Alector, Inc. Debt Disclosure

10. Debt

On November 14, 2024 (the Closing Date), the Company entered into a loan and security agreement (the Loan Agreement) with its subsidiary Alector LLC as a co-borrower, several banks and other financial institutions from time to time party thereto (collectively, the Lenders) and Hercules Capital, Inc., as administrative agent and collateral agent. The Loan Agreement provides for a senior secured term loan facility in an aggregate principal amount of up to $50.0 million, available in up to two tranches (the Term Loans). The initial tranche of Term Loans in an aggregate principal amount of up to $25.0 million is available through June 30, 2026, subject to the satisfaction of applicable conditions set forth in the Loan Agreement. The second tranche of Term Loans in an aggregate principal amount of up to $25.0 million is available at the sole discretion of the Lenders.

Borrowings under the Loan Agreement accrue interest at a rate equal to the greater of (A) the prime rate plus 1.05% and (B) 8.05%. The Term Loans are repayable in monthly interest-only payments until December 1, 2026 (the Interest-Only Payment Period). The Interest-Only Payment Period may be extended by up to twenty-four (24) months, subject to the achievement by the Company of certain milestones as set forth in the Loan Agreement. After the expiration of the Interest-Only Payment Period, the Term Loans are repayable in equal monthly payments of principal and accrued interest until maturity. The Term Loans will mature on December 1, 2028 (the Maturity Date). At the Company’s option, the Company may prepay all or a portion of the outstanding Term Loans, subject to a prepayment premium equal to (a) 1.5% of the Term Loans being prepaid if the prepayment occurs after the 12 month anniversary of the Closing Date but on or prior to the 24 month anniversary of the Closing Date; and (b) 0.5% of the Term Loans being prepaid if the prepayment occurs after 24 months following the Closing Date and prior to the Maturity Date. In addition, the Company will pay an end of term charge of (i) 2.45% if the Term Loans are prepaid or repaid within the first 24 months of the Closing Date; or (ii) 4.75% if the Term Loans are prepaid or repaid after 24 months from the Closing Date (including on the Maturity Date). The Company paid an initial facility charge of $250,000 on the Closing Date, and thereafter, the Company will pay a facility charge of 1.00% upon any draw of the Term Loans under the second tranche. The Company’s obligations under the Loan Agreement are secured by substantially all of the Company’s assets, including intellectual property, subject to certain exceptions, including

exceptions with respect to assets and intellectual property subject to the Company’s existing agreements with each of Adimab LLC and Glaxo Wellcome UK Limited, and previously subject to the agreement with AbbVie Biotechnology, Ltd.

The Loan Agreement contains customary affirmative and negative covenants, including covenants limiting the ability of the Company and their subsidiaries to, among other things, dispose of assets, enter into certain licensing arrangements, effect certain mergers, incur debt, grant liens, pay dividends and distributions on their capital stock, make investments and acquisitions, and enter into transactions with affiliates, in each case subject to customary exceptions for a loan facility of this size and type. The Loan Agreement also includes customary events of default, including, among others, payment defaults, material misrepresentations, breaches of covenants following any applicable cure period, cross defaults with certain other indebtedness or material agreements, bankruptcy and insolvency events, judgment defaults and the occurrence of certain events that could reasonably be expected to have a “material adverse effect.” The occurrence of an event of default could result in the acceleration of the Company’s obligations under the Loan Agreement, the termination of the Lenders’ commitments, a 5% increase in the applicable rate of interest and the exercise by Agent of other rights and remedies provided for under the Loan Agreement.

On November 14, 2024, the Company drew down $10 million from the initial tranche and received proceeds of approximately $9.6 million after charges payable to Hercules Capital. The Company incurred $0.4 million in debt issuance costs in relation to the initial draw. As of December 31, 2025, the face value of the outstanding balance of the Term Loan was $10 million, less unamortized discount and unaccreted value of the End of Term Charge of $0.3 million based on the imputed interest rate of 11.5%. The fair value of the Term Loan as of December 31, 2025 is a Level 3 measurement considered to approximate its carrying value of $9.7 million. In 2025, the applicable interest rate averaged approximately 8.4%. The Term Loan bears interest at a variable rate based on the Prime Rate, subject to an interest rate floor, which limited the impact of changes in benchmark interest rates on the fair value of the Term Loan. In addition, the Term Loan has a remaining maturity of approximately three years, and there have been no significant changes in the Company’s credit risk since inception.