Addiction treatment rapidly transitioned to a primarily telehealth modality (telephone and video) during the COVID-19 pandemic, raising concerns about disparities in utilization. To examine whether there were differences in overall and telehealth addiction treatment utilization after telehealth policy changes during the COVID-19 pandemic by age, race, ethnicity, and socioeconomic status. This cohort study examined electronic health record and claims data from Kaiser Permanente Northern California for adults (age ≥18 years) with drug use problems before the COVID-19 pandemic (from March 1, 2019, to December 31, 2019) and during the early phase of the COVID-19 pandemic (March 1, 2020, to December 31, 2020; hereafter referred to as COVID-19 onset). Analyses were conducted between March 2021 and March 2023. The expansion of telehealth services during COVID-19 onset. Generalized estimating equation models were fit to compare addiction treatment utilization during COVID-19 onset with that before the COVID-19 pandemic. Utilization measures included the Healthcare Effectiveness Data and Information Set of treatment initiation and engagement (including inpatient, outpatient, and telehealth encounters or receipt of medication for opioid use disorder [OUD]), 12-week retention (days in treatment), and OUD pharmacotherapy retention. Telehealth treatment initiation and engagement were also examined. Differences in changes in utilization by age group, race, ethnicity, and socioeconomic status (SES) were examined. Among the 19 648 participants in the pre-COVID-19 cohort (58.5% male; mean [SD] age, 41.0 [17.5] years), 1.6% were American Indian or Alaska Native; 7.5%, Asian or Pacific Islander; 14.3%, Black; 20.8%, Latino or Hispanic; 53.4%, White; and 2.5%, unknown race. Among the 16 959 participants in the COVID-19 onset cohort (56.5% male; mean [SD] age, 38.9 [16.3] years), 1.6% were American Indian or Alaska Native; 7.4%, Asian or Pacific Islander; 14.6%, Black; 22.2%, Latino or Hispanic; 51.0%, White; and 3.2%, unknown race. Odds of overall treatment initiation increased from before the COVID-19 pandemic to COVID-19 onset for all age, race, ethnicity, and SES subgroups except for patients aged 50 years or older; patients aged 18 to 34 years had the greatest increases (adjusted odds ratio [aOR], 1.31; 95% CI, 1.22-1.40). Odds of telehealth treatment initiation increased for all patient subgroups without variation by race, ethnicity, or SES, although increases were greater for patients aged 18 to 34 years (aOR, 7.17; 95% CI, 6.24-8.24). Odds of overall treatment engagement increased (aOR, 1.13; 95% CI, 1.03-1.24) without variation by patient subgroups. Retention increased by 1.4 days (95% CI, 0.6-2.2 days), and OUD pharmacotherapy retention did not change (adjusted mean difference, -5.2 days; 95% CI, -12.7 to 2.4 days). In this cohort study of insured adults with drug use problems, there were increases in overall and telehealth addiction treatment utilization after telehealth policies changed during the COVID-19 pandemic. There was no evidence that disparities were exacerbated, and younger adults may have particularly benefited from the transition to telehealth.