Monte Rosa Therapeutics : Company Call Presentation - October 17 2023

From Serendipity to Rational Design

Taking Molecular Glue Degraders to New Heights | October 2023

Forward-Looking Statements

These materials include express and implied "forward-looking statements," including forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Forward looking statements include all statements that are not historical facts, and in some cases, can be identified by terms such as "may," "might," "will," "could," "would," "should," "expect," "intend," "plan," "objective," "anticipate," "believe," "estimate," "predict," "potential," "continue," "ongoing," or the negative of these terms, or other comparable terminology intended to identify statements about the future. Forward-looking statements contained in herein include, but are not limited to, statements about our product development activities, including our expectations around the potential of molecular glue degraders ("MGDs"), the potential of our herein detailed pipeline of MGDs, our expectations for our collaboration with Roche, including the discovery and development of MGDs therefrom, and our expectations and estimates of potential future payments available under the collaboration, our ongoing pre-clinical and clinical development of our GSPT1 degrader referred to as MRT-2359, including our expectations regarding the potential relevance of certain interim clinical data, our expectations for the nature and timing of any additional clinical data releases for MRT- 2359, including any full phase 1 clinical data release, and our expectations for the nature and timing of our ongoing and future clinical development of MRT-2359, including our plan to continue the Phase 1/2 study of MRT-2359 and its anticipated timing and progress, and our ability to enroll the requisite number of patients and dose each dosing cohort in the intended manner, the potential for MRT-2359 to benefit patients living with a variety of difficult-to-treat cancers, our expectations regarding the advancement, and timing thereof, of our pipeline and the various products therein, our ability to advance our development candidates, including MRT-6160 and our expectations for MRT-6160 to enter the clinic in 2024 and its potential applications across multiple autoimmune diseases, our expectations regarding potential therapeutic opportunities for our MGDs, and our clinical development expectations therefor, our expectations regarding patient populations and medical needs for any potential therapeutic opportunities for our MGDs, our expectations regarding our proprietary QuEEN™ platform and its potential to be highly productive and an industry-leading platform for designing MGDs to address hard-to-drug disease targets via degradation, combining experimentation with AI to push the boundaries of what is possible with MGDs, and the strength of our financial position, including our estimates of cash runway, among others. By their nature, these statements are subject to numerous risks and uncertainties, as well as those risks and uncertainties set forth in our Annual Report on Form 10-K for the fourth quarter and full year ended December 31, 2022, filed, with the US Securities and Exchange Commission on March 16, 2023, and any subsequent filings, that could cause actual results, performance or achievement to differ materially and adversely from those anticipated or implied in the statements. You should not rely upon forward looking statements as predictions of future events. Although our management believes that the expectations reflected in our statements are reasonable, we cannot guarantee that the future results, performance or events and circumstances described in the forward-looking statements will be achieved or occur. Recipients are cautioned not to place undue reliance on these forward-looking statements, which speak only as of the date such statements are made and should not be construed as statements of fact. We undertake no obligation to publicly update any forward-looking statements, whether as a result of new information, any future presentations or otherwise, except as required by applicable law. Certain information contained in these materials and any statements made orally during any presentation of these materials that relate to the materials or are based on studies, publications, surveys and other data obtained from third-party sources and our own internal estimates and research. While we believe these third-party studies, publications, surveys and other data to be reliable as of the date of these materials, we have not independently verified, and make no representations as to the adequacy, fairness, accuracy or completeness of, any information obtained from third-party sources. In addition, no independent source has evaluated the reasonableness or accuracy of our internal estimates or research and no reliance should be made on any information or statements made in these materials relating to

2 or based on such internal estimates and research. These materials remain the proprietary intellectual property of Monte Rosa Therapeutics and should not be distributed or reproduced in whole or in part without the prior written consent of Monte Rosa Therapeutics.

Monte Rosa Therapeutics - Call Highlights

Interim analysis of data from our Phase I dose escalation study of MRT-2359, providing evidence of optimal PD modulation, clinical activity and a favorable tolerability profile

Partnership with Roche to develop MGDs for oncology and neurological conditions - expands platform reach into neuroscience

Updated cash runway into Q3 2025

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Monte Rosa Therapeutics - Roche Partnership

Monte Rosa Tx - Roche Partnership: Summary

• Discovery partnership on targets in oncology and neurological disease
• Leverages synergies between Monte Rosa Tx - a leading molecular glue degrader company - and Roche - a leading global health care company
• Monte Rosa Tx performs preclinical drug discovery with Roche leading late preclinical discovery and clinical development
• Monte Rosa Tx to receive $50M upfront payment and potential preclinical, clinical, regulatory and sales milestones that could exceed $2B*
• Potential to expand collaboration to additional targets, which triggers potential additional payments including nomination, preclinical, clinical, regulatory and sales milestones
• Partnership provides additional validation of Monte Rosa Tx's QuEEN™ discovery engine and its opportunity to go beyond Oncology
• Monte Rosa Tx's publicly disclosed pipeline remains unencumbered*

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* as disclosed in company 8K