1 42nd Annual J.P. Morgan Healthcare Conference Developing and Delivering Next Generation Therapies that Improve the Lives of People Living with Cancer Wednesday January 10, 1:30 PM PT

2 This presentation contains forward-looking statements within the meaning of the Private Securities Litigation Reform Act of 1995. Words such as "may," "will," "expect," "plan," "anticipate," "estimate," "intend,“ “could,” “believe,” “goal,” “projections,” “indicate,” “potential,” “opportunity,” and similar expressions (as well as other words or expressions referencing future events, conditions or circumstances) are intended to identify forward- looking statements. Forward-looking statements in this presentation include, but are not limited to, those relating to expectations for the commercial success of COSELA® (trilaciclib), our ability to further develop and expand the use of COSELA in the treatment of extensive-stage small cell lung cancer, the therapeutic potential of trilaciclib in the treatment triple-negative breast cancer and with ADCs, that trilaciclib’s greatest effect is on longer term endpoints including OS, that trilaciclib may improve long-term immune surveillance for additional benefit after treatment, the expectation that achievement of the OS endpoint in the ongoing PRESERVE 2 Phase 3 clinical trial is expected to enable global regulatory submissions in 2024 and beyond, that G1’s cash runway is expected to extend into 2025, that impact from platinum based chemotherapy shortages have begun to abate, global expansion, and that achieving the OS primary endpoint in the Phase 3 TNBC trial may serve as a catalyst for global expansion plans. In addition, COSELA may not achieve the degree of market acceptance for commercial success, the potential to demonstrate trilaciclib + gem/carbo as 1L TNBC standard of care, and the impact of pandemics such as COVID-19 (coronavirus), are based on our expectations and assumptions as of the date of this presentation. Each of these forward-looking statements involves risks and uncertainties that may cause our actual results to materially differ from those expressed or implied in such statements. Investors, potential investors, and others should give careful consideration to these risks and uncertainties. Applicable risks and uncertainties are discussed in our filings with the U.S. Securities and Exchange Commission, including the "Risk Factors" sections contained therein and include, but are not limited to, our ability to successfully commercialize COSELA; the dependence on the commercial success of COSELA; our ability to complete clinical trials for, obtain approvals for, and commercialize additional indications of COSELA and any of our product candidates other than COSELA; our initial success in clinical trials may not be indicative of results obtained when these trials are completed or in later stage trials; the inherent uncertainties associated with developing new products or technologies and operating as a commercial-stage company; chemotherapy shortages and market conditions. Except as required by law, we assume no obligation to update any forward-looking statements contained herein to reflect any change in expectations, even as new information becomes available. Forward-Looking Statements G1Therapeutics® and G1Therapeutics logo and COSELA® and COSELA logo are trademarks of G1 Therapeutics, Inc. ©2024 G1 Therapeutics, Inc.

3 G1 Therapeutics: Opportunities for Significant Growth • Novel product that provides meaningful patient benefits via transient G1 arrest of HSPC’s and T-Cells • Established U.S. commercial infrastructure with growing revenue in initial ES-SCLC indication • Phase 3 readout provides important potential near-term global commercial opportunity (interim analysis in 1Q) • Robust OS observed in randomized Phase 2 with improvement continuing with subsequent therapies • Phase 2 with sacituzumab govitecan serves as proof-of-concept for trilaciclib in TROP2 ADC combinations • Observing robust safety and tolerability improvements with potential survival benefit • Evaluating additional late-stage studies and conducting research into next generation products • Planning to secure a partner for global expansion following a successful 1L TNBC readout • Anticipated cash runway into 2025 Unique Marketed Product in U.S. with Growing Revenue Potential to Transform 1L TNBC Treatment Opportunity to Improve Safety and Efficacy of Leading ADCs Positioned for Global Expansion and Future Growth Note: HSPC’s: Hematopoietic stem and progenitor cells, ES-SCLC: Extensive Stage Small Cell Lung Cancer, TNBC: Triple negative breast cancer; ADC” antibody-drug conjugate

4 Agenda Unique Marketed Product in U.S. with Growing Revenue Potential to Transform 1L TNBC Treatment Opportunity to Improve Safety and Efficacy of Leading ADCs Positioned for Global Expansion and Future Growth

5 Trilaciclib Mechanism of Action Temporarily Blocks Progression through Cell Cycle Via Transient CDK4/6 Inhibition Key Benefits M G2 S G1 Myeloid Lineages Lymphoid Lineages HSPCs Protects Bone Marrow and Immune System from Cytotoxic Damage During Treatment Improves Long-Term Immune Surveillance for Additional Benefit After Treatment Transiently arrests HSPCs and T cells in G1 Phase Potential Benefits

6 Potent and selective CDK4 and CDK6 inhibition Unique Product Attributes for Robust Transient G1 Arrest IV administration Short half-life Critical Characteristics of Trilaciclib Enabling Robust Transient G1 Arrest These attributes are critical to maximize the benefits of transient CDK4/6 inhibition Precisely timed effect through rapid IV onset Robust G1 arrest through targeted activity Optimizes ability for T-cells to proliferate

7 1. Based on ~20k patients and $36,600 current WAC pricing for 24 vials of trilaciclib (assumed 4 cycles per patient based on standard 1L ES-SCLC chemotherapy regimens) 2. According to active prescriber data from internal ATU Tracking Studies, Q3 2023, which is further supported by Real World Evidence 3. Prescriber data from internal ATU Tracking Studies, Q3 2023 Meaningful opportunity to continue growing share in $700M+ U.S. ES-SCLC market, with high levels of satisfaction expressed by existing prescribers ~20K ES-SCLC Patients in U.S. Receive Indicated Chemotherapy $700M+ Market Opportunity1 Satisfaction with COSELA® (trilaciclib)3 91% 86% 5% 14% 4% 0% 25% 50% 75% 100% % of Oncologists % of NP/PAs Very Satisfied / Satisfied Neutral Very Dissatisfied / Dissatisfied ~10% Current Market Penetration High satisfaction among active prescribers driven by fewer hospitalizations and protection of multiple cell lineages2 Potential for Strong Growth within U.S. ES-SCLC Market