UNITED STATES SECURITIES AND EXCHANGE COMMISSION WASHINGTON, DC 20549 FORM 10-Q Commission File Number: 001-40522 Monte Rosa Therapeutics, Inc. (Exact name of registrant as specified in its charter) Delaware 84-3766197 (State or other jurisdiction of incorporation or organization) (Mark One) ☒ QUARTERLY REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE ACT OF 1934 For the quarterly period ended March 31, 2026 OR ☐ TRANSITION REPORT PURSUANT TO SECTION 13 OR 15(d) OF THE SECURITIES EXCHANGE A ...

Exhibit 99.1 Monte Rosa Therapeutics Announces First Quarter 2026 Financial Results and Business Updates Presented positive interim Phase 1/2 clinical data of GSPT1-directed MGD MRT-2359 in combination with an AR inhibitor in mCRPC patients with AR mutations; initiation of Phase 2 study evaluating MRT-2359 in combination with apalutamide in mCRPC patients with AR mutations planned for Q3 2026 Interim clinical data from GFORCE-1 trial of NEK7-directed MGD MRT-8102 demonstrated profound CRP reductions in subj ...