Common Stock, par value $0.0001 per share

Monte Rosa Therapeutics, Inc.

321 Harrison Avenue, Boston, MA, 02118

New Enterprise Associates 17, L.P. ("NEA 17"); NEA Partners 17, L.P. ("NEA Partners 17"), which is the sole general partner of NEA 17; and NEA 17 GP, LLC ("NEA 17 LLC" and, together with NEA Partners 17, the "Control Entities"), which is the sole general partner of NEA Partners 17; Anthony A. Florence, Jr. ("Florence"), Mohamad H. Makhzoumi ("Makhzoumi") and Scott D. Sandell ("Sandell"); and Forest Baskett ("Baskett"), Ali Behbahani ("Behbahani"), Carmen Chang ("Chang"), Edward T. Mathers ("Mathers"), Paul Walker ("Walker") and Rick Yang ("Yang"). Florence, Makhzoumi and Sandell are each a member of the Executive Committee of NEA Management Company, LLC (the "Executive Committee"). The persons named in this Item 2 are referred to individually herein as "Reporting Person" and collectively as the "Reporting Persons."

The address of the principal business office of NEA 17, each Control Entity and Sandell is New Enterprise Associates, 1954 Greenspring Drive, Suite 600, Timonium, MD 21093. The address of the principal business office of Makhzoumi is New Enterprise Associates, 2855 Sand Hill Road, Menlo Park, CA 94025. The address of the principal business office of Florence is New Enterprise Associates, 104 5th Avenue, 19th Floor, New York, NY 10011.

The principal business of NEA 17 is to invest in and assist growth-oriented businesses located principally in the United States. The principal business of NEA Partners 17 is to act as the sole general partner of NEA 17. The principal business of NEA 17 LLC is to act as the sole general partner of NEA Partners 17. The principal business of each of the Florence, Makhzoumi and Sandell is to manage the Control Entities, NEA 17 and a number of affiliated partnerships with similar businesses.

During the five years prior to the date hereof, none of the Reporting Persons has been convicted in a criminal proceeding or has been a party to a civil proceeding ending in a judgment, decree or final order enjoining future violations of, or prohibiting or mandating activities subject to, federal or state securities laws or finding any violation with respect to such laws.

NEA 17 LLC is a limited liability company organized under the laws of the State of Delaware. NEA 17 and NEA Partners 17 are limited partnerships organized under the laws of the State of Delaware. Florence, Makhzoumi and Sandell are each a United States citizen.

NEA 17 is the record owner of the NEA 17 Shares. As the general partner of NEA 17, NEA Partners 17 may be deemed to own beneficially the NEA 17 Shares. As the sole general partner of NEA Partners 17, NEA 17 LLC may be deemed to beneficially own the NEA 17 Shares. As individual members of the Executive Committee, which committee has voting and dispositive power with respect to the NEA 17 Shares, each of Florence, Makhzoumi and Sandell may be deemed to beneficially own the NEA 17 Shares. Each Reporting Person disclaims beneficial ownership of the NEA 17 Shares other than those shares which such person owns of record. As of July 6, 2026, Behbahani is the record owner of options to purchase 135,432 shares of Common Stock exercisable within 60 days (the "Behbahani Option Shares"). The percentage of outstanding Common Stock of the Issuer which may be deemed to be beneficially owned by each Reporting Person is set forth on Line 13 of such Reporting Person's cover sheet. Such percentage was calculated based on the 84,479,418 shares of Common Stock reported by the Issuer to be outstanding as of May 1, 2026, as reported on the Issuer's Form 10-Q filed with the Securities and Exchange Commission on May 7, 2026. The percentage set forth on the cover sheet for Behbahani is calculated based on the shares described in the preceding sentence plus the Behbahani Option Shares.

Regarding the number of shares as to which such person has: (i) sole power to vote or to direct the vote: See line 7 of cover sheets (ii) shared power to vote or to direct the vote: See line 8 of cover sheets (iii) sole power to dispose or to direct the disposition: See line 9 of cover sheets (iv) shared power to dispose or to direct the disposition: See line 10 of cover sheets.

On July 1, 2026, NEA 17 made a pro rata distribution of 1,000,000 shares of Common Stock of the Issuer to its general partner and its limited partners for no consideration (the "NEA 17 Distribution"). NEA Partners 17 acquired 15,000 shares of Common Stock of the Issuer as a result of the NEA 17 Distribution and, subsequent to the NEA 17 Distribution, on July 1, 2026, made a distribution of 15,000 shares of Common Stock of the Issuer for no consideration (the "NEA Partners 17 Distribution"), of which 11,830 shares were received by an entity for which Florence, Makhzoumi and Sandell may be deemed to have beneficial ownership. NEA 17 now holds a total of 6,692,298 shares of Common Stock of the Issuer (the "NEA 17 Shares"). On July 2, 2026, the shares indirectly received by Florence, Makhzoumi and Sandell in the NEA Partners 17 Distribution were sold as set forth on Schedule A. No other transactions in the Issuer's Common Stock were effected by the Reporting Persons since the filing of Amendment No. 3.

No other person is known to have the right to receive or the power to direct the receipt of dividends from, or any proceeds from the sale of, Common Stock beneficially owned by any of the Reporting Persons.

As of April 1, 2026, each of Baskett, Behbahani, Chang, Mathers, Walker and Yang has ceased to beneficially own five percent (5%) or more of the Issuer's Common Stock.