up to an aggregate additional principal amount of $35.0 million in two tranches, subject to specified milestone and revenue requirements. The first amendment to the Credit Agreement, Second Amendment, and Third Amendment did not change the stated maturity of the existing Term Loans and reaffirmed the existing liens and guarantees securing the Perceptive Term Loan Facility. The Perceptive Term Loan Facility has a maturity date of April 25, 2030, and all of the Company’s obligations under the Credit Agreement are secured by a first lien perfected security interest on substantially all of its existing and after-acquired assets, subject to customary exceptions.

On November 6, 2026, pursuant to the Third Amendment, the Company and Perceptive also amended the Warrant Certificate to further reduce the aggregate number of shares of common stock subject to future vesting pursuant to the Warrant Certificate by 75,000 shares of common stock that may vest and become exercisable if and when the remaining additional debt tranches are drawn by the Company.

On November 9 2026, the Company satisfied the conditions of the Tranche B Loan and drew down $5.0 million. Following this drawdown, up to $30.0 million of additional principal remains available under the Perceptive Term Loan Facility in a single tranche. In addition, 75,000 shares of common stock vested and became exercisable pursuant to the Warrant Certificate and up to 450,000 shares of common stock remain subject to future vesting.

At-the-Market Offering

On November 9, 2026, the Company, entered the 2026 Sales Agreement with TD Cowen with respect to an at-the-market offering program under which the Company may offer and sell, from time to time at its sole discretion, shares of the 2026 Placement Shares, through TD Cowen as its sales agent.

Under the 2026 Sales Agreement, the Company will set the parameters for the sale of the 2026 Placement Shares, including the number of 2026 Placement Shares to be issued, the time period during which sales are requested to be made, limitations on the number of 2026 Placement Shares that may be sold in any one trading day and any minimum price below which sales may not be made. Subject to the terms of the 2026 Sales Agreement, TD Cowen may sell the 2026 Placement Shares by any method permitted by law deemed to be an “at the market offering” as defined in Rule 415 of the Securities Act, including, without limitation, sales made through the Nasdaq Global Market or on any other trading market for the common stock. TD Cowen will use commercially reasonable efforts to sell the 2026 Placement Shares from time to time, based upon instructions from the Company (including any price, time or size limits or other customary parameters or conditions the Company may impose). The Company will pay TD Cowen a commission equal to three percent (3.0%) of the gross sales proceeds of any 2026 Placement Shares sold through TD Cowen under the 2026 Sales Agreement, and also has provided TD Cowen with customary indemnification and contribution rights.

The Company is not obligated to make any sales of common stock under the Sales Agreement and the Company may not sell any shares of the Company’s common stock in the offering prior to the effectiveness of the 2026 Shelf Registration Statement. The offering of 2026 Placement Shares pursuant to the 2026 Sales Agreement will terminate upon the earlier of (i) the sale of all 2026 Placement Shares subject to the Sales Agreement or (ii) termination of the 2026 Sales Agreement in accordance with its terms.

Any 2026 Placement Shares to be offered and sold under the 2026 Sales Agreement will be issued and sold pursuant to the 2026 Shelf Registration Statement, once the 2026 Shelf Registration Statement is declared effective by the SEC.