Sound Financial Bancorp, Inc.

(a)None.

(b)During the quarter ended December 31, 2025, Laura Lee Stewart, a director and the Chief Executive Officer of the Company, established a written trading plan (the “Trading Plan”) with an independent trustee in connection with the administration of a charitable remainder trust (the “CRT”). The Trading Plan wasadopted on December 10, 2025 in accordance with Rule 10b5-1(c) under the Securities Exchange Act of 1934 and constitutes a “Rule 10b5-1 trading arrangement” as defined in Item 408(a) of Regulation S-K. The Trading Plan provides pre-established, non-discretionary instructions for the trustee to sell up to 10,800 shares of the Company’s common stock held in the CRT.

Under the Trading Plan, the trustee is authorized to execute sales of Company stock on specified dates and, if needed, pursuant to an objective supplemental formula to fund trust distributions, all without direction or influence from Ms. Stewart. The Trading Plan became effective following the expiration of the mandatory cooling-off period required under Rule 10b5-1(c) and is expected to remain in effect until the earlier of (i) the sale of all shares subject to the Trading Plan, (ii) termination of the CRT, (iii) the Company’s delisting or dissolution, or (iii) Ms. Stewart’s cessation of service as an officer, director or employee of the Company. The arrangement also permits the sale of additional shares that may be contributed to the trust in the future, provided that any such sales are subject to the applicable cooling-off period. All transactions under the Trading Plan will be reported, as applicable, on Forms 4 or 5 pursuant to Section 16 of the Exchange Act.

Ms. Stewart has no ability to modify, suspend, or terminate trades under the Trading Plan, except as permitted under Rule 10b5-1(c).

No other directors or executive officers of the Company adopted orterminated any Rule 10b5-1 trading arrangements or non-Rule 10b5-1 trading arrangements during the quarter ended December 31, 2025.