Recently developed KRAS ^G12C inhibitory drugs are beneficial to lung cancer patients harboring KRAS ^G12C mutations, but drug resistance frequently develops. Because of the immunosuppressive nature of the signaling network controlled by oncogenic KRAS, these drugs can indirectly affect antitumor immunity, providing a rationale for their combination with immune checkpoint blockade. In this study, we have characterized how KRAS ^G12C inhibition reverses immunosuppression driven by oncogenic KRAS in a number of preclinical lung cancer models with varying levels of immunogenicity. Mechanistically, KRAS ^G12C inhibition up-regulates interferon signaling via Myc inhibition, leading to reduced tumor infiltration by immunosuppressive cells, enhanced infiltration and activation of cytotoxic T cells, and increased antigen presentation. However, the combination of KRAS ^G12C inhibitors with immune checkpoint blockade only provides synergistic benefit in the most immunogenic tumor model. KRAS ^G12C inhibition fails to sensitize cold tumors to immunotherapy, with implications for the design of clinical trials combining KRAS ^G12C inhibitors with anti-PD1 drugs.