Integrase strand transfer inhibitor (INSTI)-containing antiretroviral therapy (ART) is currently the guideline-recommended first-line treatment for HIV. Delayed prescription of INSTI-containing ART may amplify differences and inequities in health outcomes. To estimate racial and ethnic differences in the prescription of INSTI-containing ART among adults newly entering HIV care in the US and to examine variation in these differences over time in relation to changes in treatment guidelines. Retrospective observational study of 42 841 adults entering HIV care from October 12, 2007, when the first INSTI was approved by the US Food and Drug Administration, to April 30, 2019, at more than 200 clinical sites contributing to the North American AIDS Cohort Collaboration on Research and Design. Combined race and ethnicity as reported in patient medical records. Probability of initial prescription of ART within 1 month of care entry and probability of being prescribed INSTI-containing ART. Differences among non-Hispanic Black and Hispanic patients compared with non-Hispanic White patients were estimated by calendar year and time period in relation to changes in national guidelines on the timing of treatment initiation and recommended initial treatment regimens. Of 41 263 patients with information on race and ethnicity, 19 378 (47%) as non-Hispanic Black, 6798 (16%) identified as Hispanic, and 13 539 (33%) as non-Hispanic White; 36 394 patients (85%) were male, and the median age was 42 years (IQR, 30 to 51). From 2007-2015, when guidelines recommended treatment initiation based on CD4+ cell count, the probability of ART initiation within 1 month of care entry was 45% among White patients, 45% among Black patients (difference, 0% [95% CI, -1% to 1%]), and 51% among Hispanic patients (difference, 5% [95% CI, 4% to 7%]). From 2016-2019, when guidelines strongly recommended treating all patients regardless of CD4+ cell count, this probability increased to 66% among White patients, 68% among Black patients (difference, 2% [95% CI, -1% to 5%]), and 71% among Hispanic patients (difference, 5% [95% CI, 1% to 9%]). INSTIs were prescribed to 22% of White patients and only 17% of Black patients (difference, -5% [95% CI, -7% to -4%]) and 17% of Hispanic patients (difference, -5% [95% CI, -7% to -3%]) from 2009-2014, when INSTIs were approved as initial therapy but were not yet guideline recommended. Significant differences persisted for Black patients (difference, -6% [95% CI, -8% to -4%]) but not for Hispanic patients (difference, -1% [95% CI, -4% to 2%]) compared with White patients from 2014-2017, when INSTI-containing ART was a guideline-recommended option for initial therapy; differences by race and ethnicity were not statistically significant from 2017-2019, when INSTI-containing ART was the single recommended initial therapy for most people with HIV. Among adults entering HIV care within a large US research consortium from 2007-2019, the 1-month probability of ART prescription was not significantly different across most races and ethnicities, although Black and Hispanic patients were significantly less likely than White patients to receive INSTI-containing ART in earlier time periods but not after INSTIs became guideline-recommended initial therapy for most people with HIV. Additional research is needed to understand the underlying racial and ethnic differences and whether the differences in prescribing were associated with clinical outcomes.