Rapport Therapeutics, Inc. Fair Value Disclosure

3. Fair Value Measurements

Money market funds are highly liquid and actively traded marketable securities that generally transact at a stable $1.00 net asset value representing its estimated fair value. During the years ended December 31, 2025 and 2024, there were no transfers between Level 1, Level 2 and Level 3.

The Company classifies its marketable securities as short-term because they are available to be converted into cash to fund current operations. The fair value of the Company’s U.S. Treasury bills, government securities, and government agency securities are classified as Level 2 because they are valued using observable inputs to quoted market prices, benchmark yields, reported trades, broker/dealer quotes or alternative pricing sources with reasonable levels of price transparency.

The underlying securities held in the money market funds held by the Company are all government backed securities.

As of December 31, 2025, no investments were in an unrealized loss position. As of December 31, 2024, all investments in an unrealized loss position were in this position for less than 12 months. The Company evaluated its securities for potential

other-than-temporary impairment and considered the decline in market value to be primarily attributable to current economic and market conditions. Additionally, the Company does not intend to sell the securities in an unrealized loss position and does not expect it will be required to sell the securities before recovery of the unamortized cost basis. The Company did not recognize any credit losses during both the years ended December 31, 2025 and 2024.

Valuation of Preferred Stock Tranche Right Liability

The Series B preferred stock tranche right liabilities in the table below are composed of the fair value of obligations to issue Series B convertible preferred stock (see Note 6), either upon achievement of certain specified milestones, upon the waiver of such milestone achievement by a majority vote of the respective series convertible preferred stockholders, or upon a shareholder exercising its right to early exercise the tranche right. The fair value of the tranche right liability was determined based on significant inputs not observable in the market, which represented a Level 3 measurement within the fair value hierarchy. The fair value of the tranche right liabilities were determined using a Contingent Forward Analysis, which is a scenario-based lattice model that accounts for the different possible milestone scenarios and their associated probabilities, as estimated by the Company. The valuation model considered the probability of closing the tranche, the estimated future value of the Convertible Preferred Stock to be issued at each closing and the investment required at each closing. Future values were converted to present value using a discount rate appropriate for probability-adjusted cash flows. The risk-free rate was determined by reference to the U.S. Treasury yield curve for time periods approximately equal to the remaining estimated time to each tranche closing.

Series B Preferred Stock Tranche Right Liability