Divarasib (GDC-6036), an oral, highly potent and selective next-generation KRAS G12C inhibitor, has demonstrated a manageable safety profile and promising antitumor activity in patients with advanced <i>KRAS G12C</i>-positive non-small cell lung cancer (NSCLC). Here, we report long-term (≥1 year) follow-up of single-agent divarasib from the ongoing, open-label, and multicenter phase I study (ClinicalTrials.gov identifier: NCT04449874). The primary objective was safety, and the other objectives included preliminary antitumor activity. Overall, 65 patients with advanced <i>KRAS G12C</i>-positive NSCLC received single-agent oral divarasib 50-400 mg once daily and 31 patients (48%) were treated beyond 1 year. Divarasib continued to be well tolerated, and the safety profile beyond 1 year was consistent with the overall safety profile. In patients with measurable disease at baseline across all dose levels (n = 63), the confirmed objective response rate was 55.6% (95% CI, 42.5 to 68.1), and the median duration of response was 18.0 months (95% CI, 11.1 to 24.9). The median progression-free survival was 13.8 months (95% CI, 9.8 to 25.4) in the overall population (N = 65) and 15.3 months (95% CI, 12.3 to 26.1) among patients assigned to the 400-mg dose level (n = 44). With extended follow-up, divarasib demonstrated long-term safety and antitumor activity in patients with advanced <i>KRAS G12C</i>-positive NSCLC.