Alto Neuroscience, Inc.

Trading Arrangements

During the Company’s last fiscal quarter, certain of our directors and officers (as defined in Rule 16a-1(f) under the Exchange Act)adopted orterminated the contracts, instructions or written plans for the purchase or sale of the Company’s securities set forth in the table below.

On December 17, 2025, Amit Etkin, M.D., Ph.D., our President, Chief Executive Officer, and Chair of the Board, adopted a Rule 10b5-1 trading plan for the potential sale of up to 100,000 shares of our common stock at each of two specified price points (60,000 shares to be sold at $35.00 and 40,000 shares to be sold at $80.00). Transactions under Dr. Etkin’s plan were based upon pre-established dates and stock price thresholds and would only occur upon the expiration of the applicable mandatory cooling-off period. Dr. Etkin’s plan had a termination date of December 31, 2026, or the date all shares subject to the plan had been sold. On March 13, 2026, Dr. Etkin terminated his trading plan, effective March 17, 2026. No sales of common stock occurred under the plan prior to its termination.

On December 23, 2025, Nicholas Smith, our Chief Financial Officer and Chief Business Officer, adopted a Rule 10b5-1 trading plan for the potential sale of up to 14,376 shares of our common stock at a price per share of $45.00. Transactions under Mr. Smith’s plan were based upon pre-established dates and stock price thresholds and would only occur upon the expiration of the applicable mandatory cooling-off period. Mr. Smith’s plan had a termination date of December 31, 2026, or the date all shares subject to the plan had been sold. On March 11, 2026, Mr. Smith terminated his trading plan, effective March 13, 2026. No sales of common stock occurred under the plan prior to its termination.

Both Dr. Etkin’s plan and Mr. Smith’s plan were intended to satisfy the affirmative defense conditions of Rule 10b5-1(c) under the Exchange Act.